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Refinement of peach cover spray programs for sustainable management of brown rot

Norman Lalancette: Rutgers University

<div>Brown rot is typically controlled with site-specific fungicides applied during the preharvest period. This practice has resulted in development of fungicide resistant <em>Monilinia fructicola</em>, the causal agent of brown rot. However, recent research has shown that the protectant fungicide captan applied during the prior cover spray period can contribute 50 to 69% control of rot at harvest, thereby reducing the size of the <em>M. fructicola</em> population exposed to the site-specific materials. Thus, the objectives of this study were to determine the minimum rate and optimum timing of captan cover sprays that still contribute effectively to brown rot control. Results showed that control with captan was rate dependent, with 51, 69, and 78% control observed at 2.24, 2.80, and 3.36 kg/ha, respectively. Treatment timings indicated that the final two cover sprays yielded control equivalent to the full season seven-spray program. Estimation of fungicide levels on fruit, using an <em>in vivo</em> bioassay, showed that residual activity was the primary mechanism for control. As hypothesized, mid-season cover sprays were ineffective. However, 40% control exerted by the three earliest cover sprays indicated that significant quiescent infections may be occurring on green fruit. These findings show that multi-site protectant fungicides applied during late cover sprays can contribute significantly to brown rot management. Additional data are needed on the significance of quiescent infections.</div>