Susceptibility of Immature and Mature Sweet and Sour Cherries to Monilinia fructicola

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Abstract
Fruits of Vista and Bing sweet cherries [Prunus avium] and Montmorency sour cherry [P. cerasus] were harvested at weekly intervals between shuck fall and full maturity in 1986 and 1987. Unwounded fruits were inoculated individually with a 30-.mu.l drop containing 106, 105, 104, or 103 conidia of Monilinia fructicola per milliliter. Fruits were evaluated for lesion development after incubation for 6 days at 20 C and relative humidity above 95%. Sweet cherries were more susceptible to infection than sour cherries at intermediate and low inoculum concentrations. Initially the immature fruits of both species were as highly susceptible to infection as mature fruits at inoculum concentrations of 106 conidia/ml. Host resistance rose with the onset of pit hardening but decreased 3 wk before maturity, coinciding with yellowing and reddening of the epidermal tissue. Fungicide protection against brown rot appears warranted at shuck fall and before harvest for both sweet and sour cherries. Midseason protection appears necessary for sweet cherries but not for Montmorency sour cherry.