First report of blossom blight and green fruit rot of sweet cherry caused by Sclerotinia sclerotiorum in Oregon.

During May and June of 2006, ‘Lapins’ sweet cherry (Prunus avium) trees were observed with white fungal growth on blossoms and young fruit in two commercial orchards in central Oregon (Wasco County). Entire blossom clusters and 30% of fruit clusters were affected. Rot on the fruit was firm, light brown, and covered the entire fruit, extending halfway down the pedicel. Affected blossoms were light brown and stuck to adjacent fruit and blossoms. Six disease samples from fruit, four samples from pedicels, and four samples from blossoms were surface sterilized and plated on potato dextrose agar acidified with lactic acid ([APDA] 1.5%). A white fungus producing sclerotia measuring 4 to 8 mm in diameter was recovered from all the samples after 10 days on APDA at 25°C. Koch's postulates were satisfied by inoculating green, pea-sized ‘Lapins’ cherry fruit with mycelial plugs colonized by the white fungus. Symptoms and signs similar to those seen in the orchard were produced. The same sclerotium-producing fungus w...