MANAGING GLYPHOSATE RESISTANCE

Transcription

1 MANAGING GLYPHOSATE RESISTANCE Tony Cook Abul Hashem Jenna Malone Chris Preston Andrew Storrie David Thornby Steve Walker Michael Walsh Jeff Werth Catherine Borger March 2013 In partnership with funded by 1

2 1. Introduction 4 2. Executive summary 5 3. Evolution and identification of glyphosate resistance 9 4. Strategies to delay and avoid glyphosate resistance Residual herbicides and knockdowns Summer cropping Timeliness of treatment Managing single or multiple flushes Controlling survivors of glyphosate applications Risks of cross and multiple resistance Monitoring and testing for glyphosate resistance Test timing Methods Sample collection Results Seed Testing and Quick-Test service Management of glyphosate resistance Summer grasses Strategic Integrated Weed Management (IWM) Control in Fallow Herbicide options Non-herbicide options Fleabane Problem overview Identification Time of emergence Fleabane seeds Strategic management approach Control tactics Annual Ryegrass Crop and fallow situations Strategic approach Effective treatments in fallow Effective treatment in crop Roundup Ready canola Fence lines Vineyards 45 2

3 7.4 Seed destruction Weed seed production and selection of resistant weeds Targeting weed seed production after crop flowering Targeting annual weed seed at harvest Quarantine Contamination Point 1: Crop seed Contamination Point 2: Farm machinery and vehicles Contamination Point 3: Livestock feeding and movement Contamination Point 4: Non-crop areas Other contamination points Case Study Management of glyphosate resistant annual ryegrass in a mixed farm in Western Australia Introduction Property characteristics Management program Conclusions Case Study Management of glyphosate resistant awnless barnyard grass and annual ryegrass in northern NSW Introduction Property characteristics Management program Conclusions Case Study Management of glyphosate resistant liverseed grass in northern NSW Introduction Property characteristics Management program Further Information Local contacts Useful websites 73 3

4 1. Introduction Glyphosate is the most widely-used herbicide in agricultural production in Australia. It also finds wide use outside agriculture. Resistance evolution currently threatens the sustainability of glyphosate and unfortunately, for many of the uses, there is no replacement for glyphosate that is as cost-effective, as easy to use and as environmentally benign. Therefore, management change is crucial to sustaining the utility of this herbicide. Glyphosate resistance was first reported in Australia in 1996 and since then ongoing research on managing and preventing glyphosate resistance has been undertaken. The recognition that much of the information about glyphosate resistance and its management is dispersed in research reports, fact sheets and research publications has brought about the development of this publication. It is an attempt to collate the crucial information about glyphosate resistance and the best bet management for Australian farming systems into one document including a series of case studies of glyphosate resistance management. The aim of this report is to be a valuable resource for growers and advisors in the management of glyphosate resistant weeds. Much of the research described in this guide was funded by the Grains Research and Development Corporation (GRDC) through grants to several of the authors. The authors wish to thank GRDC and acknowledge the GRDC s support. 4

5 2. Executive summary The introduction and use of glyphosate in western farming systems has helped transform the way crops are grown and weeds are controlled. It has enabled crops to be grown with minimal cultivation, reduced the risk of erosion and allowed the efficient storage of water in the soil, giving more reliable crop yields. While glyphosate has been seen as a wonder herbicide this success has lead to the over-reliance on this one herbicide and the evolution of weed populations that are no longer controlled by glyphosate. Over-reliance has also caused the increase in glyphosate-tolerant weeds, that is, those species that were never controlled by glyphosate. The increase in use of Roundup Ready crops and glyphosate for crop-topping will increase the selection pressure for resistance to this herbicide. Around the world there are currently 24 species in total with populations which can no longer be controlled using glyphosate. Eleven species are broadleaf weeds and 13 are grass weeds. At present, Australia has six species with populations resistant to glyphosate. Annual ryegrass (Lolium rigidum) was the world s first case of resistance to glyphosate and was found in northern Victoria in This gave Australia a head start in the research and management of glyphosate resistance. The delay or the prevention of the evolution of resistance-dominated populations requires the use of other weed control tactics which effectively control both glyphosate resistant and susceptible plants. The evolution of glyphosate resistance can be slowed, and in some cases prevented, by using combinations of non-glyphosate herbicides, and non-herbicide tactics including tillage and crop competition. Residual herbicides have some advantages for inclusion in a preventative strategy. In particular, they can offer some level of control on more than one flush of weeds, if the time of application and emergences coincide. However, the efficacy of a residual herbicide on any one cohort is often only average. This indicates that residual herbicides are unsuitable as the only nonglyphosate control if the aim is to slow or prevent resistance. Knockdown alternatives to glyphosate are less able to provide control over multiple cohorts. However, they can be timed to provide higher levels of control than residual herbicides. Early intervention is more successful at delaying glyphosate resistance than waiting for resistance levels to increase in the population before introducing new tactics. Strategies that attack all flushes in a year and include alternative herbicides or tillage are more successful at slowing or preventing glyphosate resistance than strategies that allow cohorts to be controlled with glyphosate only. Deliberately controlling survivors of glyphosate applications can be done through separate applications of non-glyphosate tactics, or with an appropriately used double knock. Cross resistance and multiple resistance including glyphosate is possible. In Australia to date multiple selection events have lead to annual ryegrass populations with both glyphosate and paraquat resistance and another population with both glyphosate and Group A resistance. Where non-herbicide tactics are not practical or not effective, care should be taken with the choice of alternative herbicides. Understanding the resistance risks of alternative herbicide groups is crucial. 5

6 Identifying resistance Glyphosate resistance appears initially in a few isolated plants. These are often healthy or obviously re-growing and surrounded by dead plants of the same weed species. In the following seasons, patches of survivors can develop from these isolated plants if they are not prevented from setting seed. Growers should consider testing for glyphosate resistance if: their paddocks are at risk for resistance, and/or plants survive the glyphosate application. The two commercial tests for glyphosate resistance use either seeds and and/or whole plants. Seed or whole plants need to be sampled from a representative area of surviving plants. It is important to record the location of these collection sites on a mud map or with a GPS. Appropriate preventive actions should be implemented by reducing the reliance on glyphosate and taking actions to stop seed-set on survivors of glyphosate spraying regardless of test result. Management of glyphosate resistance Summer grasses - are among the weed species with the highest potential to develop resistance to glyphosate. In Queensland and New South Wales there are now many populations of awnless barnyard grass and some populations of windmill and liverseed grass resistant to glyphosate. The high susceptibility of summer grasses to glyphosate resistance is caused by: Reliance on glyphosate for the majority of grass control; Limited options for fallow control other than glyphosate; Limited post-emergent options for control in crop; High seed production of summer grasses; Grasses that are usually present in high densities; Limited use of cultivation as a weed control tactic; and Treatment of plants under hot dry conditions killing the susceptible proportion of the population while mildly tolerant individuals to survive. Flaxleaf fleabane (Conyza bonariensis) is a major weed burden in no-till cropping in southern Queensland and northern New South Wales. It is also emerging as a major problem across cropping regions of southern Australia. Glyphosate resistant populations have been collected from summer fallow and roadsides. Farmers are now reliant on strategic cultivation and double knocking large plants to obtain high levels of kill. Use of late post-emergent herbicides in cereal crops is becoming an important management technique in spring. Glyphosate resistant annual ryegrass requires a well planned approach including herbicide resistance testing to determine which herbicides are effective. This is recommended for every affected paddock as there may be significant differences in resistance levels between paddock samples. Additionally, ryegrass might also be resistant to more than one herbicide mode-of-action (MOA). 6

7 Strategic Integrated Weed Management (IWM) Regardless of the weed species to be managed the following points are critical to the successful management of glyphosate (and all other modes-of-action) resistance: Know what the history of herbicide use is in each paddock. If glyphosate has been predominately used, it s time to change; Know what herbicides are effective on key weeds and aim for optimum control e.g. herbicide resistance testing; Rotate between herbicide groups; Use a selection of non-herbicide control options whenever the opportunity arises; Always monitor each control tactic thoroughly; Ensure survivors do not set seed to replenish the soil seed bank; Avoid the introduction or spread of weeds by contaminated seed, grain, hay, stock or machinery; Manage weeds in surrounding non-crop areas (e.g. fences, tracks, silos and sheds); and Review the completed control regime and adjust future management strategies accordingly. Case Study Management of glyphosate resistant annual ryegrass in the wheatbelt of Western Australia On a mixed enterprise farm near Northam, Western Australia, glyphosate resistant annual ryegrass developed in a vineyard in 2004 caused by the repeated application of glyphosate. By 2007, glyphosate resistant ryegrass was spreading from the vineyard to the surrounding ryegrass-based pasture fields. The ryegrass was also infected with annual ryegrass toxicity (ARGT). The farmer wished to maintain annual ryegrass on the property as a forage species and to reduce the use of herbicides. Therefore the grower aimed to maintain a high population of annual ryegrass in the fields around the vineyard. Sowing Safeguard ryegrass and spreading the twist fungus were successful in managing ARGT and no stock died. Sowing Safeguard ryegrass also increased the density of glyphosatesusceptible plants on the farm and their pollen production was maximised by lenient grazing at flowering. Only six glyphosate resistant ryegrass plants were found on the property in late This reduction since 2008 is due to a minor weakness glyphosate resistant ryegrass carries, allowing susceptible plants to compete if glyphosate is not used. Management of glyphosate resistant awnless barnyard grass and annual ryegrass in northern NSW There are two species of weeds resistant to glyphosate on this farm at Bellata in northern NSW. The first and most widespread species is awnless barnyard grass and resistance was first suspected in the summer of 2004/05 and later confirmed in 2007/08. The second species exhibiting resistance to glyphosate is annual ryegrass and was suspected of being resistant in 2010 and confirmed in The extent of the annual ryegrass infestation is limited to a patch less than a hectare. 7

8 Integrated strategies used to successfully manage glyphosate resistant awnless barnyard grass included: Removing sorghum and sunflower from the rotation in affected paddocks as these crops increase barnyard grass densities. Most of the control tactics are employed in the fallow phase. Using Flame (Group B) and atrazine (Group C) as a pre-emergent fallow treatment applied in early spring. This tank mix was the superior pre-emergence treatment confirmed in research trials and farmer demonstrations. Regularly monitoring affected paddocks and hand weeding light infestations of barnyard grass. This occurred after barnyard grass populations were reduced to extremely low levels. Cultivating large barnyard grass of sizes greater than mid tillering stage. There are no registered chemical options to control barnyard grass beyond the early tillering stage, except glyphosate. Applying the double knock technique in fallow: Either using a Group A herbicide or Flame (Group B) followed with a Group L herbicide. After four years of active management, the density of barnyard grass is approximately 10 plants per ha. Although the farmer now uses a hand weeding strategy to control survivors, reliance on effective pre-emergence herbicides remains a critical part to glyphosate resistant barnyard grass management. Management of glyphosate resistant liverseed grass in northern NSW A Pallamallawa farmer and his agronomist noticed a suspect patch of liverseed grass in the summer of 2007/08. Plants were immediately sent for resistance testing using the Quick-test and resistance to glyphosate was confirmed. Since then the farmer has been unrelenting in his efforts to control the small patch (<1 ha) of liverseed grass. Successful methods used for the control for liverseed grass were: Flame (Group B) as a fallow pre-emergence treatment early in the summer fallow; Double knock - maximum label rates of glyphosate followed by a bipyridyl (Group L) herbicide; Double cultivation with wide sweep points to ensure full disturbance, followed by monitoring to ensure 100% kill; and Brown manuring of winter cereals using the decaying biomass as a mulch to reduce liverseed grass establishment. This case study highlights the importance of early detection, herbicide resistance testing and focused weed management and monitoring. The implementation of effective management was easy as the farmer had the confidence to change. 8

9 3. Evolution and identification of glyphosate resistance Glyphosate resistance has evolved in six (6) weed species in Australia to date: annual ryegrass, barnyard grass, liverseed grass, fleabane, windmill grass and great brome. The table below provides an overview of the situations where glyphosate resistance has evolved. Table 1: Situations where glyphosate resistant weeds have evolved Situation Number of sites States Broadacre cropping Chemical fallow Winter grains pre sowing Summer grains Irrigated crops NSW, Qld, WA NSW, Vic, SA, WA NSW SA Horticulture Tree crops Vine crops Vegetables NSW, SA SA, WA Vic Other Driveway Around buildings Fence line/crop margin Irrigation channel Airstrip Railway Roadside NSW, SA, Vic, WA NSW NSW, SA, Vic, WA NSW, SA, Vic SA WA, NSW SA, NSW, Qld, WA For latest survey results refer to 9 Many of the situations where glyphosate resistance has evolved are characterised by intensive use of glyphosate over many years, no crop competition and no or few other effective weed control tactics used. Such situations include: chemical fallows, orchards, vineyards, irrigation channels, fence lines and other un-cropped areas of the farm. Herbicide resistance typically evolves following the survival of a small number of resistant individuals within the population. The vast majority of susceptible weeds are killed when herbicides are used. Within the resistant individuals there will be a small number which will pass the resistance trait onto their progeny, causing the frequency of resistant genes to increase within the population. Over time, the number of resistant individuals within the population will increase until the population can no longer be controlled by that particular herbicide. Glyphosate resistance is occurring in areas with no competition from crops or other vegetation for the following reasons: High frequencies of glyphosate application as the only weed control tactic; and Lack of competition from other plants allowing resistant weeds to set a lot of seed, rapidly increasing the resistant seed bank. As areas such as fence lines, firebreaks, irrigation channels and around buildings are kept free of vegetation, glyphosate resistance is easily noticed. However, glyphosate resistance can occur in crops and its presence is more likely to remain unnoticed for an extended period of time, as the resistance will increase more slowly and may be hidden. Newer uses of glyphosate, such as in Roundup Ready crops and for crop-topping, can trigger glyphosate resistance. Roundup Ready crops allow glyphosate to be used later in the crop season, increasing the proportion of the weed population treated with glyphosate as later germinations will also be sprayed. Plants that are resistant to glyphosate as seedlings are also resistant to glyphosate

