There is still plenty of time to apply the residual herbicides ASTROKerb or Kerb Flo 500 in oilseed rape as the spray window doesn’t close until the end of January. This is a great opportunity to interrupt the lifecycle of black-grass with a chemical that works in a different way to those in cereals. Both products work well in December and right the way through to their cut-off date, the 31st of January.
“Many growers see the need to look beyond one crop and plan a more effective black-grass control programme across their whole farm rotation. Kerb Flo 500 or AstroKerb both contain the residual active ingredient propyzamide that works in a completely different way on black-grass to the herbicides commonly used in cereals. So if these herbicides are used to their best effect in rape, there is a real opportunity to reduce the black-grass burden in following cereals. If application conditions are right, farmers can expect levels of black-grass control from AstroKerb or Kerb Flo 500 frequently in excess of 90%, a level that very few graminicides are currently achieving in any crop. We have seen successful results from AstroKerb and Kerb Flo 500 applied in throughout December and January,” says David Roberts of Dow AgroSciences.
“But conditions need to be right and applications should only be made with regard to water stewardship. In other words do not spray when there is any risk of run-off to adjacent watercourses,” warns David.
“Propyzamide in Kerb Flo 500 is soil-acting, so spraying wet weeds at run off or after light rainfall is not an issue. In colder conditions its activity is prolonged and because frosts cause black-grass to throw out more adventitious roots, there is improved uptake of propyzamide. Kerb Flo 500 can be applied in frosty weather. However do not spray onto frozen ground if rain is forecast as this could result in run-off into water courses. Precautions are vital in order to avoid contaminating water. AstroKerb, on the other hand, contains the residual propyzamide plus the contact-acting aminopyralid and so the broad-leaved weeds targeted, poppies and mayweeds, are best controlled when applications are made to a dry leaf. If it rains within one hour after application, efficacy will be reduced. For AstroKerb, wait until the frost is off the weed leaf and the leaf is dry enough.”
David has seen that if you spray Astrokerb in cold conditions, you need to be patient as weeds take a while to die. “Weeds only start to show symptoms and die when active growth recommences. You can also look out for the classic symptoms of propyzamide-affected black-grass, such as swollen stem bases and purple or reddening discolouration. Propyzamide is known to work slowly and it can take up to three months to kill weeds. The herbicide’s activity will not be affected by cold temperatures after application, however.”
He says that this year many oilseed rape crops have dense canopies, with very few crops opened up by frost as yet. “Trials with Kerb Flo 500 demonstrate that a full oilseed rape crop canopy at the time of application makes no difference to the final levels of black-grass control. Astrokerb has contact and root activity on its main broad-leaved weeds, poppies and mayweeds. In our trials, when crop canopies were large, control of these weeds was good. However if, despite our positive experiences you are still concerned, wait until the frost has opened up the crop canopy before you apply these residual herbicides, but do so before the cut-off date.”
David reminds growers that, in order to maximise the efficacy of the residual active propyzamide, soil temperatures need to be below 10°C and falling and the soil should be adequately moist. “You can check your local conditions using the web-based Postcode traffic light tool on the Dow main web site, the LifeCycle web site and also on Farming On-Line, although I would think that most places across the UK now fall well within the right conditions.”
“The ultimate decision to spray must always be based on local conditions, including the ability to travel and the potential risk to watercourses. Maintaining careful Stewardship of residual herbicides in oilseed rape is vital to ensure the long term availability of these important herbicides,” says David Roberts.
