Management of Tomato spotted wilt virus in flue-cured tobacco with acibenzolar-S-methyl and imidacloprid

Tomato spotted wilt virus (TSWV) continues to be a major production constraint in flue-cured tobacco in Georgia. Pretransplant applications of acibenzolar-S-methyl (Actigard) and imidacloprid (Admire and Provado) were evaluated in field trials, singly and in combination, in four locations in 1999. Acibenzolar-S-methyl was also evaluated for its effect on growth and yield, potential phytotoxicity, and activity against tobacco blackshank incited by Phytophthora parasitica var. nicotianae. Acibenzolar-S-methyl alone and with imidacloprid significantly reduced TSWV incidence in all four locations, but the disease incidence in the imidacloprid-treated plots was lower in only one of the four sites. Applications of acibenzolar-S-methyl starting at 4 weeks posttransplant had no effect on TSWV incidence, size, or yield of tobacco compared with nontreated plots. Acibenzolar-S-methyl did not reduce blackshank in a field trial. In the greenhouse, rates of acibenzolar-S-methyl ranging from 0.25 to 8 g a.i. per 7,000 plants showed reductions in growth that did not seem to be related to rate. Pretransplant applications of acibenzolar-S-methyl were critical to the suppression of TSWV, while initial applications made posttransplant had no effect, suggesting that plants must be protected prior to introduction into the field.