10 when setting seed. Therefore crop-topping with glyphosate will not be effective in controlling glyphosate resistant plants. Figure 1: Patch of glyphosate resistant weeds not controlled by glyphosate (C. Preston). When glyphosate resistance first occurs it will typically appear as small patches of resistant individuals surviving treatment, while surrounding individuals are controlled. It is also possible there will be individual resistant plants scattered some distance from the original patch. If not controlled, these plants will become foci for new patches of resistant plants. This should not be mistaken for the effect glyphosate can still have on resistant individuals, causing signs of damage such as wilting, yellowing and cessation of growth. However, the plants will grow out of the damage within a few weeks. Glyphosate resistance can be confused with the lack of control due to other factors. Glyphosate has little soil activity, so weeds emerging after herbicide application will not be controlled. These weeds may or may not be resistant to glyphosate. Poor spraying conditions (e.g. too hot and dry, too dusty), stressed weeds and poor water quality can reduce the effectiveness of glyphosate. A good way to determine whether survival is caused by resistance, is to observe weeds controlled by glyphosate occurring adjacent to weeds that are alive and growing healthily. In order to be certain that resistance is the cause of a glyphosate failure, a resistance test should be undertaken. Identifying glyphosate resistance early before it has had the opportunity to spread across the farm is important for effective management. 10

11 Figure 2: Surviving annual ryegrass among plants controlled by glyphosate (C. Preston). It also has to be noted that machinery and water flow can spread resistant weed seed from the original source and, over time, a large area can become infested. For some species, such as fleabane and windmill grass, wind also disperses weed seeds, allowing the resistant weeds to spread widely. Crop-Topping Is the use of a knockdown herbicide over the crop which has just matured while the weeds, such as annual ryegrass, are still forming seeds. This technique can reduce ryegrass seed set by between 50 and 90%. 11

12 4. Strategies to delay and avoid glyphosate resistance The evolution of glyphosate resistance in a weed population is directly connected to the continued use of glyphosate. The more often glyphosate is used, the faster the population will change from mostly susceptible to mostly resistant as mainly resistant individuals can set viable seeds. The delay or the prevention of the evolution of resistance-dominated populations requires the use of other weed control tactics which effectively control both glyphosate resistant and susceptible plants. The more non-glyphosate control tactics are used, the more the development of glyphosate resistance can be prevented or delayed. Glyphosate resistance takes over a decade to evolve, so computer modelling is a useful way to predict suitable tactics to delay the onset of resistance. The Queensland Department of Agriculture, Fisheries and Forestry have developed a glyphosate resistance model that allows the investigation of different scenarios to delay or avoid resistance. The use of glyphosate intensively in fallows has been identified as the worst-case scenario for glyphosate resistance in grain cropping. For barnyard grass, this means zero-till continuous winter cropping and glyphosate used to control weeds in summer fallows. Any system that uses something other than glyphosate in summer is an improvement on glyphosate alone. However, results from the model show that infrequent or poorly-targeted controls provide little or no real benefit. The evolution of glyphosate resistance can be slowed, and in some cases prevented, by using combinations of non-glyphosate herbicides, tillage and crop competition. The number of times a non-glyphosate option is included in a rotation determines how successful any given strategy is likely to be. The glyphosate resistant model predicts that the following factors will provide the best chance of success: 1. Use a combination of residual and knockdown tactics: residual herbicides alone are not sufficient. 1. Use a combination of crops and fallows to provide for the broadest combination of all available non-glyphosate tactics including competition to be employed. 1. Use a strategy where all emergence events (germinations) in that season are controlled with something other than glyphosate. The model predicted that two non-glyphosate years out of five, or alternating glyphosate and non-glyphosate years, provided long delays in resistance if begun while resistance was still rare. 1. Act to delay resistance as soon as possible. It is not possible to tell what level of resistance is present in a population if it is not entirely resistant yet. Acting while resistance is still rare provides the best chance of delaying glyphosate resistance. 12

13 4.1 Residual herbicides and knockdowns Residual herbicides have some advantages for inclusion in a preventative strategy. In particular, they can offer some level of control on more than one flush of weeds, if the time of application and emergences coincide. However, the efficacy of a residual herbicide on any one cohort is often only average. This indicates that residual herbicides are unsuitable as the only nonglyphosate control if the aim is to slow or prevent resistance. Knockdown alternatives to glyphosate are less able to provide control over multiple cohorts. However, they can be timed to provide higher levels of control than residual herbicides. The table below shows several scenarios. Some relied on residuals alone and some included knockdown applications. Occasional summer cropping with two applications of residual herbicides within five years did not delay resistance at all, while four applications of residual herbicides provided only a small delay. Using both, residuals and non-glyphosate knockdowns in some summers (in crop and in fallow) always achieved better results than the application of residuals alone. Table 2: Modelling the effect of using residuals alone and with non-glyphosate knockdowns in several cropping scenarios Scenario Zero-tilled continuous winter cropping, glyphosate alone in summer fallows Early residual followed by glyphosate in continuous winter cropping, treatments applied in two out of five years Sorghum/wheat rotation 4x residual, 1x double knock every 5 years Sorghum/mung beans double-cropped/wheat rotation 5x residual, 2x paraquat every 5 years Years to reach 100% resistance Seed bank density at 100% resistant (seeds/m 2 ) Long-term seed bank* (seeds/ m 2 ) * Long-term seed bank refers to the density of weed seeds per square metre averaged over years of the simulation. 13

14 4.2 Summer cropping Often, growing a competitive summer crop offers benefits for delaying resistance. However, preventing resistance altogether is predicted to take more than just a competitive crop. For example, a simple sorghum/wheat rotation with two sorghum crops every five years and a single application of a residual herbicide per summer crop didn t offer any additional years of use of glyphosate on barnyard grass. A more highly mixed system of sorghum, wheat and mungbeans with the application of residual herbicides delayed resistance by four years. In continuous irrigated cotton, crop competition is predicted to delay resistance by six years, but the same is not true of dryland cotton grown every two years. Table 3: Modelling the effects of various summer cropping rotations on glyphosate resistance and seed bank density Scenario Sorghum/wheat rotation 2x residual every 5 years Sorghum/ mungbeans double cropped wheat rotation 5x residual every 5 years Continuous Roundup Ready Flex Cotton Irrigated, annual cropping Dryland, one crop every two years; glyphosate alone in summer fallows Years to reach 100% resistance Seed bank density at 100% resistant (seeds/m 2 ) Long-term seed bank (seeds/m 2 ) Timeliness of treatment Early intervention is more successful at delaying glyphosate resistance than waiting for resistance levels to increase in the population before introducing new tactics. Populations only remain small once resistance occurs if non-glyphosate tactics have already been in use for some years. In addition, the benefits of acting well before resistance dominates the population are also apparent for the long-term seed bank control. Table 4: The effect of delaying the start of an intensive prevention program until certain thresholds of glyphosate resistance have been reached. Scenario Continuous winter cropping: Double knock (glyphosate/paraquat) on first flush followed by paraquat, treatments applied in two out of five years after stated number of glyphosate-only years # years before starting prevention program Years to reach 100% resistance Seed bank density at 100% resistant (seeds/m 2 ) Long-term seed bank (seeds/m 2 )

15 4.4 Managing single or multiple flushes Strategies that attack all flushes in a year and include alternative herbicides or tillage are more successful at slowing or preventing glyphosate resistance than strategies that allow cohorts to be controlled with glyphosate only. Late-season cohorts treated sometimes with glyphosate and sometimes with nothing are a selection pressure for glyphosate resistance, even when the cohorts are relatively small. 4.5 Controlling survivors of glyphosate applications Deliberately controlling survivors of glyphosate applications can be done through separate applications of non-glyphosate tactics, or with an appropriately used double knock. Diligent and high efficacy survivor control after every glyphosate application is the best way to prevent resistance, but this is, of course, costly and not always possible. However, the closer the control of glyphosate survivors with alternative tactics is to 100%, the longer will be the delay in glyphosate resistance. Double knock Double knock is the use of two weed control tactics in close succession, so the second tactic controls the survivors of the first tactic. The time between knocks is usually one to ten days. The double knock can be two consecutive herbicides or any combination of weed control tactics including heavy grazing and cultivation. 15

16 5. Risks of cross and multiple resistance Cross resistance is defined as resistance to one herbicide that evolves as a consequence of the use of a second herbicide. Cross resistance can occur within an herbicide MOA Group, e.g. the use of a Group A fop herbicide can result in resistance to the applied herbicide and all other fop herbicides. Cross resistance can also occur across herbicide MOA groups, for example, use of a Group A fop herbicide may result in resistance to other Group A herbicides and some Group B herbicides. However, the latter occurs less commonly. Multiple resistance is defined as resistance to more than one herbicide in one plant and is caused by the evolution of multiple resistance mechanisms. It is a result of sequential use of herbicide groups, rotation of herbicide groups or mixtures of herbicide groups. For instance, the use of Group A herbicides triggers Group A resistance and is followed by the use of Group B herbicides which then causes Group B resistance in the same weed population. Glyphosate is the only Group M herbicide. To date, we have no evidence that glyphosate resistance results in resistance to any other herbicide group. It is also evident that the risk of cross resistance from glyphosate use is low. In contrast, the risk of multiple resistance due to glyphosate use is high. Glyphosate is used frequently for the management of weeds which are resistant to other herbicide groups, such as for crop-topping of Group A resistant wild oats and ryegrass in pulses. Persistent use of glyphosate as the sole management option for weeds with resistance to other herbicide groups will result in glyphosate resistance in the weeds already resistant to these other herbicides. One strategy adopted for the management of glyphosate resistant weeds, particularly in fallow situations, is to mix glyphosate with another herbicide or to clean up escapes with a different herbicide. If the same herbicide is used persistently to manage glyphosate resistant weeds, eventually resistance to that herbicide will also occur, resulting in multiple resistance. Weeds of the same species growing close together and treated with different herbicides may be a third way of establishing multiple resistance. For example, if glyphosate is used to control weeds along fence lines and other herbicides are used in the crop, resistance to the two herbicides might occur separately. If the weeds can then cross pollinate, individuals with multiple resistance can arise. To manage the risks of multiple resistance that includes glyphosate resistance, the adoption of non-chemical weed management strategies should be the first approach. It will be more difficult for weeds to evolve resistance to both glyphosate and a non-herbicide control method. Where non-herbicide tactics are not practical or not effective, care should be taken with the choice of alternative herbicides. Understanding the resistance risks of alternative herbicide groups is crucial. Multiple resistance is more likely to occur with high resistance risk herbicides, such as Group A and Group B herbicides and using herbicides from these groups as the sole management for glyphosate resistant weeds will result in multiple resistance. In addition, these herbicide groups do not make good partners with glyphosate in regards to resistance management due to widely existing resistance. The rotation of alternative herbicide management strategies will decrease the risk of multiple resistance and should be adopted wherever practical. Care should be taken where glyphosate and high resistance risk herbicides are solely used in close proximity to each other. Monitoring to detect potential resistance problems early will be crucial for effective management of resistance. 16

17 6. Monitoring and testing for glyphosate resistance Glyphosate resistance appears initially in a few isolated plants. These are often healthy or obviously re-growing and surrounded by dead plants of the same weed species. In the following seasons, patches of survivors can develop from these isolated plants if they are not prevented from setting seed. 6.1 Test timing Growers should consider testing for glyphosate resistance if: (a) their paddocks are at risk for resistance, and/or (b) there are survivors of a glyphosate application. Before testing is recommended to discount other common causes of herbicide failure by considering the following: Was glyphosate applied in conditions and at a rate that should kill the target weed? Did the suspect plants avoid herbicide contact or emerge after the spraying? Does the pattern of surviving plants suggest a spray miss or other application problem? Figure 3: Surviving glyphosate resistant awnless barnyard grass adjacent to susceptible plants killed by the herbicide (T. Cook). If glyphosate resistance is suspected, contact your agronomist or one of the researchers listed in Section 15 for advice. Also use one of the testing services listed in Section 6.5 for determining your resistance status. 17

18 6.2 Methods The two commercial tests for glyphosate resistance use either seeds and or whole plants. The seed test requires seeds to be collected from the suspect population and seedlings to be grown in pots. The plants will be sprayed with a range of glyphosate rates and their responses are compared with a known susceptible and a known resistant population. This method is generally very accurate and can test a large range of herbicides and rates. However, due to the seed dormancy the test duration is generally between 2-3 months and some suspect plants will have to continue to grow in order to collect seeds. The whole plant test, also known as the Quick-Test, is particularly useful for grass weeds and uses whole plants that are split into several pieces with 2-4 tillers and then trimmed and placed in pots. Once the plants are established and growing well they will be tested similarly to the seed test. The advantage of this method is a quick turn-around time for results of 4-6 weeks and there is no need to let suspect plants continue to grow to be able to collect seed. Growers and/or consultants can also conduct their own in-situ test, which involves applying test strips of glyphosate at a robust rate and higher rates to the suspect weeds in the paddock. Indications of glyphosate resistance are the survival of suspected weed species to both glyphosate rates, but other species are controlled by both rates. Resistant weeds sprayed at the higher glyphosate rates may have a set back but re-grow within one to two weeks. 6.3 Sample collection Seed or whole plants need to be sampled from a representative area of surviving plants. It is important to record the location of these collection sites on a mud map or with a GPS. For the seed test, several thousand mature dry seeds (about 1 cup of seeds for barnyard grass) from plants within the designated collection area have to be collected. It is important to gather only physiologically mature seed, not green underdeveloped seed, e.g. mature barnyard grass seed easily fall off the seed heads. The seed then needs to be sent to one of the testing services listed in Section 6.5. For the whole plant test, around 20 plants need to be collected and prepared as follows: Wash roots free of soil but do not wet the foliage; Wrap the roots in dry paper towel, place in a water-tight plastic bag and send by express post; The paper towel should contain a slight amount of water that will transfer from the washed roots to prevent the paper towel being too wet and therefore avoid rotting; Ten plants can be placed together in one bag; Larger plants can have their tops trimmed and discarded for easier logstics; and If the plants have 50+ tillers, fewer plants are required and some of the tillers can be removed and discarded. 6.4 Results 18 Even if the test is negative, but the paddock is considered high risk, appropriate preventive actions should be implemented by reducing the reliance on glyphosate and taking actions to stop seed-set on survivors of glyphosate spraying. If the test is positive for glyphosate resistance, an Integrated Weed Management (IWM) plan must be developed with the assistance of an agronomist. Alternate herbicides or non-chemical options are needed to replace glyphosate to control these resistant plants.

