Beetle is threat to brassica crops

Leading insect expert Dr Rosemary Collier has warned growers that a pollen beetle resistant to pyrethroids could pose a threat to brassica crops.

Collier, an entomologist based at Warwick HRI Wellesbourne, revealed at the biennial Brassica Growers' Association (BGA) conference earlier this month that pollen beetles resistant to pyrethroids - a pesticide that has been used by growers for more than 20 years - could spread to UK brassicas from rape crops.

The beetles currently affect two-thirds of oilseed rape areas in Europe and destroyed 30,000ha and damaged 200,000ha of winter oilseed rape in Germany in 2006.

They were first detected in the UK in the same year and by 2007 had spread to most coastal areas of East Anglia and the South. This year they could spread to other parts of the country.

Collier said: "It is a potential problem. The beetles will move from rape to horticultural brassicas quite easily. They are mobile insects and if they do move to brassicas it is usually in midsummer."

She told Grower after the conference that the bugs overwinter as adult beetles before moving into rape crops in spring when they complete their life cycle.

"The new adult beetles that emerge in midsummer fly off to various places - they basically need to feed before they overwinter. This is when you find them in horticultural brassicas among other things. So if there are resistant beetles in nearby rape, there could be resistant beetles in horticultural brassicas.

"Pollen beetles haven't been a major problem in horticultural brassicas for quite a few years. However, if they were, and there was a good proportion of resistant ones, they might be difficult to control with pyrethroids."

The problem is of such concern to the Home-Grown Cereals Authority (HGCA) that it last week warned oilseed rape growers to restrict the use of pyrethroids. HGCA research manager Vicky Foster said: "Without prompt action to combat resistance there is a high risk that it will become more widespread."

She also advised growers to alternate pyrethroids with other insecticide groups still unaffected by resistance.

Collier echoed these sentiments [at the BGA conference] by advising growers to "keep evaluating non-insecticidal alternatives such as physical barriers".

In particular, she advised growers to use neonicotinoids - which control aphid infestations - carefully to prevent the insects from building up resistance.

A LINK project - ongoing since 2004 and led by Rothamsted Research - has shown that neo-nicotinoids are still proving to be effective in controlling the aphids.

However, further research from the project has shown that an increasing number of aphids in the UK are becoming resistant to pirimicarb. Some 90 per cent of the aphids detected last year by the Rothamsted suction trap at Kirton carried the pirimicarb - or MACE - resistance, and approximately 40 per cent had both MACE resistance and kdr (pyrethroid) resistance.

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