ROLE OF GREEN PEACH APHID FLIGHTS IN THE EPIDEMIOLOGY OF POTATO LEAF ROLL DISEASE IN THE COLUMBIA BASIN

Three distinct and highly predictable green peach aphid (GPA) (Myzus p ersicae) flights that occur seasonally in the spring, summer, and fall were detected at a southern, central, and northern location in the Co lumbia Basin of the Northwestern United States. Intensity and timing o f the flights was approximately the same at the three locations. Timin g and number of alatae captured in the spring and summer flights was a ssociated with heat unit accumulation. The spring flight, which origin ates on the overwintering peach tree host, colonized but did not intro duce potato leafroll virus (PLRV) into virus-free potato plots. The su mmer flight, which originates from volunteer potatoes and spring herbs originally colonized by the spring flight, did introduce PLRV into vi rus-free potatoes. The fall flight was too late to affect potato produ ction. When plots contained a point source of PLRV, the virus spread r apidly in a plant-to-plant mode to all plants in plots after aphids ar rived in the spring. Rate of spread from point sources of infection wa s not affected by timing or intensity of the spring flight, but timing of virus spread in the plots depended on time of arrival of the aphid s. Once PLRV was introduced to virus-free plots by the summer flight, virus spread to other plants within the plots. GPA overwintered on pea ch trees. Although GPA apterae and alatae were present on winter annua l weed and crop hosts in the fall, none survived winters on these spec ies. In addition to the GPA, one other vector of PLRV, Macrosiphum eup horbiae, was rarely collected in aphid traps. These results suggest th at chemical control of aphids could be delayed until mid-July if PLRV- free potato seed were available.