Use your postcode to decide when to spray oilseed rape

Oilseed rape growers can type their postcodes into a website to check whether soil temperatures and moisture levels are correct to apply two key blackgrass herbicides in the autumn.

When a postcode is entered, growers will be shown a traffic light system, with red indicating soil conditions are not right, amber meaning conditions are getting closer, while green signals is it okay to spray.

The two widely used herbicides Kerb Flo 500 and AstroKerb work best when soil temperatures are cooling to about 10C and falling, and the soil moisture deficit is down to 50mm and falling. These conditions normally occur from early November onwards.

David Roberts, oilseed rape agronomist with the products’ manufacturer Dow AgroSciences, says to get the best results, growers need to look at soil temperature, moisture levels and weed seed depth.

“This is to help guide users of these products, but farmers and agronomists need to also assess conditions on a local basis,” he says.

Both post-emergence residual herbicides have a four-month application window from 1 October to the end of January to control blackgrass and some other weeds.

Low soil temperature means the herbicides are slower to break down and so longer persistence for weed control is achieved, while good levels of soil moisture help to distribute the herbicides in the top few centimetres of the soil.

The best control can be achieved with weed seed germinating in the top 50mm of the soil where the concentration of the herbicides is high enough to give good weed kill.

Kerb contains propyzamide, which controls blackgrass and some other weeds, while AstroKerb also contains aminopyralid as well as propyzamide to give control of mayweed species and common poppy.

The postcode system can be assessed via or .

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