19 Care should also be taken to prevent further development of glyphosate resistance and prevent the spread of resistant seed to other parts of the paddock or other parts of the farm. 6.5 Seed Testing and Quick-Test service John Broster, Charles Stuart University, Wagga Wagga; (02) Peter Boutsalis, Plant Science Consulting, Adelaide;

20 7. Management of glyphosate resistance 7.1 Summer grasses Summer grasses are among the weed species with the highest potential to develop resistance to glyphosate. In Queensland and New South Wales there are now many populations of awnless barnyard grass and some populations of windmill and liverseed grass resistant to glyphosate. There are the following causes for the high susceptibility of summer grasses to glyphosate resistance: Reliance on glyphosate for the majority of grass control; Limited options for fallow control other than glyphosate; Limited post-emergent options for control in crop; High seed production of summer grasses; Grasses that are usually present in high densities; Limited use of cultivation as a weed control tactic; and Treatment of plants under hot dry conditions killing the susceptible proportion of the population while mildly tolerant individuals to survive. The suspected cases of resistant populations of barnyard, windmill and liverseed grass increase each year. There are also several populations of liverseed grass that are resistant to atrazine (Group C). Awnless barnyard grass (Echinochloa colona) Awnless barnyard grass emerges in multiple flushes from mid-spring to late summer and this extended timeframe throughout the season can often make the control of this weed difficult to control, as measures need to be employed throughout the season. However, the largest flush usually emerges with rain in late spring to early summer. Plants that emerge early in the season will, if allowed to mature, produce larger quantities of seed compared to those that emerge late in the season. It is therefore important that effective measures are applied especially during spring time. Liverseed grass (Urochloa panicoides) Liverseed grass tends to emerge in spring and early summer. Unlike awnless barnyard grass, it generally has one major flush with some minor flushes and effective control tactics need to be employed early in the season. Liverseed grass is very prone to moisture stress which can decrease the effectiveness of control tactics if applied during dry periods. Windmill grass (Chloris truncata) Windmill grass is a short lived perennial that commonly infests lighter textured soils. It is a summer active grass that will germinate under wet warm conditions. This weed becomes difficult to control once it produces tillers. Post-emergent options are limited, therefore the recommended approach is to consider pre-emergence tactics such as heavy grazing and cultivation first and control survivors with effective early post-emergence treatments. At the time of writing an APVMA permit was available for the fallow use of a Group A herbicide followed with a double knock with paraquat (Permit Number PER13460). 20

21 7.1.1 Strategic Integrated Weed Management (IWM) Know what the history of herbicide use is in each paddock. If glyphosate has been predominately used, it s time to change; Know what herbicides are effective on key weeds and aim for optimum control e.g. herbicide resistance testing; Rotate between herbicide groups; Use a selection of non-herbicide control options whenever the opportunity arises; Always monitor each control tactic thoroughly; Ensure survivors do not set seed to replenish the soil seed bank; Avoid the introduction or spread of weeds by contaminated seed, grain, hay, stock or machinery; Manage weeds in surrounding non-crop areas (e.g. fences, tracks, silos and sheds); and Review the completed control regime and adjust future management strategies accordingly Control in Fallow Achieving effective weed control in the fallow is critical as weeds have no competition from crops and the weed seed production is greater in fallow than in crop. This can have major impacts on glyphosate resistance evolution with surviving plants continuing to produce seed. It is therefore important that survivors of glyphosate applications are controlled by a herbicide with a different mode of action to glyphosate. One way to achieve this is to use the double knock technique. This will increase the control achieved and significantly reduce survivors from the glyphosate applications. The effectiveness of the double knock on a population of glyphosate resistant awnless barnyard grass is shown in the table below. Table 5: Control of glyphosate resistant awnless barnyard grass using the double knock (Bellata, NSW 2007, GRDC Project DAN00079) Herbicide Rate (L/ha) Rate (L/ha) Control (%) Knock One Knock Two glyphosate (450 g/l) paraquat (250 g/l) Spray.Seed glyphosate fb paraquat glyphosate fb paraquat glyphosate fb Spray.Seed glyphosate fb Spray.Seed Note: High levels of control in this trial were due to the application of herbicides to small awnless barnyard grass (very early tillering). 5 days between knocks. Using residual herbicides in fallows helps reduce the number of weeds that emerge, subsequently reducing the numbers potentially having to be controlled by glyphosate. The lower the numbers in the weed population sprayed the less is the chance of resistance evolving. Trials have shown that residual herbicides can be combined with double knock applications to reduce further weed emergence. 21

22 Table 6: Combining the double knock with residual herbicides can provide on-going control of awnless barnyard (BYG) and liverseed grass (LG). Weeds were at the 2 tiller stage at the time of spraying (St. Ruth, Qld 2008, GRDC Project DAQ00136) Knock 1 Knock 2 (7 DAK1 ) Control (%) (14 DAK1) New emergences (plants/m 2 ) (50 DAK1) BYG LG BYG LG Roundup CT* Paraquat Roundup CT Paraquat + Dual Roundup CT Paraquat + Flame Roundup CT + Dual Paraquat Roundup CT + Flame Paraquat * Rates: Roundup CT 1.6 L, Paraquat 1.6 L, Flame 0.2 L, Dual 2 L DAK1 = Days After Knock One Herbicide options There are a number of different herbicide modes-of-action (MOAs) that can be used to control awnless barnyard and liverseed grass, as outlined in Tables 7 and 8. The number and type of MOAs able to be used differs with each crop. For example growing cotton enables the use of up to 5 MOA groups on grasses, whereas only two MOAs are available for use in sorghum. Options for windmill grass are very limited as there are only two alternative registered herbicide options, being Factor WG (Group A) for post emergent use in pulses and Dacthal (Group D) for pre-emergent use in vegetables and cotton. However at the time of writing APVMA permit number PER13460 for fallow control of seedling windmill grass was granted. Having a broad enterprise rotation provides an opportunity to rotate herbicide MOA groups as well. Important points for herbicide options: Paraquat and paraquat + diquat are best applied with higher water volumes ( 100 L/ha), as it is essential to get good coverage on weeds. These are most effective on small grasses (no greater than early tillering stage); Barnyard grass control can be variable with atrazine, prometryn and fluometuron + prometryn; Imazapic, imazamox and imazethapyr have long plant back periods to a range of crops (see label); and Atrazine has a long plantback to cotton (see label). 22

23 23 Table 7: Registered herbicide options (other than glyphosate) for controlling awnless barnyard grass in crop and fallow.

24 24 Table 8: Registered herbicide options (other than glyphosate) for controlling liverseed grass in crop and fallow.

25 7.1.4 Non-herbicide options The pressure on herbicides to provide the majority of weed control can be reduced by utilising non-herbicide options where possible. This can be done in a number of ways, including the alteration of planting times, encouraging crop competition, cultivation, chipping and spot spraying. Using these methods in conjunction with herbicides may increase the effectiveness of the herbicides. Possible non-herbicide options and their use are listed in a table below. Table 9: Non-herbicide options for reducing the impact of summer grasses in crop and fallow. OPTION CROPS COMMENTS Time of planting Delayed planting of summer crops Sorghum, Maize Soybeans, Mungbeans The major flushes for barnyard grass and liverseed grass occur late spring/early summer. Delaying sowing until after theses flushes emerge allows other weed control options to be used such as double knock, and full disturbance planting. Some summer crops grow slowly in cool spring conditions and therefore don t compete well with weeds. Delayed planting until conditions are warmer will help increase the crops competitiveness. Early planting of winter crops Winter crops that aren t harvested until November/ December may have summer grasses that have already germinated. When harvesting has been completed, these grasses may have passed their optimum time to be sprayed. Choosing crops/varieties that can be planted earlier or are faster to maturity in order to be harvested before summer grass emergences enables them to be controlled when they are small. Crop/variety choice Sorghum Some crops and varieties are more competitive against weeds. Crops such as sunflowers have a low competitive ability and therefore are preferably not planted into fields with a heavy summer grass infestation. An evenly established, vigorously growing crop can compete strongly with weeds. Crop competition Row spacing/plant population Sorghum, Maize Soybeans, Mungbeans Decreasing row spacing creates less favourable conditions for competing weeds by increasing competition for moisture and light. Wider rows favour weed growth but allow inter-row cultivation. Weed-free periods Cotton, Sorghum, Maize, Soybeans, Mungbeans Keeping crops weed-free while they are getting established allows the crop to get a head start with all resources available. Once established it can then out compete weeds by shading, and taking resources with a larger root system. Cultivation Full-disturbance planting Sorghum For high weed pressure situations at the time of planting, using equipment that creates a full disturbance to kill weeds while planting is an option that reduces the reliance on herbicides. Strategic Cultivation of major flushes either before planting, in fallow or inter-row can significantly lessen the selection pressure on potential herbicide resistant weeds. Salvage Last resort for weeds out of control. Needs to be done before weeds have set seed or damage is already done. Inversion can be beneficial for small seeded species. Chipping/Spot spraying All Can be a very effective method to control survivors of herbicide application, particularly if they occur in low densities. Effectiveness is reliant upon good scouting to ensure escapes do not set seed 25

26 7.2 Fleabane Problem overview Flaxleaf fleabane (Conyza bonariensis) is a major weed burden to cropping in southern Queensland and northern New South Wales. It is also emerging as a problem in other cropping regions of Australia. For many growers, fallow weed control costs have increased markedly due to this weed. Some no-till farmers have needed to re-introduce cultivation as a last-resort control tactic where populations of flaxleaf fleabane were confirmed as resistant to glyphosate. Recent populations were found in zero or minimum-tilled paddocks in southern Queensland and northern New South Wales. The key to effective fleabane control is to attack all parts of the weed lifecycle and keep the seed bank to a minimum. Adopting an IWM strategy that includes chemical and non-chemical tactics for controlling seedlings and preventing seed production on survivors will result in substantially fewer fleabane problems and resistant populations in the future Identification There are seven Conyza species naturalised in Australia and flaxleaf fleabane is the most widespread. In a recent survey flaxleaf fleabane was also the only Conyza species found in cropping paddocks in northern New South Wales and southern Queensland. Flaxleaf fleabane grows up to 1m in height, has an erect stem covered with stiff hairs, and is generally multi-branched at the base. Leaves are grey-green, coarsely toothed and covered in fine hairs (refer to figure 4). This contrasts with tall fleabane (C. sumatrensis) which grows up to 2m and has a single stem with a pyramid shape inflorescence. Tall fleabane is commonly found on roadsides and in horticultural and other non-cropping areas. Figure 4: Conyza inflorescences L to R C. sumatrensis, C. bonariensis, C. canadensis (A. Storrie). 26

