Disease risks from yesterday's rain

At Winchester, the second set of rain started at 4:00 pm on 5/12/10 and then we had several short showers during the night. In the end, the relative humidity was high (>90%) until 11:00 am on 5/13/10. The average temperature was 64F, starting with higher temperature (72F) and ended lower (55F). The total amount of precipitation was 0.08 in.

Thus, we had about 18 hours of wet event. The temperature during 12th was close to the optimal temperature for downy mildew. As I mentioned in the previous post, we (Winchester) had a potential event for downy on May 3rd, so, I think this rain gave the fungus a good opportunity. Also, it was high risk event for black rot and Phomopsis.

We are expecting to have more rain events during the next week throughout VA. Plus, I think most of us are expecting bloom very soon. The period between bloom to 4-5 weeks after bloom is the critical time for berry infection by downy mildew, black rot, and powdery mildew. It is unfortunate that rain is coming at the bad moment, but please stay on top of it. Please check your local weather closely. We can relax the spray schedule, once the critical period is passed.

Comments

Downy mildew gallery

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

Season's Greetings!

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Recent downy mildew risk events

It seems that several rain events have happened over the course of the past two weeks or so. Here is a summary of recent downy mildew risk events, based on the NEWA stations and DMCast. Bristol, VA Fifteen days with potential DM infection event(s) since Sept 1. The latest event happened last Sunday. Floyd, VA Eleven days with potential DM infection event(s) since Sept 1. The last event happened last Friday. Charles City, VA Twelve days with potential DM infection event(s) since Sept 1. The latest event happened yesterday. Central VA Since there was a wide variation among stations, I am listing several around Central VA. Tyro, VA Nine days with potential DM infection event(s) since Sept 1. The latest event happened yesterday. Red Hill and Crozet, VA Only one day with potential DM infection event(s) since Sept 1. Olympic Lake Thirteen days with potential DM infection event(s) since Sept 1. The latest event happened last Sunday. Washington, VA Eight days with potential DM infection event

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