Influence of rate on preventive applications of Quadris for control of target spot on Burley tobacco
Target spot, caused by Thanatephorus cucumeris, is a disease of importance on Burley tobacco in Kentucky, particularly in years with frequent rains and moderate temperatures. Current recommendations for control include sound management practices and properly-timed applications of azoxystrobin (Quadris 2.08 SC). Adequate control of target spot can be achieved with an early (layby) treatment of Quadris at 8 fl oz/A and follow-up treatment if needed prior to topping; this recommendation is supported by four years of testing. However, research has not been conducted to identify the optimal rate of Quadris needed to work within these application timings. In 2009, a study was conducted near Falmouth, KY (Pendleton County) to evaluate Quadris at 6, 8, 10, and 12 fl oz/A in a two-spray program (layby and pre-topping) for management of target spot. At season's end, no differences in severity of target spot were found between any dosage of Quadris and all treatments gave a significant reduction of disease in comparison to the untreated control. Yields, however, were not different between the untreated control and any fungicide treatment. Because these data represent one year's testing at one location, additional research is needed before recommendation of the 6 fl oz/A rate can be justified.