27 Table 10: Characteristics of the main three fleabane species in Australia Characteristic Flax-leaf fleabane (C. bonariensis) Tall fleabane (C. sumatrensis) Canadian fleabane (C. canadensis) Mature plant height (m) Stem branching Inflorescence shape Unbranched below flower head Lateral branches over-topping main stem Single stem Pyramid with lateral branches not over-topping main stem Single stem Pyramidal Floret colour White to pink Straw Cream Floret bracts Densely hairy Densely hairy Hairless Receptacle Smooth pitted Roughly pitted Smooth pitted Time of emergence Fleabane emerges when temperatures are between 10 and 30ºC, with the optimal temperature being around 20-25ºC. Seed will only germinate in the presence of light, and seedlings will emerge only in the top 1cm of soil, however some seedlings can emerge under low light conditions like under dense stubble. This explains partly why this weed proliferates in zero-tilled systems. In southern Queensland, fleabane emerges predominantly in autumn, early winter and spring, and there may be a limited emergence if conditions are mild during mid-winter and early summer. Seedlings that emerge in autumn grow slowly above-ground during winter and roots continue to grow deep into the soil to absorb available water. The development of such a strong root system during winter provides sufficient food reserve for rapid growth during the following spring which results in a difficult control of these over-wintered fleabane plants Fleabane seeds A single mature flaxleaf fleabane plant can produce an average of 110,000 seeds. Each seed carries its own pappus, or umbrella of light hairs and this enables the seed to be easily lifted and dispersed by wind over considerable distances. Even though most fleabane seeds lose their viability within months in the soil seed-bank, a small percentage can persist for several years, particularly if seeds are buried below the surface soil. Such seed characteristics make fleabane a major weedy problem, and highlight the importance of controlling all plants to prevent major replenishment of the seed-bank Strategic management approach For paddocks infested with fleabane, tackling the problem requires a strategic approach based on good agronomy and uses a mix of weed control tactics Use an IWM strategy that combines chemical and non-chemical tactics to deplete the seed bank, control seedlings, stop seed production and seed rain, and prevent introduction of new seeds will significantly reduce the impact of this weed problem. 2. Benchmark the current fleabane impacts and paddock situation weed density, distribution, herbicide history. 3. Closely monitor fleabane emergence throughout the cropping system to

28 ensure effective treatment of young seedlings. 4. Use a variety of chemical and non-chemical control tactics. 5. Rotate between different herbicide groups, alternatively tank mix with effective herbicides from different mode of action groups it is important to use robust rates for both herbicides in the mix. 6. Aim for maximum effectiveness to keep weed numbers low the primary aim of weed control is to minimise their impact on productivity, and resistance is much less likely to develop in paddocks with fewer weeds than in heavily infested paddocks. 7. Ensure survivors do not set seed and replenish the soil seed-bank consider using the double knock tactic, particularly for dense infestations and larger weeds. 8. Avoid introduction or spread of fleabane and manage weeds in surrounding non-crop areas to minimise risk of seeds moving into adjacent paddocks. 9. Review the completed control of fleabane to adjust future management strategies accordingly Control tactics Seed bank depletion Research has shown that a number of residual herbicides provide good control of fleabane seedlings for several months in fallow, pre-planting and during the crop phase. As most residuals do not control emerged fleabane, they need to be applied to a clean paddock or with an effective knockdown herbicide or double knock. The Group C triazine was very effective when applied in a winter/spring fallow prior to sorghum, and rainfall received within 1-2 weeks of spraying enabled the incorporation of the herbicide into the soil to control germinating seed. In addition, Group C urea (used prior to cotton), Group B sulfonylurea (used prior to wheat) and Group H isoxaflutole (used prior to chickpea) were very effective in reducing emergence of fleabane for several months. Figure 5 shows the level of control when mixed with a double knock of glyphosate + phenoxy or glyphosate + Tordon 75-D. Interestingly, there was good residual control with the Tordon 75-D component of the double knock, providing 88% control over approximately six months. Research has also shown that tillage operations alter the distribution of fleabane seeds in the soil profile and subsequent emergence of the weed and a light harrowing and zero till promoted greater emergence than chisel and disc ploughing. Control in fallow A range of herbicides, mixes and sequential applications provide good seedling control in fallow, however weed size, age, density and growing conditions at spraying greatly influence the performance of the treatment. Furthermore, efficacy of many herbicides, such as amitrole, has been proven to be very slow with visual symptoms appearing as late as one month after application and death at six to eight weeks. Correct timing of herbicide application is essential for a good IWM program. It is crucial to apply herbicides when the plant is a small rosette, particularly prior to stem elongation, as control efficacy declines as plants mature. The table below provides the treatment results of a range of registered herbicides applied to one- and three-month old plants, with the overall efficacy reduced from 92% for one-month old weeds to 77% for three-month old weeds. 28

29 Consistently the most effective treatment is the double knock technique, particularly the application of glyphosate + Tordon 75-D followed in seven days by Spray.Seed. For these fallow treatments to be effective, robust rates and high water volumes of around 100 L/ha for paraquat products are needed. This applies particularly for dense populations and high stubble levels. Ideal follow-up times for Spray.Seed and paraquat products are 5-7 days after glyphosate application. Full control of fleabane throughout the winter fallow can greatly minimise infestations in following spring-sown crops. Figure 5: Cumulative emergence of fleabane over six months following application of a double knock using glyphosate + phenoxy or glyphosate + Tordon 75-D followed by a residual mixed with Spray.Seed in the second knock (southern Queensland, GRDC Project UQ00055) 29

30 Table 11: Efficacy of knockdowns in a winter fallow in four field experiments, measured at six weeks after treatment. The range of efficacy across the experiments is in brackets (Darling Downs, GRDC Project UQ00055) Herbicide Weed control (%) One month old Three month old Glyphosate + phenoxy 84 (62-100) 76 (63-96) Glyphosate + Tordon 75-D 93 (86-99) 84 (62-98) Glyphosate + phenoxy fb Spray.Seed 96 (93-100) 93 (87-97) Glyphosate + Tordon 75-D fb Spray.Seed 99 (97-100) 97 (92-100) Glyphosate + phenoxy fb Alliance 96 (92-99) 90 (78-100) Phenoxy fb Spray.Seed 97 (97-98) 83 (68-97) Phenoxy # 88 (81-95) 53 (48-57) Amitrole # 90 (84-95) 96 (95-97) Spray.Seed # 84 (78-89) 22 (13-30) Mean fb = followed by a 7 day interval # = applied in only 2 of the 4 field experiments Control seedlings in crop Efficient in-crop control of fleabane will greatly reduce problems due to this weed in the following fallow. However, no selective herbicides effective on fleabane are currently registered. Research shows that fleabane is susceptible to several Group I herbicides used in wheat which also could be useful for controlling the late autumn and early winter flushes of fleabane. In two pot experiments Group I herbicides gave excellent control (95 100%) for small or young weeds treated under optimal soil moisture conditions. However, efficacy was reduced by an average of 8% when young weeds were moisture stressed at spraying, and treating larger moisturestressed weeds resulted in an unsatisfactory control with only 57%. In the field a delay of spraying by two weeks resulted in increased weed age and moisture stress which reduced the overall efficacy of Group I herbicides from 87% to 48% control. However, crop competition is another useful tactic to suppress fleabane growth and seed production. Figure 6 shows 90% reduction in the number of fleabane heads when wheat was grown in narrower rows and in higher population. Effective control of dense infestations is easier achievable using a combination of competitive wheat crops and spraying small weeds under good soil moisture conditions. 30

31 Figure 6: Impact of crop competition (wheat) on flowering heads of fleabane in wheat at two row spacings and two crop populations (southern Queensland, GRDC Project UQ00055) Stop seed production and seed rain Many knockdown treatments do not give full control of fleabane and as prevention of seed set on survivors an IWM plan is essential, including regular follow-up actions. The use of double knock (see Section 1) can be very effective. This tactic can achieve almost 100% weed control, thus significantly reducing the impact of weeds on following crops. 31

32 7.3 Annual Ryegrass Crop and fallow situations Effective control of glyphosate resistant annual ryegrass requires a well planned approach including herbicide resistance testing to determine which herbicides are effective. This is recommended for every affected paddock as there may be significant differences in resistance levels between paddock samples. Ryegrass might also be resistant to more than one herbicide mode-of-action (MOA). Annual ryegrass seed is short lived in the soil and two years of no weed seed set results in a adequate decline of the original seed bank in the third year. However, a light infestation with only low numbers of plants setting seed can quickly increase in density, which is due to substantial seed production capability of this weed, particularly in fallows. While good in-crop management of glyphosate resistant annual ryegrass is always required, it is often easiest to deplete the weed seed bank in the fallow as: It s much easier to monitor the success of treatment, as there is no crop present; Many annual ryegrass populations in Australia have resistance to other herbicide MOAs commonly used in crops; Crops can intercept a significant proportion of herbicide before contact with weeds, thus reducing spray effectiveness; Timeliness of treatments used in fallows is not restricted by crop stage or herbicide selectivity; and A WeedSeeker (camera detector) (APVMA Permit PER11163) enables a wider range of rates of some products (e.g. paraquat) to be used in fallow. In time, this permit may be extended to other states. Furthermore, herbicide companies are likely to register the WeedSeeker technology as a label use pattern Strategic approach Small patches It is recommended to thoroughly map the infestation(s). Some patches of glyphosate resistant weeds can exist as small infestations, often 50 to 100 m 2, and separate management of those to the rest of the paddock should be considered. It may require sacrificing crop production in small areas; however, if managed properly, the long term benefits will outweigh the short-term cost as the chances of successfully eradicating glyphosate resistant annual ryegrass decreases as infestation size increases. Further, managing small patches of glyphosate resistant annual ryegrass requires less effort and has a lower cost compared to large infestations. Therefore, it is important to detect glyphosate resistance as soon as possible. This requires regular and thorough monitoring of glyphosatetreated areas (cropping and non-cropping). If suspect patches are detected, samples of live plants should be sent for Quick-testing (See Section 6) and the remaining plants controlled, ensuring that no new seed is returned to the soil. The intense management of small infested patches will often result in the substantial reduction of annual ryegrass densities. Then the hand weeding of the survivors becomes practical and may be the most cost-effective tactic. 32

33 Figure 7: A farmer hand-weeding glyphosate resistant annual ryegrass (T. Cook). Glyphosate resistance often develops along fence lines and it is common to find glyphosate resistant annual ryegrass creeping from fence lines into cropping areas. If this occurs, it may be best to sacrifice this area of the crop, such as cutting it for hay followed by an herbicide application to control any re-growth. Larger infestations If the size of the glyphosate resistant infestation has increased, a broad scale control approach will be needed and the chances of eradicating glyphosate resistant annual ryegrass are substantially lower. However, it must be noted that large dense infestations can be managed to levels where the weed density is very low but widespread and small patch control tactics can be utilised again. Economic justification for controlling sparse, yet widespread glyphosate resistant annual ryegrass is often a contentious topic for many farmers and agronomists. The cost of hand weeding sparse populations over large areas is likely to be prohibitive. Weed detector technology can augment the control of weeds in such situations minimising herbicide and labour costs. A comprehensive herbicide resistance test provides knowledge of which herbicides are still effective. 33

34 Figure 8: Widespread glyphosate resistant annual ryegrass infestation at Spring Ridge, NSW, following 2 L/ha glyphosate (450 g/l) (A. Storrie) Effective treatments in fallow In general an integrated approach that combines chemical and non-chemical tactics will provide more sustainable and effective control. Non-chemical control - Cultivation The ideal cultivation control technique for glyphosate resistant annual ryegrass comprises of the full disturbance and the shallow working of a drying soil. The following points are detrimental to control with cultivation and need to be considered: If a hard setting soil is too dry, an effective level of soil disturbance may not be achieved and damage to the soil structure may result; Working wet soils will lead to smearing and compaction, as well as transplanting weeds in clods; and Deep cultivation with tined or disc implements can bury viable seed throughout the soil profile, prolonging seed longevity in many weed species compared to a no-till situation where weed seed is largely left exposed on the soil surface. Non-chemical control - Autumn tickle Shallow cultivations in autumn will stimulate the seed bank to germinate. The aim of maximising weed germination is to provide the opportunity to apply effective pre- and post-emergence tactics to lower the weed seed bank faster. However, timing of the autumn tickle is critical. It should be scheduled to when the peak germination flushes of annual ryegrass and significant rainfall are expected - usually from April to May. 34

35 The autumn tickle is normally used in conjunction with delayed sowing, and is often best suited to barley, field peas and chickpeas, as those crops have a later optimum sowing time. Non-chemical control - Mouldboard ploughing This technique aims to bury most of the seed bank to a depth where annual ryegrass cannot emerge. Optimal emergence depth for annual ryegrass is approximately 2cm; however mouldboard ploughing aims to bury seed greater than 20cm. The soil should not be disturbed for over 10 years after mouldboard ploughing, as tillage will bring viable seed to the surface again. Seed longevity of annual ryegrass near the surface is very short (usually 2 to 3 years), but at depth this period will extend greater than 5 years. Mouldboard ploughs fitted with skimmers have been used to good effect in the lower draft sandy soils of Western Australia. They are employed to skim the weed seed of the soil surface and to put it at the bottom of the furrow. The high cost of such operations can be offset by solving a soil degradation problem such as non-wetting or incorporating lime for acid soils at the same time. Non-chemical control - Burning crop residues This tactic can lead to highly variable results, which depend on stubble loads, placement of seed and type of stubble. Levels of control can vary from 35 to 99% control. Used extensively in WA, header heights are set low (15cm) and header rows are concentrated to increase the fuel load to obtain a hot and slow burn in the following autumn as this is needed to effectively kill the seed. In areas where significant levels of summer rainfall might occur this tactic may not be effective as windrows may not burn to the ground. Chemical control - Post-emergence A range of chemical options are available for control of emerged glyphosate resistant annual ryegrass and growers have the following options: Blanket spray with an effective (non-glyphosate) herbicide; Use the double knock technique; and Apply non-glyphosate herbicides through a WeedSeeker (Pesticide Permit No PER11163). Chemical control - Pre-emergence Residual or pre-emergence herbicides can often result in high control levels of glyphosate resistant annual ryegrass. However, less satisfactory levels of control can be experienced when conditions are dry after spraying. Despite the potential for variable control, it is recommended that a pre-emergence herbicide be applied to control the first few flushes of weeds. Excellent pre-emergence control should reduce the population of annual ryegrass and greatly lessen the resistance selection pressure for subsequent post-emergence chemical treatments. The table below summarises which herbicide categories exhibited reliable useful levels of control of glyphosate resistant annual ryegrass in trials. 35

