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Effects of Fungicides Applied During Bloom on Yield, Yield Components, and Storage Rots of Cranberry. S. N. Jeffers, Department of Plant Pathology, University of Wisconsin, Madison 53706. Plant Dis. 75:244-250. Accepted for publication 6 September 1990. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-0244.

Captafol, chlorothalonil, and mancozeb were applied to the same plots, which were established in commercial cranberry (cv. Searles) beds at two locations in central Wisconsin, for three consecutive years to manage postharvest storage rots of fresh fruit. Applications were initiated progressively earlier each year in relation to bloom (late bloom in 1986, 70% bloom in 1987, and 14% bloom in 1988) and were made three times at 14-day intervals each year. Compared with the untreated control, one or more of the fungicide treatments reduced yield (i.e., marketable berry weight per unit area) in all 3 yr at both locations. Chlorothalonil reduced yield most consistently (63% at location 1 in 1987 and 1988 and 20% at location 2 over all 3 yr). Fruit-set was reduced whenever yield was reduced; other components of yield that were routinely affected by fungicides were the proportion of the upright shoots that produced flowers and the number of flowers produced per flowering shoot. Weights of individual berries and the total number of upright shoots per unit area were not affected by the treatments. Incidence of rot was assessed after berries were stored 3 mo at 2 C. Only captafol consistently reduced the incidence of soft, rotted berries and increased the percentage of berries that was marketable. This increase ranged from 4 to 10% over the 3 yr. Chlorothalonil increased the percentage of marketable berries and decreased storage rots in 1986 only when applications were initiated at late bloom. Mancozeb was ineffective at managing storage rots. The incidence of black rot was not affected by fungicide treatments. From isolations conducted with berries harvested in 1988, Apostrasseria lunata consistently was recovered from berries with black rot symptoms. The four most common fungi recovered from soft, rotted berries were Godronia cassandrae, Penicillium spp., A. lunata, and Coleophoma empetri. Frequently, berries from which no fungus was isolated (i.e., sterile breakdown) occurred at each location (57%) of the berries at location 1 and 10% of the berries at location 2). This research suggests that a thorough investigation of the costs and benefits of fungicides applied for cranberry storage rot disease management in Wisconsin is needed.