Submitted to: Crop Protection Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/17/2012
Publication Date: 4/15/2012
Citation: Bock, C.H., Brenneman, T.B., Hotchkiss, M.W., Wood, B.W. 2012. Evaluation of a phosphite fungicide to control pecan scab in the southeastern USA. Crop Protection Journal. 34:58-65.
Interpretive Summary: Pecan scab (caused by Fusicladium effusum) infects pecan and severe disease can cause yield loss. The efficacy of phosphite was evaluated in field experiments in 2009 and 2010. Biweekly applications of phosphite were compared to an industry standard fungicide, triphenyltin hydroxide. 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), but fruit scab severity on phosphite treated trees later in the season was greater than those receiving TPTH. In in-vitro tests, phosphite was directly toxic to pecan scab at concentrations similar to those applied in vivo. 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.
Technical Abstract: The efficacy of phosphite, a potential elicitor of systemically acquired resistance (SAR) is compared to the protectant fungicide triphenyltin hydroxide (TPTH) to control pecan scab caused by Fusicladium effusum. Efficacy is evaluated in four field experiments involving biweekly foliar applications of both fungicides to trees of five susceptible cultivars of pecan (Carya illinoinensis) and assessment of disease severity on foliage and fruit. Both phosphite and TPTH reduced scab severity on foliage equally well compared to the untreated control, with the exception of one of the TPTH treatments in 2010. Both phosphite and TPTH provided equally good control of disease early in fruit development (Jul/Aug); however, by the final assessment (Sep/Oct), scab severity on phosphite treated trees was most often greater than those receiving TPTH and in 2010, severity was equivalent to the untreated control. Despite a suggested lack of late-season protection with phosphite there was no difference in fruit volume between phosphite and TPTH-treated plots in 2009, and no difference in nut volume in 2010, although there were treatment differences in kernel weight and fruit weight in 2010. Regression analysis demonstrated the effect of scab on yield loss and confirmed the value of scab control on susceptible cultivars. In-vitro tests showed that phosphite is toxic to scab in-vitro at rates applied in the field; thus, implying direct fungitoxicity. Results indicate that phosphite provides useful control of pecan scab on both foliage and fruit early in the growing season, but might not provide prolonged late-season protection compared to an industry standard (i.e., TPTH).