Winchester area received a series of rain events from 5:30AM on 18 April. It lasted about 10 PM. Since the rain stopped at night, leaf wetness is still on-going (i.e., RH > 90%) as of now (~9AM, makes it 27.5h of estimated leaf wetness), and the average temperature is about 49F. Thus, it has been an infection event for Phomopsis and black rot.
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...
Whats the best thing to spray at this point if you haven't done your first spray yet. Should you still go with Mancozeb?
ReplyDeleteSince none of the materials we have have activity after the infection on Phomopsis, it is probably better to go with mancozeb products.
DeleteWe had a several rain events that are warm enough for black rot, thus I will keep eye on black rot development too. It typically take about 2-3 weeks for black rot to develop symptoms. Once you start seeing black rot, and if you are expecting (or experienced) a warm rain event, then I would recommend to add a DMI to your schedule.
Note: it is probably not worth adding a DMI at this point because in typical year, black rot appears later in the season, exception is the case where you had an outbreak of black rot last year, and know that there are many inoculum available. Even with that, adding a DMI at this early in the season make your season-long spray program (i.e., rotation of mode of action) more difficult. Thus, I would proceed with caution.