POTATO AND brassica crops are at risk from exceptionally high numbers of aphids this season, experts have warned.

High numbers of the peach-potato aphid (Myzus persicae) have been reported two to three weeks earlier than normal and up to a third of those tested in Suffolk were MACE resistant, said Rothamsted’s Steve Foster.

“Numbers are not unprecedented – in 1996 we saw a lot, particularly in the east – but this year we are finding aphids several weeks earlier.

“With the current levels of aphid activity growers could be facing unprecedented numbers of MACE aphids come the autumn, unless they start to take action now.”

Numbers of M.persicae are “some of the biggest ever seen”, particularly in South Lincolnshire, Norfolk and Suffolk, added agronomist John Keer.

Both experts agree that the incidence of MACE resistance is high, particularly in the east, and growers need to closely monitor the efficacy of products applied.

“Every crop can be different, so growers need to check each field. I am aware of one situation where a straight Aphox (pirimicarb) application in brassicas has done nothing at all,” said Mr Keer.

He believes resistant aphid numbers are high enough this year that potato growers should use Plenum (pymetrozine) – to which there is no known aphid resistance.

Even though it is slightly more expensive than other products, its use will be worthwhile this season agreed Dr Foster.

Growers must refresh themselves with information on aphicide resistance, threshold levels in line with grower protocols and the latest Insecticide Resistance Action Committee guidelines, added the British Potato Council’s Rob Clayton.

Further information on this can be found on the BPC’s website, www.potato.org.uk.

Keep up-to-date with pest and disease pressures with FWi’s Crop Watch section – see Special Reports – Plant Health – Crop Watch.