Soils are moist and soil temperatures have got down to below 10º at 30 cms in many parts of the country, particularly Scotland and northern England. This means that conditions are just about there for optimal performance of the residual herbicide propyzamide, the active ingredient in Kerb Flo and ASTROKerb. Dow AgroSciences are advising growers to make sure that soil temperatures have dropped and soil moistures are appropriate before applying either Kerb Flo 500 or ASTROKerb.
“Propyzamide, in common with other residual herbicides, breaks down quickly in warm soils. If you treat when soil temperatures are too warm, the speed of breakdown may lead to insufficient concentration of propyzamide in the rooting zone of the black-grass, possibly leading to poorer levels of weed control,” warns David Roberts of Dow AgroSciences.
“We have consistently advised growers to wait until soil temperatures have gone down to 10ºC and falling at 30cms depth and when there is sufficient soil moisture in the soil for uptake by the weed. These combined criteria are rarely met in the main rape growing areas until November and they look as if they are beginning to be met in the last few days,” he says. Current local conditions can be checked using the new web-based Postcode traffic light tool on www.myfarmlifecycle.com or on Farming On-Line.
Some agronomists have planned to tank-mix Kerb with a graminicide such as Laser (cycloxydim) to boost black-grass control. As an alternative graminicide, there is much interest in the use of clethodim this season and Centurion Max is compatible with Kerb Flo 500 and ASTROKerb, but keep water volumes at 200 L/ha if mixing, advises David.
He points out that this year with high disease pressure in oilseed rape, an autumn Phoma spray will possibly coincide with Kerb Flo 500 and ASTROKerb applications. “You can mix them with Phoma fungicides including Punch C (flusilazole and MBC), Plover (difenconazole), Proline (prothioconazole) and Sanction (flusilazole). But it should be noted that we do not support three-way tank-mixes of Kerb Flo 500 plus a graminicide and a fungicide for crop safety reasons, especially on overlaps. The three-way mix is at growers’ own risk.”
“In addition to the new on-line traffic light system, we will continue to provide the usual information on soil temperatures and soil moisture deficits on our web site or send it out directly to advisors and growers, as we want to make sure that Kerb Flo 500 and ASTROKerb are given the best chance to work as well as we know they can,” says David.
David says that if application conditions are right, farmers can expect levels of black-grass control from Kerb Flo 500 and ASTROKerb frequently in excess of 90%, a level that very few herbicides in either rape or cereals can achieve. “The best advice is to wait until conditions are right before making applications of Kerb Flo 500 or ASTROKerb to winter oilseed rape. Applications when conditions are not quite appropriate may result in 5% or possibly 10% less control of black-grass. The investment Dow AgroSciences has made in developing and refining advice such as this means that propyzamide is regarded as a reliable herbicide for black-grass control,” he says.
Both ASTROKerb and Kerb Flo 500 have the same wide application window of four months, from the 1st of October through to the end of January. “ASTROKerb delivers the same weed spectrum as Kerb Flo 500 with the addition of mayweeds and common poppy. We would expect activity on sow-thistle and groundsel too,” he says.
“The decision to spray should be based on local conditions, including the chances of travelling, the priority of spraying grass-weeds in winter wheat and consideration of the potential risk to watercourses. Maintaining careful Stewardship of residual herbicides in rape is important to ensure long term availability of these herbicides and every manufacturer, agronomist and grower needs to take their responsibility seriously in this regard,” says David Roberts.
