Imidacloprid insecticide slows development of Pierce's disease in bunch grapes
Six cultivars of bunch grapevines Vitis labrusca (L.) and V, vinifera (L.), 'Cabernet Franc', 'Canadice', 'Flame Seedless', 'Johannesburg Riesling', 'Mars' and 'Reliance' when treated at planting and for 3 yrs with two (early spring and mid-summer) applications of imidacloprid (Admire(R), Bayer Corp., Kansas City, MO) in a 1 to 2 liters aqueous solution (0.70 g active ingredient per vine per application) as drench to the base of the vine, had lower incidence of Pierce's Disease (PD) than untreated grapevines. Apparent PD symptoms were evident on the control vines in mid-summer of the second season. By the fall of the second season and spring of the third season, some control vines were dead. ELISA tests in July of the third season, indicated that similar proportions of treated and control vines contained the PD bacteria. ELISA tests in August of the third season, indicated that significantly more control vines than treated vines contained PD bacteria. Vines treated with imidacloprid showed PD symptoms in June of the third season, and the rate of disease development was slower than in the control vines. After 3 yrs, 18% of the control vines were dead while all the treated vines were alive. 'Carbernet Franc' and 'J. Riesling' vines treated with imidacloprid had higher yields that the untreated vines within the two cultivars in the third season. 'Reliance' vines had higher soluble solids in vines treated with imidacloprid than in untreated vines. Survival at bud break of the fourth year was higher in treated than in untreated vines. Homalodisca coagulata (Say), H. insolita (F.), Oncometopia orbona (Walker) and Graphocephala versuta (Say) were the more abundant leafhopper vectors of PD in the experimental plot and in the surrounding fruit crops. Overall, this research suggests that under severe PD pressure vineyard life can be extended by about 1 yr by application of imidacloprid.