36 Table 12: Pre-emergence control of glyphosate resistant annual ryegrass, shown by herbicide sub-grouping in order of most effective to least effective (Liverpool Plains, NSW, Project DAQ527) Herbicide MOA Group B (sulfonylureas) Group C (triazines) Group K Group B (imidazolinones) Group D Example - active ingredients chlorsulfuron, triasulfuron atrazine, simazine metolachlor imazapic trifluralin Note: All these herbicides resulted in >80% control following suitable post-spraying rainfall. Please note that this Liverpool Plains population did not have resistance to herbicides shown above. Ensure a comprehensive herbicide resistance test is undertaken prior to planning management of glyphosate resistant annual ryegrass. Knockdown alternatives to glyphosate Apart from glyphosate, there are few registered knockdown herbicides effective on glyphosate resistant annual ryegrass. Only products containing paraquat, paraquat + diquat (Group L herbicides) or paraquat + amitrole (Groups L + Q) are registered and are effective. Research has shown that these products are ideally suited to treating glyphosate resistant annual ryegrass no later than the early tillering stage. Relying upon Group L herbicides as an answer to managing glyphosate resistance will increase the risk of developing Group L resistance. Therefore, always monitor areas post-spraying and ensure survivors of the herbicide application do not set seed. Cultivation, hand weeding or weed detector spot treatment can be used to treat these survivors. Figure 9: Annual ryegrass at the early tillering stage (A. Storrie). 36

37 Double knock technique Although glyphosate resistant annual ryegrass may be present in fallow paddocks, with the double knock technique glyphosate will be used to control other weed species and the susceptible portion of the annual ryegrass population. However, an herbicide with a different MOA must be used between 3 to 7 days later to control the glyphosate resistant individuals. The standard follow-up treatment (second knock) is paraquat or paraquat + diquat (Group L). Having two different tactics following in close succession limits the chances of survivors from the first treatments to continue to survive and to produce seed. Rules of thumb for double knocking of glyphosate resistant annual ryegrass: Never use glyphosate as the second knock it won t work; Paraquat is about 10% more effective than paraquat + diquat mixes at the same rate on glyphosate resistant annual ryegrass; Aim to have the first knock applied to glyphosate resistant annual ryegrass no later than the early tillering stage (DC 14); As the annual ryegrass growth stage approaches mid tillering, increase the rate of Group L herbicide to maintain the level of control (Refer to herbicide label of rate recommendations, and the table below); Residual herbicides can be mixed with the Group L herbicide (second knock) to provide long term control. Check labels to determine the plant back requirements for residual herbicides; The second knock using Group L herbicide should be applied within 1 to 7 days. If rainfall prevents the application of the 2nd knock and the glyphosate resistant annual ryegrass gets beyond mid-tillering stage, consider alternatives to Group L herbicides (WeedSeeker with higher herbicide rates or cultivation) as Group L herbicides will not reliably achieve high levels of control at this stage; and The second knock does not have to be a Group L herbicide. It can be any tactic, including cultivation, which attains a very high level of control. Table 13: The effect of increasing glyphosate resistant annual ryegrass growth stage and increasing paraquat or Spray.Seed rates on control, after an initial application of glyphosate (450 g a.i./l) at 1.2 L/ha (Spring Ridge, NSW Project DAQ527) Glyphosate resistant annual ryegrass growth stage at second knock Rate of paraquat used and % control Rate of Spray.Seed used and % control 2 ½ leaf and early tillering (DC 12.5) 1.5 L/ha L/ha 96 3 leaf and early tillering (DC 13) 2.0 L/ha L/ha 96 Early to mid tillering 2.0 L/ha L/ha 95 Mid tillering 2.5 L/ha L/ha 94 37

38 Figure 10: Glyphosate resistant annual ryegrass controlled extremely well by double knocking in small plot experiment, Liverpool Plains, NSW. NOTE untreated plot to the right (A. Storrie). Weed detector technology In 2011, the APVMA issued a permit that gives growers access to a wider range of herbicides and rates in fallow when using a WeedSeeker machine to control annual ryegrass. This technology is best suited to managing glyphosate resistant annual ryegrass on larger properties, particularly with low plant densities and when hand weeding or cultivation is not feasible. However, the area to be sprayed must not exceed 30% of the paddock area. Twelve different herbicides are listed on the permit that control annual ryegrass, some being non-residual and others with short or longer term activity in the soil. Some herbicide rates have been increased to allow control of larger and/or stressed weeds. For example the paraquat or Spray.Seed rates range from 3 to 4 L/ha (using a set application volume of 100 L/ha). This exceeds the top label rate of 3.2 L/ha for a full spray application in fallow. Previous research has found herbicides such as paraquat or Group A herbicides to be extremely useful options to control glyphosate resistant grasses in fallows. The new permit will allow the use of these herbicides at robust rates. It will be in force until 28 February It has to be noted that the application of Group A herbicides in fallows come with the high risk of resistance development to Group A herbicides. Appropriate warnings are listed on the permit to prevent or delay the evolution of Group A resistant weeds. In summary the WeedSeeker permit now provides growers with the following benefits: Reduced herbicide costs, especially on sparse patchy infestations; Better management of glyphosate resistant weeds in fallows; and Better control of harder to control weeds, whether it is due to natural herbicide tolerance, size or moisture stress. 38

39 Figure 11: WeedSeeker in action (Crop Optics P/L) Effective treatment in crop An integrated management approach that combines chemical and non-chemical tactics will provide more sustainable and effective control for annual ryegrass. Glyphosate is normally used prior to sowing the crop as a knockdown application and this applies strong selection pressure during the cropping phase and will happen in most years. However, in some crops it can also be used for stopping weed seed set, and in cotton as an inter-row treatment. Effective strategies for management of glyphosate resistant annual ryegrass in crop involve the use of double knock applications, crop competition where appropriate, alternative herbicides in crop where effective and seed set control. Implementation of a planned approach combining these tactics over several years can rapidly reduce the amount of glyphosate resistant annual ryegrass present. Double knock techniques such as glyphosate followed by a paraquat-based herbicide or two applications of a paraquat-based herbicide or glyphosate followed by full disturbance cultivation, not only control any glyphosate resistant individuals, but also greatly reduce the number of annual ryegrass plants that have to be managed in crop. This reduces the pressure applied to crop selective herbicides. It has to be noted that over-reliance on paraquat could lead to paraquat resistant weeds, so other tactics need to be included. Pre-emergent herbicides can also be effective at reducing the weed population that has to be managed in crop and therefore wherever practical, a pre-emergent herbicide that is effective on annual ryegrass should be used. These include: trifluralin (Group D), Boxer Gold (Group J + K), triallate (Group J) and pyroxasulfone (Sakura, Group K). 39

40 Pre-emergent herbicides require moisture to work effectively, so dry conditions will reduce the control of annual ryegrass. Over-reliance on any one pre-emergent herbicide is likely to lead to resistance to that herbicide and different pre-emergent herbicides should be used in alternate years to slow resistance. Crop competition is another effective strategy for managing glyphosate resistant annual ryegrass. The glyphosate resistant ryegrass is less fit and produces less seed than susceptible ryegrass and applying greater crop competition to glyphosate resistant ryegrass will further reduce its seed production. However, crop competition is only an effective strategy in cereals, and to a lesser extent in canola, and can be achieved by growing a more competitive crop, a more competitive cultivar and increasing the crop seeding rate. As a result of their lower seed production in crop, glyphosate resistant annual ryegrass is an ideal target for seed prevention and destruction tactics. Such tactics include hay, silage, crop-topping (not with glyphosate), chaff carts, windrow burning and the Harrington Seed destructor. Refer to Section 10 - Seed destruction for more detail. When first identified, glyphosate resistant annual ryegrass is normally present in small patches and in many cases, only the area infested with resistant ryegrass needs to be treated. Patch management though can be problematic as glyphosate resistant individuals may located of up to 50m away from the main infestation and may become the focus of a new infestation. Careful monitoring is therefore essential for early detection of these new patches Roundup Ready canola The introduction of glyphosate tolerant Roundup Ready canola has allowed new use patterns for glyphosate in the cropping rotation. Roundup Ready canola presents an increased risk for the development of resistance compared to most other crops in that glyphosate can be used in crop. This exposes more of the weed population to glyphosate than occurs solely from a presowing use of the herbicide. When growing Roundup Ready canola, use the Crop Management Plan. This provides guidance on how to maximise the crop yield and herbicide efficiency while offering strategies to reduce the glyphosate resistance risk. It is important that a risk assessment is conducted prior to deciding to sow Roundup Ready canola in a paddock. If the paddock has a medium or high resistance risk, strategies to reduce that risk should be included in the management plans. Paddocks known to contain glyphosate resistant weeds are not suited to Roundup Ready canola. Where practical, Roundup Ready canola should be planted into paddocks with lower weed numbers. A pre-emergent herbicide that controls grass weeds is desirable in Roundup Ready canola crops, especially if clethodim resistance is suspected or confirmed, and should be used in all situations where high grass weed numbers are expected. Roundup Ready herbicide applications should be planned ahead to ensure an application is made at the 6-leaf crop stage to provide the best herbicide coverage prior to canopy closure. 40

41 Figure 12: Roundup Ready canola should not be sown in paddocks with high annual ryegrass populations such as seen here (C. Preston). As mentioned before, monitoring crops after a glyphosate application is vital. Roundup Ready canola has proven to be a good way of identifying glyphosate resistant weeds that are already present in the paddock. However, there are limited options for the control of weeds appearing late in canola crops, hence decisions regarding remedial actions need to be made early. Hybrid canola varieties have improved competitive abilities compared with other canola varieties. Unfortunately, the crop canopy opens after flowering, allowing grass weeds to produce significant amounts of seed. In this situation, swathing canola can reduce the seed set of many weeds. Figure 13: Hybrid canola cultivars are more competitive than conventional cultivars and suppress early annual ryegrass growth (C. Preston). 41

42 Management options There are limited options for the control of weeds appearing late in canola crops, with much of the work to reduce glyphosate resistance risks needing to be done in the years before and after growing Roundup Ready canola. One of the best strategies is to burn narrow windrows in the Roundup Ready canola stubble. This lessens the selection pressure in the year of the crop and addresses any potential survivors after glyphosate application. Other strategies that reduce weed seed banks, such as cutting for hay, using chaff carts and burning windrows, can be employed in the year before growing Roundup Ready canola in order to reduce the weed seed bank and the risk of resistance. In the year after growing Roundup Ready canola, the treatment with a nonglyphosate knockdown herbicide will decrease the glyphosate resistance risk and aid the control of any potential glyphosate resistant weeds, as well as Roundup Ready canola volunteers. Wherever practical a competitive crop should be planted to reduce the seed set of any glyphosate resistant weeds that may be present. Further reduction of the seed bank can be achieved with the utilisation of weed seed set control practices, such as a chaff cart, windrow burning or hay. The level of risk of glyphosate resistant weeds from growing Roundup Ready canola depends on past glyphosate use patterns and the frequency with which Roundup Ready canola is grown in the rotation. Tight rotations of Roundup Ready canola of less than 4 years apart will greatly increase the glyphosate resistance risk and should be avoided. Glyphosate resistance risk can also be decreased by reducing the amount of dependence on glyphosate in other crops in the rotation. While a well-managed Roundup Ready canola crop can be a useful weed management tool in the rotation, a poorly managed Roundup Ready canola will significantly increase the risk of glyphosate resistance Fence lines Glyphosate resistance is becoming an increasing problem on fence lines and in other un-cropped areas of the farm. Currently, there are nearly 90 known sites of glyphosate resistance on fence lines, crop margins or driveways on farms. Glyphosate resistance most commonly evolves in areas where glyphosate is used intensively as the only weed management tactic and where there is no competition from other vegetation which applies to fence lines and other un-cropped areas. Glyphosate resistant weeds on fence lines present a major problem as weeds can easily move from the fence line into a cropped area. Harvesting equipment in particular can drag weed seed from the edge of the crop and move it further into the paddock. Another important motivation to keep fence lines free of weeds and other vegetation is the potential creation of a habitat for pests such as snails. Weeds in these areas can also create a fire risk. 42

43 Figure 14: Uncontrolled glyphosate resistant weeds on the fence line can move into the paddock (C. Preston). Management options A number of strategies are available for the management of weeds in non-cropped areas of the farm to suit different situations, various desired outcome and potential erosion risk. Slashing and mowing can be effective tactics to manage vegetation height and to reduce fire risks. Some growers will plant a crop close to the fence and then cut the outside lap of the crop for hay as a strategy to reduce the fire risk and the invasion of weeds into the crop. This strategy is very effective and lessens the herbicide applications to the area immediately adjacent to the fence. However, this strategy requires the appropriate equipment to be available and an investment in time. Slashing and leaving the slashed material on the surface can create mulch that will inhibit future germination of weeds in the area, but this material can harbor pests and create difficulties with farm operations and is not suitable for areas with high amounts of vehicle movement. Cultivation of the area immediately adjacent to the fence line during spring is another option for managing fire risks, pests and the risk of weed invasion of the crop. Cultivation will control any glyphosate resistant weeds that appear on the fence line, although leaving the soil bare and prone to erosion, which can be a particular problem for light soils. Cultivation however destroys the soil structure and creates problems for movement of farm vehicles and equipment and therefore is not suitable for areas with high levels of vehicle movement. One option that may be effective in some situations is to plant an alternative competitive species in the area. Perennial native grasses or other native low- 43

