Warm weather increases mealy aphid threat

Mealy aphids have made an earlier than normal appearance in oilseed rape crops across eastern and southern England and are heading north, according to UAP and ADAS.

The pest is not usually seen until the end of flowering, but has been encouraged by recent warm weather and levels are building on stems and flowers, said UAP technical director, Chris Bean.

Problems have already been seen in the southwest, Kent, East Midlands and eastern counties, but he expected further reports in northern UK as flowering progressed.

ADAS entomologist David Green said aphid numbers typically build up on the main raceme, particularly on headlands. Spraying is advised when 13% of winter-sown plants are infested, but the threshold is just 4% in spring crops.

“We’ve seen really good results in the past from Mavrik (tau-fluvalinate) on mealy aphids, particularly at this [flowering] stage of the crop,” said Mr Bean. “It is one of the strongest stand alone products for low risk situations, with the added advantage of being relatively benign on most beneficials.”

Where infestations are bad, he recommended using Mavrik at the 200ml rate, perhaps as a partner with pirimicarb. It is also one of the few insecticides approved for mixing with a triazole, he noted.