Aphid pressure could hit OSR yields

Crops treated with second-generation neonicotinoid-based seed treatments should fare better but even so there are signs seed treatments have, in places, been swamped by the very high aphid numbers carrying the virus, says Broom’s Barn crop protection leader, Mark Stevens.

Some 30 per cent of all myzus persicae (peach potato aphids) caught prior to Christmas, were carrying TuYV, he adds.

“Symptoms of TuYV infection were being picked up in crops at the end of November. We’d not normally expect to see these until the spring, indicating that the aphids infected plants early in these crops and that autumn conditions were ideal for the virus to build-up in plants leading to symptom expression before Christmas.”

While the cold start to the year will have helped kill off 99 per cent of these aphids, unfortunately the damage has already been done and growers should expect to pick up symptoms in crops in the spring,

Virus hot spots have been identified around The Wash and Kent, together with a coastal area of Dorset.

“The autumn HGCA trapping work focused on 13 sites across the UK, so although this is a relatively small sample size, it gives an indication of aphid and virus level on a local scale,” says Dr Stevens.

Crop damage this spring could be a lot worse but for the widespread uptake of seed treatments Cruiser OSR (thiamethoxam + fludioxonil + metalaxyl) and Modesto (clothianidin and beta-cyfluthrin) seed treatments last summer.

Trials at Broom’s Barn suggest that current oilseed rape varieties have little obvious in-built resistance to TuYV damage. “Growers need to be aware that while some varieties may express the symptoms in a slightly different way, any inter-veinal purpling or reddening of leaves may not be due to the cold winter, but TuYV,” says Dr Stevens.

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