Reaction of Cotton Cultivars and Breeding Lines to Areolate Mildew in Alabama

Trials were conducted at the Brewton Agricultural Research Unit (BARU) and Prattville Agricultural Research Unit (PARU) to assess cotton cultivar reaction as influenced by an umbrella fungicide program to target spot. However, areolate mildew was present and fungicide response data was collected. The experimental design was a factorial arranged in a split plot with the nine cotton cultivars as whole plots and a 8 fl oz/A Priaxor + 1.5 pt/A Bravo Ultrex umbrella fungicide program as the split plot treatment. At BARU, Stoneville 6182 GLT suffered higher target spot-incited defoliation than the remaining eight cultivars with the least defoliation recorded for Stoneville 5115 GLT, which was matched by all remaining cultivars except PhytoGen 450 W3FR and Stoneville 4946 GLB2. A significant cultivar × fungicide interaction indicated that cultivar response to the fungicide program differed. At PARU, the umbrella fungicide program gave effective disease control but a significant cultivar × fungicide program interaction was noted. Overall, the high defoliation levels on Stoneville 5020 GLT and PhytoGen 490 W3RF were matched by PhytoGen 340 W3RF, PhytoGen 450 W3RF, and Deltapine 1646 B2XF. In contrast, similarly low defoliation levels for Deltapine 1538 B2XF and Deltapine 1553 B2XF were noted for Stoneville 5115 GLT and Stoneville 4949 GLT. At the Wiregrass Research and Extension Center (WGREC), 44 and 40 commercial and advanced breeding lines screened in the early and full season flex OVT trials, respectively, were evaluated for their reaction to areolate mildew. Areolate mildew was the primary disease in the later planted early flex OVT. Sizable differences in defoliation due to areolate mildew in both OVT trials will be discussed. Yields and grades will be presented for the cultivar × fungicide studies but those values for both WGREC OVT trials were lost.