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CORESTA Meeting, Agronomy/Phytopathology, Montreux,1997, PT4

Tomato spotted wilt virus in Georgia flue-cured tobacco

University of Georgia, Dept. of Plant Pathology, Tifton, GA, USA.
TSWV was not known in Georgia prior to 1986. Since then the disease has increased steadily with some fields suffering >50% loss by harvest. The principal thrips vector is Frankliniella fusca . This thrips feeds on foliage until shortly after top removal then disappears as leaf nicotine levels increase. There is little evidence of F. fusca breeding on tobacco. Thrips tabaci and F. occidentalis are seldom found on tobacco foliage in Georgia. F. occidentalis is fairly common in tobacco flowers where top removal is late or poorly done. Other known vectors of TSWV have not been found on Georgia tobacco. Occurrence of TSWV in the field is random. In field infection rather than use of infected transplants is the major source of disease. Insecticide treatments to control thrips give inconsistent, usually unsuccessful, control of TSWV. Even when successful there is no more than a 50% reduction in disease incidence. Removal of infected plants has not been beneficial. Georgia tobacco is transplanted between 15 March and 20 April with most activity between 25 March and 15 April. Transplant date usually has a significant effect on the incidence of TSWV. The specific time during the transplant period favoring the lowest disease incidence varies from year to year and is not predictable at this time. Diseased plants show up continuously until top removal. Some evidence suggests this is the result of a variable latent period following one or a few episodes of early season infection rather than season long infection. Between top removal and harvest, most symptomatic plants become chlorotic, wilt and die resulting in little or no useful leaf from any infected plant regardless of when symptoms developed.