Sunday evening, April 27: Weather forecasts for the coming week vary, but at least one of the forecasts is suggesting that we may have more than 3 inches of rain in the Hudson Valley between Tuesday morning and Thursday evening. The apple growth stage in the Hudson Valley and ascospore maturity (based on several different models) are such that unprotected orchards could sustain very severe scab infections if the forecasts are correct.
The dilemma is that many orchards were probably sprayed last Thursday or Friday, but the protection from those sprays has been compromised both by the two-thirds inch of rain that occurred early on Saturday morning and by additional leaf expansion since then. If we receive more than an inch of rain between Tuesday and Thursday, then trees sprayed prior to Saturday morning (26 April) will likely run out of protection before the wetting period ends. Those using a protectant fungicide program will want to have a fresh cover of mancozeb plus captan in place before the rains begin on Tuesday whereas others may opt for one of the protectant fungicides (captan or mancozeb) plus one of the fungicides that is absorbed into leaf tissue: Flint, Sovran, Fontelis, Merivon, Luna Tranquility, or Inspire Super. Those who cannot re-apply fungicides to all of their acreage before rains begin on Tuesday should focus on recovering their most scab susceptible cultivars and/or blocks known to have higher levels of inoculum from last year.
Although some of the NEWA stations suggested that we had a scab infection period over the weekend, I suspect that risks from that potential infection period were rather low, especially where the rain started after dark on Friday night. At this time of year few ascospores will be released at night, and the wetting periods of the weekend were generally too brief and cold to add up to an infection period if night time hours are omitted where events began after dark.