Irene stayed little longer than I expected in our area. At the end of Sunday, Winchester area received a total of about 0.5 inches of rain. I was monitoring the RH for last 2-3 days, but it was below 90% (actually it was 60-70% in most of time between rains). It was probably because of high wind due to Irene. Based on this information, the risk of Botrytis is not high; however, as with any precipitation events, it varies dramatically even between short distances. (For example, our AREC station received 1.2 inches or so from Irene.) Thus, please check your local weather service.
At Winchester, we had light rain events during the night of 6/12/09, but it was short events and the relative humidity was low (80% or so), thus it probably did not promote any infections. However, we are experiencing continuing favorable nights for downy mildew sporulation (average T>55F, high RH (80-100%)) for 10 days now. Yesterday, we conducted a formal disease assessment, and observed first incidence of powdery mildew for this season. We had plenty of infection events in last two months, so it was not surprising. At this point, it is a trace level of infection on untreated vines. Downy mildew was the major disease so far. We had up to 40% incidence on untreated vines. Next runner-up was black rot. It varies vine to vine, but some of vine had 10-15% incidence. Phomopsis was omnipresent as I expected from early May rain falls, but severity was low overall. We will examine diseases again in the near future, and I will update as the season goes. Here is downy mildew ga...
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