UK soya growers gain two valuable pesticide options

UK soya growers now have pesticide options for managing both an important pest and a fungal disease, following the approval of two products.

Up to now, soya growers have had no approved insecticides for bean seed (or Delia) fly or fungicides against sclerotinia in soya beans, says David McNaughton, managing director of Soya UK.

However, Lambdastar (lambda-cyhalothrin) now has an extension of authorisation for minor use (EAMU) for controlling bean seed fly.

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For sclerotinia, growers can now use the strobilurin Azoxystar (azoxystrobin).

Tristan Gibbs, an independent agronomist with Crop Management Partners and a member of the AICC based in Kent and East Sussex, sees the value of the two approvals for the UK soya crop.

“Bean seed fly is a significant issue for soya beans, and since the revocation of Dursban in 2016 there has not been any approved alternative.”

He says as much as a third of the crop can be lost to the pest in any given year.

“However, it’s often not that obvious what has caused the damage – if you don’t find the fly larvae in seedlings it may just appear as a thin crop that has not germinated well.”

Bean seed fly

Female bean seed flies are attracted to soils where there is active microbial degradation of organic matter. The highest risk is following organic amendments, including incorporation of cover crops as well as recently cultivated soils.

Mr Gibbs believes that the best approach is to treat the crop as close to emergence as possible, just as the seedlings are breaking ground, as Lambdastar will repel the flies.

Timing is critical, as the treatment is effective for only 5-7 days – so if the crop does not emerge in that period, the flies will lay their eggs and the larvae will cause crop damage.

“If you are late by just two days with the application, the flies will have already laid their eggs,” says Mr Gibbs.

Sclerotinia

As far as diseases in soya beans go, we get off lightly in the UK – however, Sclerotinia can be an issue, he adds.

“Although it is not a serious threat every year, there is no room for complacency. It is always lurking in the background and in some years could present a serious threat to yields.”

Growers who believe their sclerotinia risk to be high or who like to take a preventative approach can use 0.75 litres/ha of Azoxystar, applied alone or with a post-emergence herbicide, around mid-June, says Mr Gibbs.