Reaction of Cotton Varieties to Corynespora Leaf Spot in Alabama

Commercial mid- and full season flex cotton varieties and selected experimental lines were evaluated for their reaction to Corynespora leaf spot.  Dryland and irrigated studies were located at the Gulf Coast Research and Extension and Wiregrass Research and Extension Centers, respectively.  In one study at the former research unit, light to moderate leaf spotting along with minor leaf shed attributed to Corynespora leaf spot was observed in early August.  Disease intensification on all varieties continued until the onset of cooler and drier weather in mid-September.  Final defoliation levels varied from a visually estimated 38% for Stoneville 4288 to 83% for Phytogen 499 with most varieties suffering between 50 and 60% premature leaf shed.  In a second variety trial at the Gulf Coast Research and Extension Center, Phytogen 499, Phytogen 375, Phytogen 565, and DPL 1252 suffered similarly high Corynespora leaf spot-incited defoliation.  Similar differences in the reaction of cotton varieties were noted in an irrigated trial at the Wiregrass Research and Extension Center.  Yields for all field trials are pending.