Winter weather affects influx of aphids

Harsh weather conditions lower pest populations and delay aphids' flying time until late May.

The harsh winter has lowered aphid populations and delayed their flying time, according to latest research by experts at the Scottish Agricultural Science Agency (SASA) and Rothamsted Insect Survey (RIS).

Rothamsted's Dr Richard Harrington said that predicted first capture dates for peach potato aphid at all 16 RIS and SASA suction trap sites in England and Scotland were more than a month later than average.

This means that seed crops planted by the end of April in Scotland and Yorkshire should have about a month without any pressure from the insect before it emerges in late May to early June.

Bayer CropScience's Dr Bill Lankford said that seed potato crops would therefore not need in-furrow treatment because they were unlikely to persist through to the predicted late arrival of potato aphids.

He added: "Growers will need to focus on control of cereal aphids for four to five weeks from crop emergence, and when the colonisers arrive the twin threats will be best managed by alternating sprays of Biscaya with approved pyrethroids."

FORECASTING

Last year's cold December meant that the RIS 2011 potato and vegetable aphid forecasting method had to be revised.

In the past, forecasts had been based on mean temperature in January and February for the strongest correlation with aphid migration timing and size.

"This year, we have based the forecasts on the two coldest winter months, December and January," said Dr Bill Lankford of Bayer CropScience. "It is unlikely that aphids that overwinter predominantly in mobile stages will have survived the very cold December."

Updates on aphid activity can be found on the RIS or SASA websites.

ROSE GRAIN APHIDS

Rose grain aphids, which overwinter mainly as eggs rather than in mobile stages, will hardly have been affected by the harsh conditions. Growers should therefore expect to see them start to fly during May and build up to peak numbers in July as usual.

One of the first findings of the Potato Council-funded research project named Aphids & Virus Transmission in Seed Crops was that rose grain aphids were the most likely vectors of the non-persistent viruses PVA and PVY. Non-persistent viruses were passed onto the plants by the insects when they fed on them.

Last year, some areas of Scotland were overwhelmed with the rose grain aphids and the incidence of PVY symptoms recorded in crops jumped to 15 per cent.

Another early finding of the project - whose consortium members include the Scottish Crop Research Institute, the Food & Environment Research Agency and the Scottish Agricultural College - was that mineral oils could give growers a control method that prevented the non-persistent virus from spreading. However, an investigation of how such oils would work with insecticides such as neonicotinoids is needed.

Bayer CropScience's Dr Bill Lankford has warned growers not to experiment with mineral oils just yet: "In tests with one mineral oil, adding Biscaya produced phytotoxic effects and increased virus symptoms. We cannot yet support tank mixture with mineral oil and recommend Biscaya is used in alternation with other oil-containing treatments."


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