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Contribution of mid-season cover sprays to management of peach brown rot at harvest
N. LALANCETTE (1), J. Gager (1), K. A. McFarland (1). (1) Rutgers University, Bridgeton, NJ, U.S.A.

Protectant fungicides are routinely applied to peach trees during the period from shuck-split through early pre-harvest. These cover sprays are applied to control peach scab, rusty spot, and anthracnose. However, results from fungicide treatments in 2010 and 2012, which lacked the typical pre-harvest applications, indicated that these mid-season sprays may also provide extended residual activity for control of brown rot, caused by <i>Monilinia fructicola</i>. To confirm these observations and determine the mechanism of this control contribution, a field study was conducted during 2012 and 2013 in an experimental peach orchard. Four protectant fungicides (captan, sulfur, ziram, and thiram) were applied from shuck-split through sixth cover. Captan and thiram in 2012 and captan in 2013 significantly reduced brown rot at harvest. Estimation of fungicide levels on fruit, using an in vivo bioassay based on <i>M. fructicola </i>spore germination, showed that residual activity was the primary mechanism for control. Some anti-sporulant activity against blossom blight cankers was also detected, but this form of control was not sustained through the pre-harvest period. These findings indicate that residual activity from mid-season applications of protectant fungicides (<i>i</i>) can contribute significantly to the efficacy of pre-harvest programs and (<i>ii</i>) may play an important role in reducing selection for resistance among site-specific fungicides typically applied during the pre-harvest period.

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