Symptoms and Signs
The nature and severity of leafroll symptoms depend on the virus strain, potato variety, environment, and time and source of infection. Plants with chronic (seed tuberborne) infections are most severely affected. They typically are stunted and appear more erect. Lower leaves roll upwards at the margins, have a stiff leathery texture, and may die prematurely. In contrast, plants that become infected in the current season by aphid vectors of potato leafroll virus normally develop symptoms in the upper (youngest) leaves first; the leaves develop an upright orientation, become chlorotic, and roll upwards. Late-season infections are not always accompanied by symptoms. Potato leafroll virus can cause necrotic netting (net necrosis) in tuber vascular tissue of some varieties, including Russet Burbank.
Comments on the Disease
Potato leafroll virus can be introduced to a potato field by infected seed tubers or by aphids that have fed on infected potato plants. The most efficient vector of the virus is the green peach aphid. Several minutes to hours are required for the aphid vector to acquire the virus, but once the virus has been acquired, the aphid carries the virus for life. Winged aphids carried in air currents spread the virus for long distances between fields, while aphids without wings are important in plant-to-plant spread. Aphid feeding introduces potato leafroll virus into the phloem tissue where the virus multiplies, spreads, and initiates disease. Potato leafroll virus is not transmitted mechanically by machinery or contact with leaves.
Management
Use certified seed tubers. Control sources of the virus, including volunteer potatoes and scattered potato plants that are infected with potato leafroll virus early in the growing season. Complete plant resistance to potato leafroll virus is not available in popular varieties, but many available varieties do not develop tuber net necrosis.
Chemical control of potato leafroll virus is aimed at controlling aphids in order to reduce spread of the virus within a field. Apply insecticides from early to mid-season if aphids and potato leafroll virus are present. Late season vector control may offer no economic benefit if the potato variety is not susceptible to tuber net necrosis. See APHIDS for more information on managing aphids.