44 growing species would be most suitable. However, many of these species are not very tolerant to herbicides used in farm management and over time the native plantings will thin out and weeds will invade. These native plantings can also harbor pests, such as snails. They may also need additional management, such as mowing, to retain a suitable height. Herbicides may be the preferred option for controlling unwanted vegetation along fence lines and in other un-cropped areas of the farm, although solely relying on glyphosate will not be effective in managing glyphosate resistant weeds and the problem is likely to spread. There are several other herbicides that have registrations for use in non-cropped areas of the farm. Recent research has established that a mixture of a knockdown herbicide with a residual herbicide provides the most effective management of glyphosate resistant weeds. Where glyphosate resistance has not yet occurred or where weed numbers are low, mixtures of glyphosate with a residual herbicide may be the most appropriate option. However, this is likely to be a short term option. Paraquat-based herbicides such as Gramoxone, Spray.Seed or Alliance mixed with residual herbicides have proved to be more effective at controlling glyphosate resistant weeds on fence lines. Two applications of Spray.Seed applied 14 days apart or Amitrole T at 6 L/ha mixed with paraquat-based herbicides have also proven to be effective. Application of a residual herbicide early in the season is likely to reduce weed emergence along fence lines and may be another useful strategy. Table 14: Herbicides that control grass weeds and which are registered for use on fence lines Knockdown herbicides and herbicide MOA Residual herbicides and herbicide MOA glyphosate (Group M) simazine (Group C) paraquat, diquat (Group L) imazapyr (Group B) glufosinate (Group N) 2,2-DPA (Group J) amitrole (Group Q) ethofumesate (Group J) pine oil (Group Z) MSMA (Group Z) Figure 15: Control of weeds along a fence line with a double knock of glyphosate followed by paraquat + amitrole (C. Preston). 44

45 7.3.7 Vineyards Glyphosate resistant annual ryegrass has occurred in many vineyards, particularly in South Australia and Western Australia. Current vineyard weed management typically includes a mown sward or winter cover-crop between the vine rows and a bare area immediately under the vines. Weeds in vineyards are managed to reduce frost risk, water consumption and the impact on vineyard management operations and consequently there is a preference for bare ground immediately beneath vines. This in particular applies to glyphosate resistant annual ryegrass. Figure 16: A vineyard with a winter faba bean cover crop and glyphosate applied under the vine (C. Preston). Common practice in vineyards is the use of a glyphosate product during winter to control weeds under the vines. This creates a risk for the evolution of glyphosate resistant annual ryegrass, and other winter weeds. As outlined before, glyphosate resistance occurs in situations where the herbicide is used intensively, no other weed management is employed and there is no competition to reduce surviving weed seed set, and the under-vine area of vineyards fits all of these criteria. It has to be noted that if the mid row of the vineyard is mown, there is a risk of movement of glyphosate resistant weed seeds from one area of the vineyard to others. Figure 17: Annual ryegrass surviving glyphosate treatment in the under-vine area (C. Preston). 45

46 Management options While there are many possible management options for glyphosate resistant annual ryegrass, several of these may be difficult to employ in a vineyard due to its setup, current vineyard management and the availability of equipment or skilled personnel. Therefore, different strategies will suit different conditions. Under-vine tillage is an old weed control tactic that has been phased out of many vineyards with the advent of modern herbicides. Under-vine tillage effectively controls many weeds, although the disturbance can encourage weed seeds to germinate. Other problems of under-vine tillage include the potential damage of vine roots and vine stems as well as soil compaction and the reduction in water infiltration caused by high traffic during the control action. However, the issues can be managed by employing appropriate equipment and a skilled operator for undervine tillage Mulches can also be used to reduce weed growth in the under-vine area. Mulches work best if they can stop all light from reaching the soil. However, mulches are expensive, difficult to apply and need to be managed as they break down. Mulches, depending on their type, may not be effective against weeds with wind-borne seed. Flaming and steam weeders can be very effective at controlling shallowrooted seedlings of broadleaf weeds. Flaming and steam weed control requires the purchase of new equipment and, depending on equipment set-up and number of passes required throughout the season, can be expensive to operate. Alternative herbicides will likely be the first option investigated if glyphosate resistance evolves in vineyards. Unfortunately, there are a limited number of alternative herbicides are registered and effective for annual ryegrass control. There may also be restrictions from end users on the products that can be used on grapes or on the timing of the applications of these products. Herbicide labels should always be consulted prior to applying a product to determine if the product is registered for the use and the rate at which it can be applied. Glyphosate mixtures with other herbicides, such as amitrole, may also be effective at controlling glyphosate-resistant annual ryegrass adequately in situations where the weed population is low, weeds are small and robust rates of the mixing partner are used. However, over time, this strategy will result in an increase of glyphosate resistance and hence should be seen as a stop-gap strategy. Paraquat-based herbicide products and mixtures (paraquat + diquat or paraquat + amitrole) control glyphosate resistant annual ryegrass well, as long as the weeds are not too large. These products have proven to be effective in several situations where glyphosate resistance has evolved. Glufosinate-based herbicide products are generally less successful at controlling glyphosate-resistant annual ryegrass. These herbicides work less effectively during cool conditions in winter and re-treatment is often necessary. However, glufosinate works well in spring as the weather warms and can be used effectively to limit seed set of annual ryegrass. Several grass-selective herbicides (fluazifop-p-butyl, haloxyfop-r-methyl) are registered for use in vineyards. These all control annual ryegrass and could be mixed with other herbicides to improve grass weed control. However, a significant portion of the annual ryegrass in grain-growing regions is resistant to these herbicides and resistance would be expected to have transferred to vineyards as well. Soil residual herbicides can also control annual ryegrass, although their use is not without difficulty. Trifluralin, pendimethalin and oryzalin need to be incorporated by rainfall or irrigation to work. Simazine is restricted for use with older vines and 46

47 damage may occur if used on young vines or in light soil types. Advice is provided on product labels about how best to use these products. Research results indicate that a mixture of knockdown herbicide products, such as paraquat + amitrole, mixed with a soil residual herbicide, such as pendimethalin, provides the best and most reliable control of glyphosate resistant annual ryegrass. A combination of chemical and mechanical tactics for weed control is likely to provide the most long lasting solution to herbicide resistance in vineyards. Over reliance on other herbicide products will inevitably lead to resistance to those products as well. When glyphosate resistance first appears in vineyards it is likely to consist of only a small number of plants in an isolated area and quick action to remove those few plants will limit the spread of the problem. Table 15: Herbicides registered for the control of annual ryegrass in vineyards Post-emergent herbicides and herbicide MOA Pre-emergent herbicides and herbicide MOA glyphosate (Group M) simazine (Group C) glufosinate (Group N) pendimethalin (Group D) paraquat (Group L) trifluralin (Group D) paraquat + diquat (Group L) norflurazon (Group F) amitrole (Group Q) napropamide (Group K) amitrole + paraquat (Group Q + L) oxyfluorfen (Group G) fluazifop-p-butyl (Group A) haloxyfop-p-methyl (Group A) Figure 18: Demonstration of glyphosate resistant annual ryegrass control with a combination of paraquat, amitrole and pendimethalin (C. Preston). 47

48 7.4 Seed destruction Weed seed production and selection of resistant weeds The development of glyphosate resistant annual weed populations is dependent not only on the selection of resistant plants through in-crop herbicide application, but also on these plants returning viable seed to the seed bank. In any large population of annual weeds there are naturally-occurring herbicide resistant individuals. Therefore, whenever an effective glyphosate dose is applied, the naturally-occurring resistant individuals survive. However, selection for glyphosate resistance is only completed when viable seeds return to the seed-bank and the selection for herbicide resistance in any weed population can be prevented by stopping seed set. A follow-up control strategy after the application of an effective glyphosate dose to control the resistant survivors is therefore absolutely necessary Targeting weed seed production after crop flowering Cutting for hay production, crop-topping and swathing are all late-season weed control techniques that are frequently used to target weed seed production. Hay crops can be specifically grown cereal crops, however, where high weed densities or drought are likely to reduce grain yield, crops may then be cut for hay production. In both situations the hay cutting has to occur prior to seed maturity in order to control annual ryegrass. Swathing of canola crops is routinely practiced as a harvest aid to reduce yield losses due to pre-harvest shedding. Depending on timing, swathing can also provide large reductions (>80%) in annual ryegrass seed production with the greatest benefits always resulting from the combination of swathing with narrow windrow burning. Crop-topping, the application of lower rates of the non-selective herbicides glyphosate and paraquat at crop maturity, is used to reduce annual weed seed production. For high levels of seed-set control, crop-topping must be done when weed seeds are still immature but the crop has fully developed. This allows these seed to be targeted without the risk of significant crop yield reductions. Crop-topping at later-than-optimum timing to avoid crop damage frequently results in annual ryegrass seed-set reductions of between 70 80%. However, crop-topping with glyphosate will not prevent seed production of glyphosate resistant weeds and the application with glyphosate for crop-topping selects for glyphosate resistance Targeting annual weed seed at harvest In Western Australia, high frequencies of herbicide resistant weed populations have constrained farming practices for the last decade, and now techniques targeting weed seeds during harvest are widely adopted and were driven by Western Australian farmers. The collection and management of the crop chaff containing large numbers of weed seeds can result in significant reductions in annual weed densities. This results in easier management of lower in-crop weed densities and the reduction of potential herbicide resistance. These systems effectively reduce the seed-bank of annual ryegrass, wild radish, and to a lesser extent wild oats and brome grass and their adoption has allowed continuous cropping systems to be practiced. 48

49 Chaff carts Chaff carts are towed behind headers during harvest with the aim of collecting the chaff fraction as it exits the harvester. The Australian Herbicide Resistance Initiative (AHRI) estimated the weed seed collection efficiency of several commercially operating harvesters with attached chaff carts with up to 85% of annual ryegrass and up to 95% of wild radish seeds that entered the front of the header during the harvest operation. The collected chaff must be managed to remove weed seeds from the cropping system and therefore this material is left in piles in the paddock to be burnt the following autumn. In some instances chaff is removed from the paddock and used as source of feed for livestock. Windrow burning The use of chutes attached to the rear of a harvester concentrates the straw and chaff residues into a narrow windrow during the harvest operation. This concentration of residue effectively increases the seed destruction potential of residue burning. With more fuel in the narrow windrows the residues burn hotter and longer than standing stubbles or conventional windrows. Results from a number of studies have found that up to 99% of both annual ryegrass and wild radish seeds can be killed by effective windrow burning treatments. Harrington Seed Destructor The Harrington Seed Destructor processes the chaff during the harvest operation to destroy weed seeds by dropping them through a series of bars rotating at high speed. This system removes the need to collect, handle and/or burn large volumes of chaff and straw residues, and returns the material to the paddock during harvest. Evaluation of this system under commercial harvest conditions by Australian Herbicide Resistance Initiative from 2008 to 2011 has determined that the Harrington Seed Destructor will destroy up to 95% of weed seeds that pass through it. Baling An alternative to the in-situ burning or grazing of chaff is to bale all chaff and straw material as it exits the harvester. The Bale Direct System developed by the Shields family in Wongan Hills, Western Australia, as a means for improving straw-hay production, consists of a large square baler directly attached to the harvester that collects and bales all harvest residues. A significant secondary benefit is the collection and removal of annual weed seed. Studies by AHRI determined that approximately 95% of annual ryegrass seed entering the harvester was collected in the bales. As well as an effective system for weed seed removal, the baled material can have a substantial economic value as a feed source. However, as with all baling systems, consideration must be given to nutrient removal from the paddock and sending seeds of resistant weeds to unsuspecting buyers. 49

50 7.5 Quarantine Preventing the movement of glyphosate resistant seeds onto the farm or between the paddocks is an essential element of glyphosate resistance management. Consistent and well-targeted monitoring for new infestations and controlling new outbreaks is pivotal to any quarantine strategy. Good quarantine procedures are also likely to minimise the introduction of new weed species or those that have resistance to other herbicide mode of actions. Weed introduction and spread can be reduced by good quarantine management at various critical points, including: Sowing of crop seed; Machinery and vehicle usage; Stock feed and livestock movement; and Fence lines and non-cropped areas in cropping paddocks such as irrigation channels. A well-managed on-farm quarantine plan will address each of these elements Contamination Point 1: Crop seed Purchasing certified or commercial seed is not a guarantee of weed-free status. Always check the fine print and the Seed Analysis Certificate. When purchasing seed of a public variety from another grower, be aware of possible weed seed contamination and where possible: Know the weed and resistance status of any farm from which you buy seed; Plan seed purchases ahead of time and inspect the paddock where the seed is being grown; Obtain a sample of the seed and have it analysed for both weed seed contamination and germination; and Contamination Point 2: Farm machinery and vehicles Implement a cleaning protocol for machinery and vehicles aimed at reducing new additions to the weed seed bank: Clean all farm machinery and vehicles before relocation; Pay special attention when moving from areas and/or paddocks with glyphosate resistant weed populations; and Make sure to enforce machinery cleaning standards with all harvest, baling, windrowing and grain transporting contractors. Glyphosate resistant patches should be managed separately to the entire paddock where possible, including during harvesting operations. Consider sacrificing the small area of crop infested with glyphosate resistant weeds. Alternatively, if weeds are more widespread, it may be possible to minimise the spread by using seed collection carts and modifying header trails or collecting seed in the grain sample for later removal. If possible, harvest paddocks in order from least weedy to most weedy, and finish clean areas in a paddock before harvesting more weedy areas. Take the time to clean bins, trucks and grain handling equipment (e.g. augers) between paddocks or seed-lots. This is an especially crucial step prior to harvesting and handling grain which will be retained for sowing subsequent crops. 50

