- Peach potato aphid
Transmission of viruses can cause serious economic damage but only heavy infestations cause direct feeding damage. Peach potato aphid, Myzus persicae, is the most important vector of turnip yellows virus (TuYV), potato leaf roll virus (PLRV), potato virus A (PVA) and potato virus Y (PVY). It also transmits cauliflower mosaic virus (CaMV), beet yellows virus (BYV), beet chlorosis virus (BChV) and beet mild yellowing virus (BMYV). If aphids transmit viruses early in the season, effects are greatest. Aphid honeydew can damage quality especially in horticultural crops.
The average yield loss from TuYV in oilseed rape is 15% but it can be as high as 30%. TuYV infection does not usually show until late spring/early summer in OSR and appears as purple tingeing of leaf edges and pods. In vegetable brassicas and lettuce, the peach–potato aphid is a contaminant, can transmit viruses and, in cases of severe infestation, may cause severe distortion of the plant. In sugar beet, beet yellowing virus symptoms are characterised by diffuse chlorotic patches on mature leaves, which expand and coalesce.
The wingless peach–potato aphid is medium-sized and pale green to pink or almost black. The winged form is a similar size but has a black central abdominal patch on the upper surface with a pale underside.
Check if aphids are present before applying treatment.
Insecticide resistance to organophosphates, carbamates and pyrethroids is widespread. Pymetrozine (Plenum)* or thiacloprid (Biscaya) are still effective. Do not make repeat applications of any insecticide if it appears not to work at the full recommended rate and it has been applied correctly; use an alternative. Tank mixtures of two different aphicide chemical groups may improve efficacy.
* Please note that pymetrozine (Plenum) is currently being banned - the ban on use will be implemented from January 2020.
It is no longer permissible to plant oilseed rape seed treated with the neonicotinoids clothianidin, imidacloprid or thiamethoxam. Plenum and Biscaya can be applied once in the autumn for controlling aphids that spread TuYV in oilseed rape.
For potatoes, using seed potato certified by the British Seed Potato Classification Scheme reduces the virus risk and its subsequent spread by aphids. Potato varieties differ in their susceptibility to aphid infestation and virus infection. It typically takes 10-14 days for the virus to spread from the original infection into the tubers. Growers can take advantage of this and desiccate crops where a late-season increase in aphid numbers has occurred.
Natural enemies include parasitic wasps, ladybirds, predatory flies, spiders, ground beetles, rove beetles, lacewings and insect-pathogenic fungi. Providing habitats that encourage the presence of these can help control aphid numbers. They may not be effective in preventing virus transmission, as this can occur even at low aphid densities.
Early sowing of sugar beet can mean it is less likely to be affected, as older leaves are less palatable to the aphids