Evaluation of phosphite to control scab on pecan in the southeastern U.S.A.
C. H. BOCK (1), T. B. Brenneman (2), M. W. Hotchkiss (1), B. W. Wood (1)
(1) USDA-ARS-SEFTNRL, Byron, GA, U.S.A.; (2) University of Georgia, Tifton, GA, U.S.A.
Phytopathology 101:S17

Pecan scab (caused by Fusicladium effusum) infects pecan and severe disease can cause yield loss. The efficacy of phosphite, an elicitor of systemic acquired resistance (SAR) was evaluated in field experiments in 2009 and 2010. Biweekly applications of phosphite (Prophyt at 2.64 L 1000 L^–1 ha^–1) were compared to an industry standard fungicide, triphenyltin hydroxide (TPTH, Super-tin at 0.90 L 1000 L^–1 ha^–1). Both phosphite and TPTH reduced scab provided equally good control of leaf scab, with the exception of one of the TPTH treatments in 2010. Phosphite and TPTH also gave equally good control of scab early in fruit development (Jul/Aug); however, by the final assessment (Sep/Oct), fruit scab severity on phosphite treated trees was greater than those receiving TPTH and in 2010, scab severity was equivalent to the untreated control. There was no difference in fruit volume between phosphite and TPTH-treated plots in 2009, and no difference in nut volume between treatments in 2010, although there were treatment differences in kernel weight and fruit weight in 2010. Results indicate that phosphite provides useful control of pecan scab on both foliage and fruit early in the growing season, but does not provide as good prolonged late-season protection compared to an industry standard, TPTH.