Regional Evaluation of One and Two Applications of Registered and Experimental Fungicides for the Management of Target Spot on Two Cotton Varieties

Corynespora target spot (Corynespora cassiicola) is an emerging disease of cotton in the Southeastern U.S. Variability among years and geographic location in incidence and severity of target spot suggests disease development is driven by both moisture and high temperatures. Leaf drop rapidly follows lesion development, and high levels (>30%) of premature defoliation result in yield loss. Yield responses to foliar fungicide applications are not typically reported for cotton, but preliminary studies suggest that in the presence of target spot, fungicides slow down disease development, delay defoliation, and protect yield. The objective of this multi-state project is to evaluate the effectiveness of single and two application programs of selected registered and candidate fungicides for managing target spot as well as yield response and lint quality. In 2014, trials were established in seven locations in six states (AL-2, GA, FL, MS, LA, and VA). Two varieties hypothesized to vary in susceptibility to target spot (Phytogen 499 and DPL 1137) and four fungicides (Headline® SC, Topguard®, Priaxor®, Quadris®) were evaluated.  Fungicide treatments consisted of either a single spray at first bloom or a spray at first bloom followed by a second spray 14 days later. Treatments were applied to field plots in a full factorial, randomized complete block design with 2 varieties, 2 application timings, and 5 fungicide treatments (4 fungicides plus an untreated control).  Disease onset, incidence, and defoliation were evaluated bi-weekly following the first observation of lesions. Lint yield was determined following harvest. Influences of fungicides, number of applications, variety, and interactions among these factors were determined within and across locations. Relationships among environmental factors, disease development, defoliation, and yield loss will be discussed. This study provides additional data on which to base recommendations for management of target spot in cotton.