MANAGING GLYPHOSATE RESISTANT ANNUAL RYEGRASS IN A MIXED FARM IN WESTERN AUSTRALIA CASE STUDY

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1 MANAGING GLYPHOSATE RESISTANT ANNUAL RYEGRASS IN A MIXED FARM IN WESTERN AUSTRALIA CASE STUDY Catherine Borger Abul Hashem March 2013 funded by In partnership with

2 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 31ha 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

3 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.

4 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. 6 6 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.

5 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.

6 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.

7 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.

8 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. For more information on this case study contact Catherine Borger, Department of Agriculture and Food Western Australia: Phone: (08) catherine.borger@agric.wa.gov.au