Fungicide sensitivity of corynespora cassiicola and assessment of management of target spot of cotton in Georgia
Laurel, Ma. Katrina Shiela Estrada
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Target spot, caused by Corynespora cassiicola, is a serious foliar disease of cotton in the southeastern United States. Baseline (current) isolates of C. cassiicola were tested for sensitivity to metconazole (DMI), fluxapyroxad (SDHI) and pyraclostrobin (QoI). Further work compared fungicide sensitivity of C. cassiicola isolates from cotton to isolates from other hosts. Field experiments were conducted to establish a relationship between fungicide sensitivity in laboratory experiments and fungicide efficacy in managing target spot on cotton. Based on the sensitivity distribution, all isolates tested were considered sensitive to fungicides. However, these sensitivities varied among isolates offering an early indication that resistance can happen in the future. Additionally, all fungicides reduced disease severity and premature defoliation; however, Priaxor (pyraclostrobin + fluxapyroxad [QoI + SDHI]) proved to be most effective. Results from this study can help optimize fungicide sensitivity monitoring practices in an effort to improve fungicide use patterns for optimum disease management.