Arable News

  • Written by: Farmers Guide
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Spray window open for Kerb

There is still plenty of time toapply the residual herbicides ASTROKerb or Kerb Flo 500 in oilseed rape as thespray window doesnt close until the end of January, says Dow AgroSciences. This is a greatopportunity to interrupt the lifecycle of black-grass with a chemical thatworks in a different way to those in cereals. Both products work well inDecember and right the way through to their cut-off date, the 31stof January, adds the firm.

Many growers see the need to lookbeyond one crop and plan a more effective black-grass control programme acrosstheir whole farm rotation, says the company’s David Roberts.

Kerb Flo 500 or AstroKerb bothcontain the residual active ingredient propyzamide that works in a completelydifferent way on black-grass to the herbicides commonly used in cereals. So ifthese herbicides are used to their best effect in rape, there is a realopportunity to reduce the black-grass burden in following cereals. Ifapplication conditions are right, farmers can expect levels of black-grasscontrol from AstroKerb or Kerb Flo 500 frequently in excess of 90%, a levelthat very few graminicides are currently achieving in any crop. We have seensuccessful results from AstroKerb and Kerb Flo 500 applied in throughoutDecember and January.

But conditions need to be rightand applications should only be made with regard to water stewardship. In otherwords do not spray when there is any risk of run-off to adjacent watercourses,warns David.

Propyzamide in Kerb Flo 500 issoil-acting, so spraying wet weeds at run off or after light rainfall is not anissue. In colder conditions its activity is prolonged and because frosts causeblack-grass to throw out more adventitious roots, there is improved uptake ofpropyzamide. Kerb Flo 500 can be applied in frosty weather. However do notspray onto frozen ground if rain is forecast as this could result in run-offinto water courses. Precautions are vital in order to avoid contaminatingwater.

AstroKerb, on the other hand,contains the residual propyzamide plus the contact-acting aminopyralid and sothe broad-leaved weeds targeted, poppies and mayweeds, are best controlled whenapplications 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 weedleaf and the leaf is dry enough.

David has seen that if you sprayAstrokerb in cold conditions, you need to be patient as weeds take a while todie.  Weeds only start to show symptomsand die when active growth recommences. You can also look out for the classic symptoms of propyzamide-affectedblack-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 killweeds. The herbicides activity will not be affected by cold temperatures afterapplication, however.

He says that this year many oilseedrape crops have dense canopies, with very few crops opened up by frost asyet.  Trials with Kerb Flo 500demonstrate that a full oilseed rapecrop canopy at the time of application makes no difference to the final levelsof black-grass control. Astrokerbhas contact and root activity on its main broad-leaved weeds, poppies andmayweeds. In our trials, when crop canopies were large, control of these weedswas good. However if, despite our positive experiences you are still concerned,wait until the frost has opened up the crop canopy before you apply theseresidual herbicides, but do so before the cut-off date.

David reminds growers that, inorder to maximise the efficacy of the residual active propyzamide, soiltemperatures need to be below 10C and falling and the soil should beadequately moist.  You can check yourlocal conditions using the web-based Postcode traffic light tool on the Dowmain 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 theright conditions.

The ultimate decision to spray must always be based onlocal conditions, including the ability to travel and the potential risk towatercourses. Maintaining careful Stewardship of residualherbicides in oilseed rape is vital to ensure the long term availability ofthese important herbicides, says David.


  • Written by: Farmers Guide
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