Evaluation and comparison of phosphorous acid Biofungicides and fertilizer on control of pecan scab

The ‘Desirable’ pecan (Carya illinoinensis) cultivar grafted onto native seedling pecan rootstock in Red River Parish, and the ‘Candy’ pecan cultivar grafted onto ‘Stuart’ rootstock in Pointe Coupee Parish were used to compare the efficacy of foliar applications of Fosphite®, Rampart®, Phostrol® and Nutri-phite® phosphorous acid products on pecan scab (Fusicladium effusum G. Winter) to a standard rotation of commonly used commercial fungicides, and to determine if soil applications of Fosphite®, Rampart®, Phostrol® and Nutri-phite® provide any protection against pecan scab infection in 2011-2012. Pecan scab is the most important disease on pecans in Louisiana in terms of crop loss and money spent on control. Phosphorous acid is easily absorbed by plants and translocated via the xylem and phloem. While most pecan fungicides are applied foliarly, the systemic movement of phosphites can occur following soil applications. If soil applications of phosphites can successfully provide scab protection, then homeowners and commercial growers who cannot afford expensive spray equipment could improve their nut quality, production, and income. Drought conditions in 2011 reduced the incidence of pecan scab in 2011, but there was heavy scab pressure in 2012. Disease prevalence was much greater in trees receiving soil applications of phosphite fungicides compared to trees receiving foliar applications. Foliar applications of phosphite fungicides provided good control of pecan scab and should be considered for inclusion in commercial fungicide rotations. Soil applications of phosphite fungicides did not provide adequate protection against pecan scab at the chemical rates used in the current study. The data for ‘Candy’ and ‘Desirable’ suggests that soil applied phosphorous acid may provide some protection in low scab pressure situations, but had widespread infections similar to control trees when the scab pressure was severe.