26 October 2001

Scotlands oilseed rape growers on aphid alert

OILSEED rape growers in Scotland are being advised not to be panicked into spraying nicotine-based sprays to control aphids.

Although products like NicoSoap now have an off-label approval for rape, after evidence of MACE-resistant aphids in crops in Fife and Angus, it should only be used as an emergency treatment, says SAC Aberdeen entomologist Collette Coll. "Its use should be avoided unless your crop is actually dying out."

Nor should seed potato growers be worried about resistant aphids surviving the winter and moving into next years crop, she says. "Resistant aphids have a high level of esterase, which for some reason makes them less able to stand cold temperatures. They are also less able to successfully reproduce."

But that is cold comfort for Scottish-based UAP agronomist Neil Ross. "We have never had an aphid infestation like we have now."

Some of the rape crops he has inspected have 75-80% coverage of aphids. "You can barely see the underside of leaves. The crop is going yellow and dying."

Part of the difficulty is the sheer volume of aphids, a unique occurrence this year, says SAC Edinburgh entomologist Andy Evans. "An unprecedented number of winged aphids have been caught in traps."

These have migrated into the rape crops and multiplied furiously in current warm conditions. "The resistance problems have come about from the reliance by seed potato growers on pyrethroids and pirimicarb insecticides."

But there is growing evidence that crops treated with Chinook (imidacloprid + betacyfluthrin), the new seed treatment from Bayer, have escaped the aphid invasion. "Where those aphids are migrating from potatoes to oilseed rape, Chinook-treated crops appear to have been protected," says Dr Evans.

That is no surprise to Bayer, which reports around 50% of the UKs rape crop was treated with the dressing in this, its first year. "Imidacloprid as Gaucho has been relied on for many years to keep aphids out of sugar beet," says the firms Richard Lloyd.

The dressing has replaced Lindane (gamma-HCH), which was banned in 1999. The main target of the dressing is flea beetle. &#42

Pleased with Chinooks flea beetle control in East Anglia is Dalgety agronomist James Potter, here comparing flea beetle damage on volunteer rape (foreground) with healthy Chinook treated rape alongside. Elsewhere the product seems to be offering benefits on aphid control too.