44th TWC, Tob. Work. Conf., 2010, abstr. 24

Evaluation of a simulated transplant-water application of Ridomil Gold for management of black shank in Burley Tobacco

University of Kentucky, Plant Pathology Dept., 1405 Veterans Drive, Lexington, KY 40546, USA

Black shank, caused by Phytophthora nicotianae, is the most damaging disease of Burley tobacco in Kentucky. Along with sound cultural practices, soil applications of mefenoxam (Ridomil Gold, or RG) are also recommended. Although effective, RG is an expensive tool whose cost can dissuade growers from using it. To lower overall cost of application while maintaining acceptable control of disease, studies were conducted in 2008 and 2009 to evaluate the efficacy of RG SL against black shank when applied in transplant water at full and reduced rates. In 2008, RG EC and RG SL were applied as drenches immediately after transplanting (simulated transplant-water volume of 300 gal/A) at 0.5, 1, and 2 pt/A to assess phytotoxicity and suppression of disease. At season's end, no differences in black shank incidence were observed between formulations or rates of RG, and no phytotoxicity was noted; yield was increased 20-30% over the untreated control. In 2009, RG SL was drench-applied at rates of 0.25, 0.5, and 1 pt/A to varieties KY14 X L8, TN 90, KT 204, and KT 209'. These treatments were compared to RG SL (1 pt/A) broadcast-applied to soil pre-planting (PP), PP + 1st cultivation + layby, or 1st cultivation + layby. Drench-applied RG SL at 0.25 pt/A followed by broadcast-applied RG (1 pt/A) at 1st cultivation, layby, or both timings were also included. Across varieties, post-transplant drenches of RG SL at 0.5 or 1 pt/A gave similar control of black shank as broadcast-applied RG SL. Drench-applied RG SL at 0.25 pt/A followed by soil-directed RG SL did not differ from the soil-directed treatments alone. No significant differences in yield were found between treatments. Use of RG SL in transplant water may offer an acceptable substitute for broadcast-applied RG SL; however, rates below 0.5 pt/A may not provide adequate suppression of disease.