22 May 1998

Keep aphid-eaters


MAKE sure you keep aphid predators on your side this season to cope with heavy aphid pressure.

That is the advice to sugar beet growers from Alan Dewar of IACR-Brooms Barn. Choosing a predator-friendly aphicide should pay dividends, he suggests.

Aphid-borne virus yellows can slash yield by 50%, warns Dr Dewar. This year the threat is particularly high. For the first time peach potato aphids were caught in Brooms Barn traps in March. "Several other species, including cereal aphids were also caught, so it seems the aphid legions are gearing up for an all out assault on our arable crops."

The predicted June invasion has already begun – in April, he adds.

"The implications of this early infestation are that crops will not be so well developed, and will be more susceptible to aphid damage and virus yellows than they would be if attacked later on."

Many growers may ignore these warnings thinking their crops are protected by Gaucho (imidacloprid) seed dressing, he says. But heavy rains may have denatured the chemical faster than expected. "Growers should be aware that additional treatments may be necessary."

One spray-on product for use this year is Cyanamids Aztec (triazamate). It was approved for use of sugar beet last year but was little needed, he says. Brooms Barn trials show it controls aphids, especially those with esterase resistance, but leaves beneficial insects unharmed because of its systemic action.

Natural control by ladybirds, lacewings and hoverflies is particularly valuable when pest numbers are high, he notes.

MACE peach potato aphids, those containing modified acetylcholinesterase, will not succumb to triazamate or pirimicarb. But the selective action of Aztec should ensure beneficials are not killed off when the crop is sprayed, allowing predators to mop up surviving MACE aphids, he maintains. "Organophosphorus and pyrethroid treatments will not allow this to happen."

MACE aphids ran riot in Lincs potato crops in 1996, recalls Dr Dewar, who is keen to avoid a repeat experience in sugar beet this year. Protecting predator insects should help keep on top of them, he says. "Not much else controls them."

&#8226 Wingless aphids have been reported in most areas, says Brooms Barn. In Suffolk and Norfolk the effect of lower dose Temik (aldicarb) on early-mid March-sown crops is wearing off, and crops should be monitored as untreated, it advises.

Aphids beware …beneficial pest predators could play a key role in protecting sugar beet crops from an early aphid onslaught this season, says Dr Alan Dewar.

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