51 Figure 19: Vehicle contamination with weed seeds (A. Storrie). Figure 20: Mud contamination of a vehicle (A. Storrie) Contamination Point 3: Livestock feeding and movement Grazing animals are likely to spread glyphosate resistant weeds within a farm, particularly in mixed cropping and grazing enterprises. New livestock, or those returning to the property from agistment, can also carry weed seeds from other areas. Contaminated fodder should be quarantined in a sacrifice paddock or feedlot, so that weeds are contained in a small area. Be aware of any contaminants that grain or hay may contain, and feed livestock in a way that ensures that contaminants are not spread. Drought feeding further exacerbates the issue as producers often drop their guard during stressful periods, and weeds are more difficult to control in dry conditions. 51

52 The same feeding precautions should be observed where chaff heaps collected at harvest from the header are grazed and/or baled for fodder or for feeding grain. Silage bears less risk for weed contamination because cutting is carried out when the weed seeds are less mature. More importantly, the silage process kills most weed seeds, although some do survive the ensiling process. Stock should be emptied out after feeding on weed seed contaminated fodder prior to returning to cropping paddocks. New stock should also be emptied out before moving onto clean country. If there is a designated feeding area, emptying will be easily achieved, and any weeds that grow in this area can be monitored, managed and contained. Livestock movement should be well planned to avoid the introduction or spread of new weeds around the farm. Remember that fleeces, hides and/or mud or dirt in hooves can also harbour and distribute weed seeds in addition to those relocated by faeces. Figure 21: Hay contaminated with weed seeds (A. Storrie) Contamination Point 4: Non-crop areas Weed infestations often flourish in non-crop areas (e.g. around buildings, along roadsides and fence lines) and the management of these populations will prevent weeds from spreading to other parts of the property. Glyphosate resistant weeds in non-crop areas can impact greatly on the farm weed status, but are often easily controlled. Weeds in non-crop areas have no crop competition and therefore able to produce large quantities of seed. Observant growers will have noticed that new weeds often tend to creep into the crop area from non-crop areas unless they are kept in check. Infestations along fence lines, paddock edges and non-crop areas of the crop paddocks can be controlled by herbicides, hay or silage cutting, and/or cultivation, or preferably a combination of all these options. As glyphosate is often used in these areas, the chances of promoting glyphosate resistant weeds are high. There are many alternative products that can be used to control glyphosate resistant weeds and the use of pre-emergence herbicides should be the first and is highly recommended. There are many effective long-term residual herbicides with various modes of action that can be applied. 52

53 Post-emergence options are generally fewer and need to be applied as an early post-emergence treatment. For example, many glyphosate resistant weeds such as fleabane, windmill, liverseed and awnless barnyard grass are difficult to control when fully matured. Researchers have found that excellent control is usually obtained prior to the early to mid-tillering stage for grasses and 5cm wide rosette stage for fleabane, especially when using Group L products (e.g. those containing paraquat or diquat). Figure 22: Fleabane contamination at the crop edge, Cecil Plains, Qld. (T. Cook) Other contamination points A commonly over-looked area of glyphosate resistant weed spread is the direct movement of seed by people, e.g. the introduction through clothing of farm workers. Windmill grass seed has small awns that enable it to attach to clothing, particularly socks. Similarly other grass seed without awns can adhere to damp footwear or accumulate in boots. Any glyphosate resistant seed could be transported in mud sticking to boots and be deposited anywhere once the clods of mud/soil detach. As glyphosate resistance is an international issue, be careful not to contaminate clothing when visiting overseas farming regions. Other vectors of glyphosate resistant weed spread include: Waterways are subject to occasional flooding, spreading weeds from property to property or between paddocks; Wind dispersed seeds such as fleabane and windmill grass could be transported over great distances by strong winds or whirlwinds; Native or feral animals could spread the occasional seed; and Easements on properties with high traffic movement are subject to weed spread. 53

54 8. Case Study 8.1 Management of glyphosate resistant annual ryegrass in a mixed farm in Western Australia 8.2 Introduction On a mixed enterprise farm near Northam, WA, glyphosate resistant annual ryegrass developed in a vineyard in 2004 caused by the repeated application of glyphosate. By 2007, glyphosate resistant ryegrass started to spread from the vineyard to the surrounding ryegrass-based pasture fields. The grower devised a management strategy to prevent the spread of glyphosate resistance throughout the remainder of the property. The Department of Agriculture and Food WA (DAFWA) monitored resistance spread from 2007 to Management of resistant ryegrass was complicated by an outbreak of annual ryegrass toxicity (ARGT), which killed several cattle. By 2010 the management strategy had resulted in the elimination of ARGT and substantially reduced the frequency of glyphosate resistant ryegrass on the property. 8.3 Property characteristics The 31 ha farm in Northam, Western Australia, was acquired by the current owner in The property consists of a vineyard (1.2 ha), citrus orchard (1 ha) and surrounding fields that are cropped (oaten-hay production) or used for subterranean clover and annual ryegrass-based pasture grazed by cattle or sheep. Herbicides are applied annually between the rows of vines in the vineyard, to fire breaks and along fence lines. In most years, no herbicide is applied to cropping and pasture paddocks. The property is bordered by native vegetation on all sides and a river is its western boundary. Summary Location: Shire of Northam, central wheatbelt, Western Australia Rainfall: winter dominant, 450mm average annual rainfall Soil type: mainly brown clay loam, with increased elevation high percentage of gravel and rocks (e.g. in the fields above the river flood plain) Enterprises: vineyard, citrus orchard, cattle and sheep, cropping for winter hay Major weed problems: annual ryegrass Herbicide resistance status: annual ryegrass resistant to glyphosate Results of the management program: prevention of the spread of glyphosate resistance and direct economic gains through management of annual ryegrass toxicity 54

55 55 Figure 23: Aerial photograph of the property (blue property border) which consists of a vineyard with a citrus orchard to the east and pasture/cropping field to the north, west and south. The house/sheds are the white shapes to the south-east of the vineyard. The property is bordered by native vegetation (dark green areas), with a river along the western boundary.

56 Figure 24: Glyphosate resistant annual ryegrass along the vine row (A. Storrie). Problems and History Herbicide resistance: Since 1991 glyphosate had been applied between the rows of vines, within the vineyard annually. Grapes in the vineyard are harvested by hand, and the aim of weed control in the vineyard was to kill or suppress the growth of ryegrass to improve grape production and to ensure access to the vines during harvest. Control of ryegrass failed in 2002, 2003 and In 2004 seeds from surviving plants were collected by DAFWA and subsequent resistance testing indicated that 79% of plants were resistant to glyphosate. Annual ryegrass toxicity (ARGT): ARGT is common in dense populations of ryegrass. It is caused by the invasion the mature seed head of ryegrass by a coryneform bacteria, which then causes the formation of the poisonous corynetoxin. Once the mature seed heads dry, any livestock that eat the poisonous seed heads may die. ARGT was diagnosed on the property in 2008, following the death of several cattle. 56

57 8.4 Management program Aims of the program The grower aimed to minimise the spread of glyphosate resistant ryegrass though the remainder of his property and to reduce the probability that resistance would spread to neighbouring farms. A second aim was to eliminate the ARGT. However, the grower desired to maintain a profitable business and did not want to eradicate ryegrass as it was the basis of the pasture forage. The chance of spreading glyphosate resistant ryegrass to neighbouring properties was minimal. Transfer of seed was prevented by avoiding vehicle, stock and hay movement between properties, e.g. by practicing good farm hygiene techniques. Additionally, the native vegetation that surrounded the property represented a buffer zone around the property as there was no ryegrass growing in those areas. This reduced the likelihood that annual ryegrass pollen would be able to move to a neighbouring property. Management practices: A management plan was developed in consultation with neighbours, local agronomists and the DAFWA. The grower did not want to develop a high input enterprise, and a personal preference for minimal herbicide use was incorporated into the management plan. Glyphosate use continued in the vineyard even after the annual ryegrass became resistant as it was the safest and most cost effective herbicide for weed control. Spray.Seed was also used. In 2007, the paddocks around the vineyard were grazed throughout the year. In 2008, all surrounding fields that were used for both hay and pasture included a spray-topping application to the hay and pasture with 400 ml/ha paraquat (250 g a.i./l) immediately after ryegrass head emergence to prevent the formation of mature seed heads. However, while effective, this management strategy went against the grower s desire to minimise herbicide use. In 2009, biological control of ARGT was implemented. The grower firstly sowed 8 kg/ha of Safeguard ryegrass, which is resistant to ARGT. He then spread twist fungus (at 200 g/ha), which competes with the coryneform bacteria and prevents the development of toxin in mature ryegrass heads. Twist fungus was ideal for this property, as it prefers wetter seasons and regions. Once established, the twist fungus population along the water way on the western boundary acts as a reservoir of inoculum following dry seasons. In 2009 and 2010, the area was grazed, except for the fields next to the vineyard which were not grazed at ryegrass flowering. The property was monitored for glyphosate resistant ryegrass from 2007 to Manipulation of the number of herbicide susceptible annual ryegrass plants to minimise resistance spread There are two choices to reduce resistance spread. The first is to greatly reduce the number of annual ryegrass plants. The second is to greatly increase the number of susceptible plants, so that susceptible pollen competes more effectively with resistant pollen. The farmer wished to maintain annual ryegrass on the property as a forage species and to reduce the use of herbicides. Therefore the grower aimed to maintain a high population of annual ryegrass in the fields around the vineyard. 57

58 Other considerations In 2008, in order to avoid stock losses from ARGT the high density of susceptible plants had to be reduced. Safeguard ryegrass was used to increase the density of ryegrass in the following year; it is susceptible to glyphosate (and resistant to ARGT). To increase pollen production from the susceptible ryegrass to compete with the resistant pollen, it was necessary to avoid grazing the paddocks closest to the vineyard at flowering time. This new grazing program required more planning than a regime of continuous grazing, but it was possible to keep stock in the northern and southern fields during ryegrass flowering, without resorting to supplementary feeding. Results 2007: In 2007, heavy grazing of ryegrass before and during flowering reduced the pollen production of susceptible ryegrass plants within the pasture, but the glyphosate resistant ryegrass plants in the vineyard were not prevented from flowering. This provided a higher probability of susceptible plants being pollinated with resistant pollen from the vineyard. Nine glyphosate resistant plants were found on the property in 2007, with five of these plants located outside the vineyard. 2008: The practice of spray-topping in the paddocks surrounding the vineyard dramatically reduced the number of ryegrass that produced mature seed heads. This prevented further stock deaths from ARGT. However, the number of susceptible ryegrass plants that survived the spray-topping operation was low. Again, most of the pollen was produced by the resistant plants in the vineyard, and there was a very high chance of resistant plants pollinating susceptible plants. Fifty-four glyphosate resistant annual ryegrass plants were found throughout the farm in : Sowing Safeguard ryegrass and spreading the twist fungus were successful in managing ARGT and no stock died. Sowing Safeguard ryegrass also increased the density of glyphosate-susceptible plants on the farm and their pollen production was maximised by lenient grazing at flowering. Only six glyphosate resistant ryegrass plants were found on the property in late This reduction since 2008 could be due to a minor weakness glyphosate resistant ryegrass carries, allowing susceptible plants to compete if glyphosate is not used. 58

59 59 Figure 25: Aerial photographs from 2007 to The red dots indicate the presence of glyphosate resistant annual ryegrass in the vineyard or surrounding crop/pasture fields.

