Growers advised to be vigilant as hot weather increases threat posed by aphids

Aphid numbers are rising and numbers could rocket in the warm, settled weather, according to agro- nomists.

They reminded growers that early summer pest invasion in pea crops can cause yield-robbing physical crop damage and spread viruses - while potato seed crops remain susceptible to virus transmission.

The Processors and Growers Research Organisation (PGRO) technical director Anthony Biddle advised that if there was more than one aphid per four plants on peas then growers should start treating their crops to avoid pea enation mosaic virus transmission and direct feeding damage.

He said: "Spraying with Aphox should sort the problem out. But, if you are combining pea moth control, add some Hallmark Zeon or switch to Dovetail, which contains both actives."

Pea moth thresholds were recently breached in the east and Essex and high catches were predicted as the weather warms.

Biddle added that vining pea growers should also watch out for pea midge. "We have seen the first emergence in north Cambridgeshire and this will be followed by Yorkshire. Sprays need applying at the enclosed bud stage, so later drillings will be most prone."

Potato growers should keep a close eye out for aphids, which are poised to migrate into crops during warmer, drier weather, warned Scottish Agricultural College potato agronomist John Sarup.

Peach-potato aphids, the most important vector of potato viruses, have already been found in yellow water traps on the Yorkshire Wolds.

Sarup said: "Numbers and species need to be monitored carefully - either by using water traps or checking the status in your area by using the Potato Council/Food & Environment Research Agency (FERA) aphid monitoring service on the Potato Council website."

Other species need watching too. Many non-colonising aphid species, particularly bird cherry-oat aphids, carrot willow aphids and rose-grain aphids can also transmit PVY as well as PVA and V.

Seed growers should use a protectant programme to prevent aphids landing on the crop, spraying every seven days from rapid canopy expansion onwards where there is risk of infection.

"Actara works well and controls resistant aphids, plus a tank mix with Hallmark Zeon adds aphid repellent benefits," said Biddle. "But you can only use two neonicotinoids in a seed crop per season - or one in ware crops - so you will have to use other chemistry at some point to partner Hallmark."

Sarup added that, on ware crops, growers should start spraying when a significant increase in aphid numbers on leaves is recorded.

Syngenta insecticides technical manager Michael Tait added that Actara should be applied outside the potato flowering window. "When using any foliar insecticide in crops where bees may forage, follow the stewardship guidelines as prescribed by the British Beekeepers Association and contact your local bee liaison officers," he advised.

The PGRO pea moth telephone service on 01780 783099 can provide specific information about spray dates.

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