Evaluation of systemic fungicides and dormant spray applications in pecans and implications for disease management
Brown, Kyle Adison
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Pecan scab, caused by the fungal pathogen Fusicladium effusum, is the most severe disease of pecan in the southeastern United States. Fungicides are an essential tool to reduce losses, and the movement of systemic fungicides, as well as benefits of dormant sprays was investigated. Field experiments demonstrated the systemicity of azoxystrobin, tebuconazole, and phosphorous acid. All systemic treatments translocated at least two leaves above where fungicide was applied in the field, and azoxystrobin and phosphorous acid resulted in greater inhibition seven days after fungicide application compared to earlier samples. In studies of basipetal movement, the first unsprayed leaf below the treated foliage showed a small reduction in lesion development from TPTH at day 4, perhaps from redistribution with moisture, but none thereafter. In contrast, the phosphorous acid greatly reduced lesion development at most sampling dates on both the first and second leaf below the treated foliage for up to 14 days after application. Dormant sprays applied just prior to budbreak were evaluated to reduce inoculum from over wintering lesions, and thus primary infections. Elast most consistently reduced in sporulation from stem lesions, but reductions in disease were relatively small. Other products like chlorothalonil, Sulforix, Lime sulfur, copper, and combinations of these also reduced sporulation in the lab, but had little if any effect on disease development when applied in the field. When applied mid-season after leaves formed but before fruit development, Sulforix and Lime sulfur both sometimes reduced nut scab, but not nearly as much as commercial covers sprays. Results from this study will contribute to managing F. effusum more efficiently with fungicides, especially during the early part of the growing season.