In Search of Effective Herbicides for Chickpeas.

Transcription

1 In Search of Effective Herbicides for Chickpeas. F.A. Holm 1, K. Sapsford 1, E. N. Johnson 2, R. McVicar 3 and K. Kirkland 4. 1 Crop Development Centre, University of Saskatchewan, Saskatoon, SK, 2 Agriculture and Agri-Food Canada, Scott, SK., 3 Saskatchewan Agriculture and Food, Regina, SK. 4 Kirkland Crop Tech, Vermilion, AB Introduction: In general, chickpeas are poor competitors with weeds and are more sensitive to many herbicides than other pulse crops such as field peas and lentils. This is especially true in the case of post-emergence herbicides for the control of broadleaved weeds. Therefore, herbicide choices for broadleaved weed control are limited and hard to control broadleaved species can cause significant problems for chickpea producers. To date, relatively few herbicides have been registered on this crop. The responses to the following 13 questions provide a summary of our experience to date with the use of herbicides on this crop. Question 1. Are any pre-emergence herbicides safe to use on chickpeas? Chickpeas have good tolerance to both trifluralin (Treflan, Rival, several other trade names) and to ethalfluralin (Edge ). In extensive testing of pre-plant incorporated applications at Saskatoon and other locations in Saskatchewan, Edge has been safe to use on the crop. In some cases, very slight effects on the crop have been noted from spring applications but this has not affected time to maturity or seed yield. No crop injury has been noted when Edge was applied in the fall. Desi and Kabuli types appear to be equally tolerant to these herbicides. Question 2. Are any of these products registered for use on chickpeas? No. New use patterns for these herbicides have not been approved in Canada for a considerable length of time. We do not know if or when Edge will be registered for use on this crop. Question 3. Could I use Avadex or Fortress on chickpeas? To our knowledge, these products have not been tested on chickpeas. Based on their mode of actions and their use patterns in other crops, we would not expect them to injure chickpeas. However, they are not registered and, therefore, should not be used.

2 Question 4. What about post-emergence products for annual grass control? Chickpeas have excellent tolerance to Group 1 herbicides. Both Poast and Select are registered for use on both types of chickpeas. Rates are the same as for other crops and applications should be timed for optimum grass control as crop safety is not affected by crop stage. Question 5. What about post-emergence herbicides for broadleaved weeds? Sencor is the only post-emergence product that is registered for control of broadleaved weeds in chickpeas. Both types of chickpea are considerably more sensitive to this herbicide than are lentils. Early application is critical in order to minimize crop injury. Apply the herbicide any time from ground crack (crop just starting to emerge) until the plants are about 6 cm (2.5 inches) tall (plants have 1 3 above ground nodes). Delaying application past this stage will result in excessive leaf burning that can delay maturity and, in some cases, reduce yield. Application of Sencor to 15 cm (6 inch) tall chickpeas has reduced yield by up to 40% in our trials. Sencor is not registered for use on soils with less than 4 % organic matter and chickpeas should be seeded at least 5 cm (2 inches) deep. Early application is also necessary in order to achieve acceptable weed control. Delaying application in order to control late emerging weeds is not recommended as the earliest emerging weeds compete most strongly with the crop and will be the most difficult to control if treatment is delayed. Weeds should be no more than 5 cm (2 inches) in height or diameter. In chickpeas, Sencor is registered for suppression of: ball mustard, chickweed, corn spurry, green smartweed, hemp-nettle, lamb s quarters, stinkweed, tartary buckwheat, volunteer canola and wild mustard. Question 6. Can I mix Sencor with a post-emergence herbicide for annual grass control? These tank-mixes are not registered and are not recommended as the optimum timing of the two products does not coincide and a tank-mix of the two will result in significantly more crop damage than will result from Sencor applied alone. Apply the Sencor first and then apply the grass killer after the crop shows significant recovery from any Sencor injury. Question 7. Products like MCPA, Tropotox Plus Pea Pack and Basagran can all be used to control broadleaved weeds in field peas. Can I also use them on chickpeas? No. All of these products cause serious injury to chickpeas, even at relatively low rates.

3 Question 8. Is it safe to apply Odyssey or Pursuit post-emergence to chickpeas? No. In our trials, post-emergence applications of these products, even at reduced rates, have resulted in severe injury to chickpeas that has delayed maturity and, in some cases, reduced yield. Question 9. Are there any other potential post-emergence options for broadleaved weeds? There are two other products that show promise but the prospects of them ever being registered in Canada seem remote. Pyridate (Lentagran in Canada, Tough in the USA) is very safe on the crop and controls a fairly wide spectrum of broadleaved weeds including Russian thistle and kochia. In other countries it is used on crops such as peanuts, cole crops, oilseed rape, asparagus, alfalfa, red clover, and chickpeas. Application rates twice that needed for acceptable weed control have not caused crop injury in our trials and the product does not leave any soil residues that will interfere with rotational crops. The crop appears to be tolerant at all stages of application. Sulfentrazone (Authority ) is a pre-emergence or pre-plant incorporated product for control of annual grasses and broadleaved weeds that has shown promise in more limited testing. It is used on soybean in the USA and is being developed for use on sunflower. Crop tolerance was good in preliminary trials in 2000 but its weed spectrum has not yet been well defined. A major concern is that this product persists in the soil. In the USA, cereals, alfalfa, and dry beans can be grown the year following application but there is an 18 month recropping interval for flax, lentil and mustard and a 30 month re-cropping interval for canola and potatoes. We are conducting re-crop trials this summer to identify potential re-crop problems. Question 10. I ve heard that some growers apply a light rate of imazethapyr (Pursuit ) along with the glyphosate burn-off prior to emergence of chickpeas. What has the research experience been? Yes, some growers are using an unregistered tank-mix of glyphosate + 25% - 50% of the recommended rate of Pursuit for their direct-seeding burn-off treatment. This treatment has shown mixed results in research trials. When light rain falls shortly after (within a few days) application, residual weed control from the Pursuit has often been quite good. However, if no rain falls for an extended period after spraying, weeds can emerge through the herbicide. At 25% of the recommended rate, weed control has not been satisfactory in the majority of cases in our trials. Growers should be reminded that Pursuit is not registered for use on chickpeas and not on any other crop in the area where chickpeas are grown.

