17 May 2002

Red alert for resistant aphid crisis

GROWERS could be facing a MACE-resistant aphid epidemic after one of the problem pests was caught at Kirton, Lincs, last month.

The unusually early catch means control strategy could need revising and increased vigilance is a must, particularly for potato growers, says IACR-Brooms Barn.

"We havent caught one so early before, and one aphid caught can represent a lot more in crops," warns IACRs Alan Dewar. "We dont regard this as a fluke."

Growers should be on the lookout for signs that aphids are not responding to carbamate insecticides, such as pirimicarb, he says.

The Kirton area suffered an epidemic of the Modified AcetylCholinEsterase resistant bugs in 1996, causing severe damage to potatoes, he adds.

"If it [MACE resistance] is confirmed by subsequent trappings, growers in the area should avoid pirimicarb altogether."

However, BPC agronomist Rob Clayton urges growers to consider application problems before jumping to conclusions about poor control.

"Well be sending Insecticide Resistance Action Group (IRAG) guidelines out to growers next week."

The risk of virus infection is likely to be no higher than any other year since volunteer potato populations, a common harbour for viruses, are generally lower, he adds.

In general aphids are turning up 20-30 days earlier than the long term mean, colonising crops when they are particularly vulnerable to the viruses they could be carrying, warns IACR Rothamsteds Richard Harrington.

"Many sugar beet crops emerged late because of capping so are even more susceptible."

Dr Dewar says Gaucho-treated (imidacloprid) crops should still be protected, dry conditions in April possibly giving even longer cover than the expected 10 weeks.

However, Temik (aldicarb) only lasts 6-7 weeks, he warns, and untreated or unprotected sugar beet should be sprayed if the threshold of one green wingless aphid per four plants is breached.

&#8226 For more on aphid advice and resistance, see Arable, May 10 and Apr 5 or visit www.pesticides.gov.uk/committees/resistance/irag.htm. &#42

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