Pea aphid and black bean aphid are being found in relatively high numbers but it is the pea aphid that is the primary vector of most viruses.
RIS trap catches of pea aphid have already reached a cumulative total of 131 compared with the 10-year average of 33 and last week PGRO technical officer Becky Ward found aphids on nearly every plant in the crops she walked.
The timing of aphid arrival is early compared to 2015 and crops may be a little behind, many having only been in the ground around three weeks. It is often the aphids that infest the crop early in its growth that transmit viruses and these have more effect at early stages, she said. "It is therefore looking like a high virus risk year and prompt action will be necessary to prevent transmission."
Following re-registration of pirimicarb-containing insecticides, new labels restrict use to a single application at a maximum rate of 280 g/ha. Ward therefore suggests using one of the permitted Biscaya (thiacloprid) sprays now to reduce virus transmission, and saving the pirimicarb spray to reduce feeding damage during flowering and early pod set, saying: "With this year's high aphid pressure outlook a sequence of treatments may be necessary."
Biscaya can be applied twice at 0.4 L/ha with a harvest interval of seven days for both combining and vining peas. Bayer insecticides campaign manager Neil Thompson added that as well as being approved for the control of pea aphids, it reduces damage by pea midge, saying: "In trials it has consistently increased pod number above that achieved from standard programmes of lambda-cyhalothrin and pirimicarb."