Impact of Planting Date and Seeding Rate on the Severity of Target Spot in Cotton

Seeding rate and planting date studies were conducted at the Gulf Coast Research and Extension Center and Field Crops Research Unit, respectively. A factorial design arranged as a split-split plot with variety (Phytogen 499WRF and Deltapine 1555B2RF) as the whole plot, seeding rate of 2, 3, and 4 seed/ ft of row as the split plot, and fungicide program as the split-split plot for the former and an early May or June planting date as the whole plot, variety (Phytogen 499WRF, Phytogen 444WRF, and Deltapine 1538B2XF) as the split plot, and fungicide program as the split-split plot for the latter. The fungicide program consisted of four applications of Headline SC at 9 fl oz/A or Priaxor at 6 fl oz/A beginning at first bloom on a 14 day schedule and a non-fungicide treated control. Both studies were irrigated.  Overall, rainfall totals were higher at the former than latter site. In the seeding rate study, final defoliation differed by variety and fungicide program but not seeding rate. Defoliation was greater regardless of fungicide program on Phytogen 499WRF than Deltapine 1555B2RF.  Drier weather suppressed target spot at the Field Crops Research Unit.  Significant planting date × cotton variety, planting date × fungicide program, and variety × fungicide program interactions for defoliation were noted. For the non-fungicide treated control and Priaxor program, defoliation was higher in the June- than May-planted cotton. While no differences in defoliation were noted between varieties planted in May, June-planted Phytogen 499WRF suffered greater defoliation than Phytogen 444WFR and Deltapine 1538B2XF, which had similarly lower defoliation ratings. On all varieties, reduced defoliation was obtained with the Priaxor program than the non-fungicide treated control. The impact of seeding rate, planting date, variety selection, and fungicide inputs on yield will be discussed as will the impact of weather on disease development.