Fungicide Selection and Nozzle Arrangement Impact Target Spot Control and Yield of Cotton

Target spot is an emerging disease in cotton. Studies in southwest and central Alabama in 2013 and 2014 assessed Headline 2.09SC and Quadris 2.08SC efficacy against target spot for improving yield when applied in an over-the-top or drop-nozzle configuration to the susceptible Phytogen 499 WRF and partially resistant Deltapine 1252 B2RF varieties. At three location-years, onset occurred in late July and exceeded 50% defoliation by mid-September; dry weather suppressed disease at the fourth location. Final defoliation was lower for the Headline drop than for the over-the-top nozzle arrangement and lower than Quadris regardless of nozzle arrangement. Despite higher defoliation of Phytogen 499 WRF, both varieties had similar yields at two locations in 2013 and inconsistent yields in 2014. Relative area under the disease curve (relAUC) for defoliation differed by fungicide treatment across location-years. Fungicides increased yields at one location in 2013, with greater yields for the Headline and Quadris drop-nozzle treatments than the control. Across three location-years with >50% defoliation, Headline drop-nozzle treatment improved Phytogen 499 WRF yield compared with no treatment. Despite better control, higher costs and maintenance issues will limit drop-nozzle use. Results show that a partially resistant variety is an effective target spot-management tool.