44th TWC, Tob. Work. Conf., 2010, abstr. 116

Influence of agronomic practices on the severity of target spot in Burley tobacco

University of Kentucky, Dept. of Plant Pathology, Lexington, KY, USA

In recent years, target spot (TS), caused by Thanatephorus cucumeri s, has become a serious problem on Burley tobacco when conditions favor the disease. It has been observed that heavy losses are more likely in fields where previous outbreaks of the disease have been observed and crop residue is known to harbor the pathogen. Where tobacco is grow under reduced tillage, a system gaining in popularity, crop residues are generally left intact. This could provide an overwintering site for T. cucumeris , leading to an increase in inoculum and disease in following years. Additionally, cover crop residues favor pathogen development by lowering soil temperatures and increasing soil moisture - factors that promote growth of T. cucumeris and production of spores that will initiate epidemics of TS. In some locations in Kentucky, levels of TS have been believed to be higher in no-till tobacco than in that grown conventionally; however, no work has been done to support these observations. Published reports also implicate low nitrogen levels as factor that increases susceptibility of tobacco to TS, although no definitive studies have been carried out to support this. A study was conducted in 2008 and 2009 to evaluate the combined effects of tillage type (conventional vs. no-till) and nitrogen rate on the severity of TS on Burley tobacco and on yield. In both years of the study, severity of TS decreased with increasing rates of nitrogen. In terms of disease, a small but significant increase in TS severity was seen in no-till plots compared to conventional tillage in 2008 but not 2009. Yields did not differ in either year between no-till and conventional tillage; however, higher rates of nitrogen were associated with higher yields. Additional research is needed to determine if no-till tobacco is inherently more at risk to TS.