Potato Leafroll Virus
Visible symptoms vary according to plant variety, environmental conditions and type of infection. Primary infection, which is caused by aphids, is visible mostly on younger leaves. The margins start to roll upwards and become dry, pale or develop interveinal chlorosis. In plants grown from a contaminated tuber (secondary infection), older leaves are upturned, stiff and brittle with a purple or red underside, while younger ones are upright and pale green or chlorotic. The plants growth is stunted and the stalks are stiff and point upwards. High infection levels reduce tuber yield and marketability.
Initial transmission occurs when plants get infested and fed upon by virus-carrying aphids during the growing season. Secondary infection takes place when contaminated tubers are planted, and potato plants grow from them. Aphids transmit the infection to other healthy plants. The virus is persistent for the life of the aphid, so the potential of infection is high. To transmit the virus, the insects need to feed on the plant for at least 2 hours. Humid soil promotes the risk of infection.
Direct treatment of the virus is not possible, but reducing aphid population by means of predators or parasitoids is a helpful preventive measure. Ladybirds, soldier beetles, lacewings, and some types of midges and flies eat adults aphids and larvae. Parasitic wasps could also be used.
Always consider an integrated approach with preventive measures together with biological treatments if available. Chemical treatment of viral diseases is not possible. However, a the aphid population can be controlled to some degree. Apply neonicotinyl insecticides in the early phases of crop growth for example.