Factors affecting flower infection and disease severity of lowbush blueberry by Botrytis cinerea

Infection of lowbush blueberry (Vaccinium angustifolium Ait. and V. myrtilloides Michx.) flowers by Botrytis cinerea Pers.:Fr. and subsequent disease was determined for differing stages of flower bud development, temperature, and duration of postinoculation wet periods. Conidium germination of B. cinerea at 20 degreesC was poor on immature flower buds when the corolla was beginning to protrude from the calyx (floral stage 174) and when the corolla was half developed (F5), but better when flowers were at the pink bud prebloom stage (F6) or fully open (F7). Infection incidence followed a similar trend; there was none on the F4 flowers, slightly more on F5 flowers, and an increase to over 45 and 98% on F6 and F7 flowers, respectively. Immature green berries were resistant to infection, but nonpollinated ovaries from which corollas had abscised were susceptible to infection. At 4, 8, 12, 16, and 20 degreesC, low levels of infection occurred on F7 flowers after 24, 13, 10, 8, or 6 h of postinoculation wetness, respectively. The infection incidence increased progressively with temperature and wetness duration. Lesions spread from the corolla to the peduncle of flower clusters over a 96-h wet period at 16, 20, and 24 degreesC, but the disease failed to spread beyond the corolla at 4, 8, and 12 degreesC. When flower clusters were inoculated with 10(5) or 10(6) conidia/mL at 20degreesC and incubated over a 96-h wet period, lesions spread from the corolla to the peduncle, but when the inoculum concentration was 10(3) or 10(4) conidia/mL, they did not extend beyond the corolla. These results could help to reduce fungicide applications when disease management programs are based on monitored weather conditions.