Integrated Pest Management to control Areolate Mildew and Target Spot on Alabama Cotton

Abstract

The goal of this project was to improve current management recommendations for two of the most damaging foliar diseases of cotton, areolate mildew (caused by Ramularia gossypii or R. pseudoglycines.) and target spot (caused by Corynespora cassiicola), in the southeastern cotton belt. If not controlled, these two diseases can cause premature defoliation and yield losses of more than 224 kg/ha and 560 kg/ha, respectively. Current management recommendations for areolate mildew and target spot include fungicide applications, cultivar selection, and several cultural practices. In the US, one to two applications of a single-site fungicide such as demethylation inhibitors, succinate dehydrogenase inhibitors, and quinone outside inhibitors are currently recommended. However, seven to eight applications are required to manage areolate mildew in Brazil. Thus, four different fungicides applied one or two times between the first- and fifth-week of-bloom were evaluated against areolate mildew and target spot as well as their influence on yield in central Alabama. Results demonstrated that mefentrifluconazole + fluxapyroxad + pyraclostrobin applied at third- or fifth-week-of-bloom and azoxystrobin applied at the first- and third- or at the fifth-week-of-bloom significantly reduced disease severity and provided economic returns of $398.06/ha and $950.29/ha respectively when compared to the nontreated control. To reduce fungicide inputs, the response of 18 selected commercial cultivars to areolate mildew and target spot were evaluated as influenced by fungicide. Deltapine 1646 B2XF and Deltapine 2127 B3XF were highly susceptible to both diseases; however, fungicide applications significantly reduced disease severity. Deltapine 2020 B3XF and Stoneville 5091 B3XF were tolerant to areolate mildew whereas Phytogen 400 W3FE, Phytogen 480 W3FE, and Deltapine 2012 B3XF were tolerant to target spot. Deltapine 1840 B3XF were tolerant to both diseases. This study shows ii that tolerant cultivars can reduce fungicide input costs and mitigate areolate mildew and target spot incited yield losses. Since previous research has shown that cultivars can vary in susceptibility to different Ramularia spp., the goal of this study was to isolate and characterize Ramularia populations associated with areolate mildew on upland cotton in Alabama. Due to its slow growth in vitro, modified V8 agar and modified Kirchoff’s media coupled with a serial dilution technique reduced contamination and improved the isolation of Ramularia. Based on ITS sequencing, all ten isolates collected from Macon and Elmore County were identified as R. gossypii; however, additional surveys are required.