Applying residual herbicides in oilseed rape – the latest advice

UK - November 22, 2011

Normally by now growers would be applying their Kerb Flo in oilseed rape, but this season is proving to be different and weed control experts are advising growers how best to tackle the issue.

In areas where black-grass is a problem, growers need to optimise performance of any herbicide and to implement a sound weed resistance management strategy.  Dr. Stephen Moss of Rothamsted Research is concerned that grass weed resistance could be lower on growers’ agenda this year. “Last year we enjoyed what I describe as a ‘quadruple whammy’ of weed control - good seedbeds and establishment, really good pre-em performance, a cold winter and a dry spring. It couldn’t have been better for weed control, but this year is already proving to be completely different and growers can not afford to be complacent.”

“Grass-weed resistance is still a major issue for many arable farmers and we need to use a range of control methods to lower the weed burden and minimise weed resistance pressure. Crops such as oilseed rape and beans have an important role to play in breaking the cycle and managing weed resistance, as different chemistry can be used in these crops. Active ingredients such as propyzamide have a vital role to play, as there is no evidence of weed resistance to this active ingredient at all and its use can result in good levels of grass-weed control. But growers need to focus on getting the best performance they can this autumn.”

Andy Bailey of Dow AgroSciences agrees that oilseed rape still plays a crucial role as a cleaning crop.  “We can use different chemistry in broad-leaved crops than we can in cereals, but weed control still needs to be spot-on in these crops. Kerb Flo gives very good levels of control of black-grass and rye-grass, but conditions of application need to be right.”

Andy explains that for optimal performance of Kerb Flo, you need sufficient soil moisture and cool soil temperatures – around 10°C is ideal.  “When it is cold, the residual life is much longer and the end-effect much better. In most seasons, these conditions are reached from November onwards, but this has not been the case this autumn. This year applications have moved to the end of November or into December and January.”

“But for black-grass control it’s worth waiting, so that the best results can be achieved. Certainly the weather is getting colder and I would expect conditions to be ‘good to go’ imminently.”

Andy Bailey advises that where Kerb Flo is being applied for annual meadow-grass and broad-leaved weed control, applications may be made straight away. “For optimal performance for black-grass and rye-grass from Kerb Flo, Dow AgroSciences recommend applications are made when soil temperatures have got down to 10°C and falling and soil moisture deficit at 30cms is no more than 50 mm and falling. The time for Kerb Flo application in the North is here and in other parts of the country it is getting close. Where crop canopies are advanced, if you can treatments should be delayed until winter die-back or pigeon grazing allows applications to reach the soil surface,” says Andy.

However he understands that this may not a realistic option on heavy soils.  “Where Kerb is applied to leaves, product degradation is unlikely as degradation is by microbial action in the soil. With sufficient rain, any Kerb Flo that has dried on the leaf will dissolve and drop-down occurs onto the soil surface. The resulting ‘spread’ across the soil surface may not be directly comparable to applications made to more open crops,” explains Andy.

“I would also advise using the full label dose rate of 2.1 l/ha for Kerb Flo. When you have an opportunity to hit weeds hard, you should do so. Kerb Flo controls all black-grass, irrespective of resistance status. Propyzamide is from a distinct group of chemicals, the benzamides. It has no known resistance problems of black-grass, rye-grass or wild-oats, weeds that have increasingly widespread de-sensitisation to other groups of chemistry. Providing you get conditions right for performance, it plays a key role in tackling susceptible and resistant grass-weeds across the rotation,” he says.

Researcher Stephen Moss advises adding in a contact graminicide for extra reliability on black-grass. “Even if there is resistance to the fop or dim, it seems to add to the activity. Growers need to understand the resistance profile on their own farm in order to choose the best partner graminicide. Use your own local experience and farm knowledge to gauge this.”

Andy Bailey urges growers to support the Stewardship campaign for propyzamide. “It is imperative that growers adhere strictly to guidelines in order to avoid any risk of water pollution. A strong Stewardship campaign not only advises how best to do this but also invests in further research to look for further positive advice. It also helps advisors by communicating such findings and seasonal factors to aid best results.”

He adds that the investment Dow AgroSciences has made in developing and refining advice on Kerb Flo means that this herbicide is now regarded as much more reliable herbicide for the control of black-grass than it was 10 years ago.