60 2010: The strategy of 2009 was continued. A dense population of ryegrass was maintained and was not grazed at flowering. Spray.Seed was used to control ryegrass in the vineyard. Three glyphosate resistant ryegrass plants were found in late 2010, only one of which was outside the vineyard. 8.5 Conclusions The strategy of maintaining a high density of glyphosate-susceptible annual ryegrass was successful in limiting the spread of glyphosate resistance on this property. The management strategy was in line with the grower s desire to minimise herbicide use and was cheap to implement. This strategy did not require a change to the normal enterprises carried out on the farm and did not substantially reduce productivity. 60

61 9. Case Study 9.1 Management of glyphosate resistant awnless barnyard grass and annual ryegrass in northern NSW 9.2 Introduction There are two species of weeds resistant to glyphosate on this farm at Bellata in northern NSW. The first and most widespread species is awnless barnyard grass and resistance was first suspected in the summer of 2004/05 and later confirmed in 2007/08. The second species exhibiting resistance to glyphosate is annual ryegrass and was suspected of being resistant in 2010 and confirmed in The extent of the annual ryegrass infestation is limited to a patch less than a hectare. Since the confirmation of resistance to glyphosate, the barnyard grass population has been in steady decline due to improved management practices. Weed management on this property is flexible, using chemical and non-chemical options. However, there have been some challenges, such as a wet summer period in 2009/10 reducing the persistence and effectiveness of preemergent herbicides. Rapid growth of barnyard grass combined with wet summers resulted in barnyard grass management tactics aimed at large plants, thus limiting the effectiveness of many post-emergence options. Knowledge gaps on how to optimise the use of bipyridyl herbicides also caused some difficulties. The recent addition of glyphosate resistant annual ryegrass further increased the complexity of the overall weed management on this farm. 9.3 Property characteristics The 840ha farm near Bellata, north of Narrabri, New South Wales was acquired by the current owner in 1993 and been under his sole management since. An occasionally flowing watercourse passes through the farm and could be a vector for dispersal of glyphosate resistant weed seed after heavy rainfall. The property is lightly stocked with cattle which infrequently has been used for grazing weeds and failed crops. Cattle could spread resistant weed seeds. The soil types on the property vary and this contributes to the inconsistent control results and increases persistence of resistant awnless barnyard grass in dry seasons. Summary Location: Narrabri Shire, northern grain belt, New South Wales; Rainfall: summer dominant, 600 mm average annual rainfall; Soil type: variable, from black vertisol to sandy clay loam; Enterprises: predominantly winter cereals and the occasional faba bean crop; Summer crops are sunflowers, sorghum and mung beans. There are some cattle on the property which occasionally graze on cropping paddocks during the fallow; Major weed problems: awnless barnyard grass, Johnson grass (Sorghum halepense), wild oats (Avena spp.) and annual ryegrass; Herbicide resistance status: glyphosate resistant barnyard grass and glyphosate 61

62 resistant annual ryegrass and; Results of the management program: Glyphosate resistant barnyard grass populations have been reduced to a very sparse (10 plants per ha) but widespread infestations of over 10% of the property area, compared to approximately 1000 plants per m 2 in 2006/07. The farm profitability has been reduced slightly as some of the tactics used have a moderate increase in cost compared to management without glyphosate resistance. Glyphosate resistant annual ryegrass since 2012 was managed by spot treatment with a selective grass herbicide (Group A) combined with hand weeding of the survivors. Figure 26: Sandy loam soil in dry times leading to failed sorghum crops while allowing the survival and seeding of glyphosate resistant barnyard grass (Tony Cook). Figure 27: The density of barnyard grass immediately after confirmation of glyphosate resistance in 2007 was approximately 1,000 plants/m 2 (Tony Cook). 62

63 Problems and History In 2004/05 the farmer realised a patch of barnyard grass was becoming difficult to control, however resistance testing was not undertaken until 2006/07, leading to a few years of poor control. Results confirmed a moderate 7-fold resistance to glyphosate. The farmer believes that resistance developed through repeated applications of glyphosate in his zero-till system and poor control of a high numbers of weeds. In this area a low number of glyphosate resistant plants were able to survive in patches and spread from there. However, the infestation of glyphosate resistant barnyard grass is still limited to less than 10% of the farm with only two paddocks infested. Other resistance problems on this farm include the recent development of glyphosate resistant annual ryegrass along a contour bank that had been repeatedly treated with glyphosate. As this area is very small, the infestation will be patch managed and impact on the overall farm operations is unlikely. It is suspected that populations of wild oats resistant to Group A herbicides exist in several paddocks and they appear to be at the early stages of spread. A thorough resistance test is yet to be conducted. 9.4 Management program The approximate size of the awnless barnyard grass infestation is about 80 hectares. Although the owner considers this infestation is only present in two paddocks, it may have spread to other parts of the property. The grower intends to regularly monitor other paddocks and to control any suspect patches which will prevent new large scale infestations. Weed management plans have been developed with a private agronomist and a state government weed expert. Information was gathered from GRDC grower updates, field days, herbicide resistance newsletters and having trials located on the property. This improved the farmer s level of understanding of the weeds ecology, and highlighted alternative methods of control that could be used in developing a weed management plan. The grower claimed there were no limitations or barriers to adopting new weed management tactics which included different herbicide mode-of-actions, cultivation to control large plants and using the double knock technique. Integrated awnless barnyard grass strategies used since glyphosate resistance was confirmed included: Removing sorghum and sunflower from the rotation in affected paddocks as these crops increase barnyard grass densities. Most of the control tactics are now employed in the fallow phase. Using Flame (Group B) and atrazine (Group C) as a pre-emergent fallow treatment in early spring. This tank mix was the superior pre-emergence treatment confirmed in research trials and farmer demonstrations. Regularly monitoring of affected paddocks and hand weeding light infestations of barnyard grass. This occurred after barnyard grass populations were reduced to extremely low levels. Cultivation to control large barnyard grass of sizes greater than mid tillering stage. There are no registered chemical options to control barnyard grass beyond the early tillering stage, except glyphosate (Figure 29). Application of the double knock technique in fallow: either using a Group A herbicide or Flame (Group B) followed with a Group L herbicide. 63

64 Results Initial infestations were very dense and were estimated to be over 1,000 plants/m 2 in some patches (refer to Figure 27). After four years of active management, the density of barnyard grass is approximately 10 plants per ha. Although the farmer now uses a hand weeding strategy to control survivors, reliance on effective pre-emergence herbicides remains a critical part to glyphosate resistant barnyard grass management. A wet period in the 2008/09 season tested the determination of the grower. The initial application of a pre-emergence herbicide did not effectively control the first few flushes of barnyard grass and extended periods of wet weather prevented the farmer from treating the seedlings. Sequential applications of paraquat were required to prevent large barnyard grass plants from setting seed. Although this fallow management was expensive, it was limited to a small proportion of the farm and resulted in cleaner fallows the following year. The farmer believes he may eradicate the problem in a few more years. Whether eradication is possible or not, the grower has increased his awareness of glyphosate resistant weeds, using non-glyphosate-based strategies and understands that without seed production, weeds cannot perpetuate resistance. Challenges No challenges arose after glyphosate resistance was confirmed, because the farmer had no mind-set limitations to what had to be done. There was no hesitation using cultivation or Group L herbicides. Often farmers refuse to cultivate due to potential damage to soil structure or soil moisture loss and the use of Group L herbicides can be perceived as too hazardous for the applicator. However, planning, good timing and the use of appropriate safeguards enable these tactics to be integrated into the farming system. Although the original infestation was confined to a small part of the farm only, resistance could have spread to other areas. Therefore, the farmer monitored surrounding areas and likely corridors of spread, such as verges of farm roads to manage this risk. Costs of the control of glyphosate resistant barnyard grass in affected paddocks increased significantly and were dependent on treatment success. In the wet season of 2008/09, costs were estimated to be approximately $80/ha higher than prior to developing glyphosate resistance. Until today, even when treatments - including residual herbicides - are working well, costs have been $30 to $40 higher than the expenditure for the regular practice of the repeated spraying with glyphosate. However, the farmer sees this additional expenditure as an investment to allow him to continue farming. Without this investment barnyard grass populations would increase in density and spread across the farm, threatening moisture conservation in fallows and reducing yields in subsequent crops. 64

65 Figure 28: Although there are effective pre-emergence herbicides for use in sorghum, only a few survivors are capable of producing large numbers of seed and re-setting the seedbank. This plant has survived an inter-row treatment aimed at controlling survivors (Tony Cook) Figure 29: Cultivation was effective at controlling large glyphosate resistant barn-yard grass (Tony Cook). 65

66 Annual ryegrass As outlined before, the farm has the unenviable situation of having two weed species resistant to glyphosate. However, resistance to glyphosate in annual ryegrass is still confined to a small area of approximately 1 ha along a contour bank with a smaller number of plants scattered into the cropping area (refer to Figure 30). The infestation should be easily controlled. The farmer has just commenced a weed management plan for annual ryegrass with the first tactic to treat all plants with an effective Group A herbicide. Any survivors will then be hand weeded. Regular monitoring of all paddocks of the farm, in particular surrounding areas to the infestation, is planned to determine whether this patch has spread to other parts of the farm. Wild oats potentially resistant to Group A herbicides There are also concerns that wild oats have developed resistance to Group A herbicides, though at the time of writing no herbicide test has been conducted on the suspect population. The farmer has noticed classic resistance signs of weed patches developing. There were small clumps of advanced healthy plants surrounded by dead wild oats with no other plausible explanation of survival, except for resistance. It has been strongly recommended for a resistance test to be conducted as soon as possible. It has to be noted that these wild oat plants are more widespread and occur in more paddocks, including those with glyphosate resistant barnyard grass. If Group A resistance is confirmed, it would have serious implications to the overall weed management on this property, because the farmer has included more winter cropping in the rotation. This included the use of summer fallow management to control glyphosate resistant barnyard grass populations increasing the pressure on wild oat herbicides used in-crops. Figure 30: A new threat of glyphosate resistant annual ryegrass on a contour bank (Tony Cook).

67 9.5 Conclusions Glyphosate resistance management is a daunting task for farmers with newly confirmed infestations and difficult if multiple species are resistant to glyphosate. In this case study a grain grower experienced this problem, however positive outcomes from this property are: The grower is now aware of the problems of resistance and is being proactive in his weed management; The new patch of glyphosate resistant annual ryegrass is very small and control should be easy; Both glyphosate resistant barnyard grass and annual ryegrass occur on separate paddocks and their management does not impact on each other; The initial high densities of glyphosate resistant barnyard grass have been significantly reduced to the occurrence of scattered plants only; and Weed management strategies have maintained consistent pressure on weed numbers and there is the potential to eradicate both glyphosate resistance problems. Key learning outcomes from this case study are: Weed management must be a high priority; Thorough monitoring of the applied weed control including the treatment of any survivors is important to never allow the weeds to set seed; Residual herbicides will lessen pressure of post-emergent herbicides; High levels of weed control should be implemented early to minimise longer term impacts of glyphosate resistant weeds; Control tactics should be varied and non-herbicide treatments are essential, e.g. strategic cultivation; Patch management of weeds, flexibility and the maintenance of efforts to all aspects of the management is absolutely necessary; Resistance testing will be beneficial to determine control tactics; and. Keep an open mind and embrace change. 67

68 10. Case Study 10.1 Management of glyphosate resistant liverseed grass in northern NSW 10.2 Introduction A Pallamallawa farmer and his agronomist noticed a suspect patch of liverseed grass in the summer of 2007/08. Plants were immediately sent for resistance testing using the Quick test and resistance to glyphosate was confirmed. Since being confirmed as resistant to glyphosate, the farmer has been unrelenting in his efforts to control the small patch (<1 ha) of liverseed grass. The farmer and his father had been managing the property for 13 years and the previous owner, a cattleman, did not consider weed control as a high priority. This suggests that the glyphosate resistance developed after 13 years of intensive selection pressure Property characteristics A 600ha farm, located at Pallamallawa, east of Moree, in New South Wales was acquired by the current owner in Approximately 10 paddocks are used in a barley chickpea wheat - long fallow - summer crop rotation. Three centre pivot irrigators are used for high value crop production. Summary Location: Moree Plains Shire, northern grain belt, New South Wales Rainfall: summer dominant, 620mm average annual rainfall Soil type: red clay loam Enterprises: predominantly winter cereals and chickpeas with a third of the property sown to cotton and sorghum Major weed problems: liverseed grass, wild oats, wild radish in small patches Herbicide resistance status: liverseed grass resistant to glyphosate Results of management program: early detection of the problem and continuous control of survivors using alternative tactics, patch management of the infestation with regular monitoring, the farm is profitable with minimal additional control costs while the affected area remains small Problems and History 68 A suspect patch was first identified by the farmer s agronomist in January Live plants were promptly sent for resistance testing and the results confirmed a moderate 7-fold resistance to glyphosate. The farmer believes resistance had evolved from the heavy reliance on glyphosate and ineffective levels of control achieved with cultivation (not full disturbance). Prior to the purchase in 1998, the previous owner managed the land for cattle production and grass weed management was not a high priority. Both liverseed grass and barnyard grass were seen as good stock feed. This meant that these weeds were at high densities when the current owner purchased the property.

69 69 Figure 31: Property plan showing the small area affected by glyphosate resistant liverseed grass (Tony Cook).

70 10.4 Management program Since the original size of the infestation was very small (approximately 1 ha), the grower s intention was to reduce the infestation dramatically in size to achieve full eradication. As the infestation covered only a small proportion of the paddock, management strategies were targeted to that patch and not applied to the whole paddock. The farmer s agronomist recommended changing herbicide mode of actions, increasing the frequency and effectiveness of cultivation and using the double knock technique. Occasionally the farmer still used glyphosate at maximum label rate, particularly as the first knock in the double knock. Figure 32: The area in the foreground was infested with glyphosate resistant liverseed grass and is now cropped with winter cereal for brown manuring. The biomass from this crop will not be disturbed by cultivation and provide a good mulch to reduce germination of liverseed grass from October to December. Centre pivot irrigator the in background. (Tony Cook) The newly adopted methods for the control for liverseed grass are: Flame (Group B) as a fallow pre-emergence treatment early in the summer fallow; Double knock 1 - Applying a Group A herbicide followed by a bipyridyl herbicide (Group L) 5-7 days after the Group A herbicide; Double knock 2 - applying maximum label rates of glyphosate followed by a bipyridyl herbicide (Group L); Double cultivation with wide sweep points to ensure full disturbance, followed by monitoring to ensure 100% kill; and Brown manuring winter cereals using the decaying biomass as a mulch to reduce liverseed grass establishment. 70