Twin spray needed for damaged oilseed rape crops

Oilseed rape growers are being urged to apply two flowering sprays to prevent flea beetle damaged crops succumbing to disease.

Many crops in eastern England hit by cabbage stem flea beetle larvae are showing variable growth and could be more susceptible to sclerotinia.

Current dry weather is likely to extend the flowering period and so two sprays, and perhaps even three, may be needed this season for pest-ravaged crops.

“With the flowering period expected to be extended, then a two-spray strategy is advisable,” says David Leaper, seed technical manager at distributor Agrii.

See also: Oilseed rape damage could heighten sclerotinia disease risk

With plenty of sclerotinia inoculum around, the best advice is to spray at early flowering and then mid-flowering or around three weeks apart, experts says.

Typical sclerotinia treatments

  • Skyway – SDHI bixafen + azoles prothioconazole and tebuconazole
  • Pictor – SDHI boscalid + strobilurin dimoxystrobin
  • Symetra – SDHI isopyrazam + strobilurin azoxystrobin

Many growers have moved to a two-spray strategy but those looking to save costs are warned of the danger of slipping back to a one-spray regime.

Mark Hemmant, technical manager at distributor Agrovista, says crops damaged by flea beetles and pigeons would benefit from two sprays.

“Modern sclerotinia sprays give a yield response even if crops don’t get sclerotinia,” he says.

Experts say that of the products available the SDHI/azole and SDHI/strobilurin combinations are often the most effective and give a “greening” effect as well as controlling disease.

In this the first season of the European Union ban on neonicotinoid insecticide seed treatments due their alleged harmful effect on bees, flea beetle numbers were four times normal levels.

Steve Ellis, entomologist at crop science crop Adas, says oilseed rape crops drilled early and late appear to have suffered less from flea beetle than those in the middle drilling period of around the end of August into early September.