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Barrett R. Gruber, Libby R.R. Davies and Patricia S. McManus

Copper-based fungicides are effective for managing cherry leaf spot disease incited by Blumeriella jaapii (Rehm) Arx. However, their application has been associated with bronzing discoloration of tart cherry (Prunus cerasus L.) foliage. This work explored the consequences of foliar applications of a copper-based fungicide for tart cherry fruit quantity and quality. ‘Montmorency’ tart cherry trees were subjected to one of the following fungicide programs in 2007, 2008, and 2009: synthetic fungicides only, synthetic fungicides integrated with a copper-based fungicide, or not sprayed. Each year, the number of fruits per shoot and fruit fresh weight and soluble solids concentration (SSC) were measured three to six times during drupe development. Repeated measures indicated no collection date × fungicide program effect on the mean number of fruits (P ≥ 0.48) and SSC (P ≥ 0.14) in all years or on fresh weight in 2008 and 2009 (P ≥ 0.58). There was a collection date × fungicide program effect (P = 0.02) on mean fresh weight in 2007. On 6 July 2007, trees assigned to the integrated copper program were observed having 23% and 27% lower fruit fresh weights than trees assigned to the nonsprayed and synthetic programs, respectively. However, pairwise comparisons indicated no difference in fresh weight between the integrated copper and the nonsprayed programs (P = 0.26) and no difference between the integrated copper and synthetic programs (P = 0.25) on the final collection date of 2007. In 2007, fresh weight decreased slightly (slope = –0.08, P = 0.05) as leaf bronzing severity increased, whereas SSC increased slightly (slope = 0.31, P = 0.06). In 2008 and 2009, there was no relationship between bronzing severity and fresh weight or SSC (P ≥ 0.34). These results indicate that applied copper does not lead to fewer fruits per shoot or reductions in fresh weight or SSC of mature fruit and that the observed range of leaf bronzing severity had little to no influence on fresh weight and SSC.