Multi-Year Regional Evaluation of One and Two Fungicide Applications for the Management of Target Spot on Two Cotton Varieties

Corynespora target spot (Corynespora cassiicola) is an emerging cotton disease in the Southeastern U.S. Variability among years and geographic location in incidence and severity of target spot suggests disease development is driven by extended periods of rainfall and moisture associated with warm temperatures. Premature defoliation greater than 30% can rapidly follow lesion development leading to yield loss. Fungicides have been observed to protect cotton yield, especially in situations where defoliation exceeds 50%. The objective of this multi-year regional project is to evaluate the effectiveness of various fungicide application programs for managing target spot as well as yield response and lint quality. This study was conducted over 2 years with trials established in 4 locations across 4 states (GA, FL, LA and VA) in 2014, and 7 locations across 6 states (AL, GA, FL, LA, TN, and VA) in 2015. Two varieties (Phytogen 499 and DPL 1137) and four fungicides (Headline® SC, Topguard®, Priaxor®, Quadris®) were evaluated. Fungicide treatments consisted of a single application at disease onset but no later than 5 weeks after first bloom or an application at disease onset 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 and quality were assessed following harvest. Influences of fungicides, number of applications, variety, and interactions among these factors was determined within and across locations. Relationships among environmental factors, disease development, defoliation, and yield loss will be discussed. This study will provide the industry with further insights about development of target spot, and the efficacy of fungicides to manage this disease and protect cotton yields.