To use the chart, remember that when rain begins after sunset, leaf wetness should be assumed to begin at sunrise. For all other events, times should be computed from the start of rain. However, in low-inoculum orchards, results from research in New York indicate that when rain begins at night, ascospore release, and infection periods, should be presumed to start at dawn. After scab lesions are present, conidia will be available to initiate disease and night time wetting hours will not be eliminated from the wet period calculations. Revised criteria for leaf infection by ascospores of Venturia inaequalis .
Times are minimum hours of continuous leaf wetness required for infection at each temperature.
Fire blight infection risk is moderate through the remainder of the week due to average daily temperatures below 60 F and epiphytic bacteria populations below threshold, according to the Maryblyt model. Infection risk increases later in the week as average daily temperatures reach 60 and bacterial populations approach the threshold. Remember, risk can increase quickly with higher than predicted temperatures. For best blossom blight control, apply Streptomycin just before an anticipated infection. Re-apply in 4 days if high risk conditions persist.