Disease risks from weekend's rain

Finally! Winchester area had decent rain events over the weekend. The rain event started from 7:40PM on Thursday (we missed the one earlier that day, although other northern VA area received thunderstorms), and a series of rain went pass throughout last Friday. The relative humidity was above 90% until 8:20PM on Friday. It resulted in almost 25 hours of wet event with an average temperature of ~74F. It was a long and warm enough for downy mildew and Botrytis. Then we had several rain events on Saturday and Sunday. None of them are very long, but long enough for downy mildew to cause infection.

Once again, we had a dry summer and the threat from downy mildew may or may not be the primary concern. But if you still have a few more weeks to go until the harvest, please keep your eyes on younger foliages (typically you find them on the upper part of the canopy) for the sign of downy mildew. It can go from a trace level to an outbreak in a short time, and heavy infection can cause defoliation on leaves. If you knew you have some downy prior to this series of rain over the weekend and your leaves are not protected, you may want to consider Phosphorous acid products such as Prophyt which should give you a good curative and protective activity against downy mildew (+ short PHI).

Also, there are chances of rain (30-70%) on this Wednesday and Thursday.

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!

I hope you and your family have a good holiday season and a Happy (and safe) New Year! Thanks again for your support of our programs. Here are some recent media highlights. 😉 The link will open a new window. AHS AREC promotional video that highlights some of our activities. The link did not work... It asks you to log in to VT. I will request the IT people to change the setting, but in a meantime, here's the same video. We also appeared in the Library of Congress project “Winery Workers of Virginia”. One more announcement: I will be moving this blog to a new location ( ext.grapepathology.org ) early next year. I had to make a change due to the email subscription service, which has been terminated. You do not need to change your bookmark or your email subscription. The URL will be forwarded to a new site and your email subscription has been moved to a new site already.

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

Virginia Grape Disease Updates

Search This Blog