4 Some crop injury has been noted with this treatment and this has often been temporary but growth of the crop can be slowed down or even stopped for a period of time and this can result in delayed maturity. The greatest amount of crop damage has been noted when heavy rain has fallen shortly after application. It is believed that this results in the herbicide leaching into the root zone of the young crop plants, thus increasing the amount of herbicide taken up by the crop. Tolerant legume crops are not injured by these herbicides because they can metabolize the herbicide, thus breaking it down into harmless compounds. Some legumes such as peas and alfalfa apparently can break down the herbicide more quickly than other, more sensitive, species such as lentils and chickpeas. Therefore, the degree of damage suffered by these more sensitive crops is very likely influenced by the rate of uptake of the herbicide into the plants and the rate of breakdown of the herbicide in the plant, both of which will be affected by soil moisture and air temperature. Conditions that result in slow plant growth (therefore low rates of metabolism) may result in increased crop injury and a prolonged recovery period and yield loss. Question11. Are there any residue carry-over concerns when using Pursuit at these reduced rates? It depends. In re-crop trials on a heavy clay soil with % organic matter and a soil ph of 7.8, cereals and canola have not been injured the year following treatment. However, on lighter textured soils with lower organic matter and/or low ph (below 7.0), these crops can be injured when they are grown the following year. We would expect canola (except Clearfield canola) to be severely injured and we would not recommend seeding oats the following year. Barley, durum and spring wheat could also be affected. Reduced tillering, delayed maturity and reduced yield can be expected on lighter textured soils, especially those with lower organic matter levels and/or a ph below 7.0. Barley and durum appear to be more sensitive to Pursuit residues in soil than does spring wheat. Application of 1/3 the recommended rate of Pursuit is approximately equal to application of the recommended rate of Odyssey in terms of soil residual potential. The degree of risk to susceptible rotational crops cannot be accurately predicted because it is the result of a combination of herbicide application rate, soil texture, soil organic matter, soil ph and the soil moisture content throughout the year of application and the subsequent year. Breakdown of the herbicide in soil is most rapid when the soil is moist, therefore, residue carry-over will be greater following a dry growing season. Lowest risk would be with a combination of fine textured soil, relatively high organic matter, ph above 7.0 and good moisture throughout the growing season and into the next year. Conversely, a sandy soil, low organic matter, ph less than 7.0 and dry weather would be high risk for susceptible crops grown in the rotation. Notwithstanding all of the above, we would expect that a dry growing season following application of a 1/3 recommended rate of Pursuit will likely result in herbicide carry-over levels that will damage cereals or canola planted in the following year. It should be remembered that is not registered for use in the brown and dark brown soil zones.

5 Question 12. What can I use to control perennial broadleaved weeds like Canada thistle and sow-thistle in chickpeas? Nothing. There are no selective herbicides that will control these weeds in this crop. If perennial weeds are a problem in fields intended for chickpeas, they should be controlled in other years of the rotation. Products containing clopyralid (Lontrel based products) should not be used because of soil residue concerns. Thus, the only practical alternative is a glyphosate treatment. Pre-harvest is the preferred timing. Question 13. Can I use Reglone Pro to desiccate chickpeas? Data to support the registration of Reglone Pro for desiccation of chickpeas has been submitted and it is expected that this use will be approved in time for the 2001 harvest season. Chickpea is a long season crop so it is important to remember that use of a desiccant does not speed up the maturity of the crop. The seed MUST be mature before the desiccant is applied. Desiccants merely speed the dry-down of the vegetation and can reduce the time from seed maturity to harvest. In general, in our trials, treatment with has had minimal effect on the rate of dry-down on the pod material of the Kabuli type. It was much more effective on the Desi type. The proposed timing statement is as follows: Apply REGLONE at the time swathing would normally commence. This is when the majority of plants are yellow and most pods are mature and seeds have turned from green to yellow or brown. Upper part of plant may still be green. Growers should not use this treatment unless and until it becomes a registered treatment. Acknowledgements: The authors acknowledge the technical assistance of Mr. Gerry Stuber and Ms. Teri Ife, Crop Development Centre, University of Saskatchewan, Mr. Herb Schnell, Agriculture and Agri-Food Canada, Scott, SK, personnel at various Spoke Sites throughout Saskatchewan and the financial support of the Agri-Food Innovation Fund.