Rains forecasted for this weekend.

It seems that we will have a rainy weekend. Chances of rain are around 40-60% throughout the state. Forecasted temperature during the hours with a high chance of rain is around mid-50's to low-60's. This may become our first real risk of disease development. (Of course, since I stated that, we may not get rains.)

If you have sprayed in preparation to the previous rains (i.e, within 10 days or so), then your vines are probably protected. It also depends on how much your vines have been grown and how much rainfall you have received. At Winchester, many of the rain events were showers with less than 0.02 inches of precipitation, and due to more like a normal weather, shoots were not growing as vigorously as they did few weeks ago. Please check your record, vines, and local weather history.

However, if you were waiting until now and your vines are grown considerably, then you may want to protect your vines, simply because there are three days of rain forecasted and temperature range could be high. You can always wait until tomorrow or even Saturday morning to make a decision, but I just want to give you a heads-up. The target diseases are Phomopsis and black rot, and maybe downy mildew. Mancozeb products will provide a good to excellent protection against these diseases. If you prefer using other materials, make sure that the product has an efficacy against all three. I think it is still too early in the season to talk about powdery mildew, but adding a low rate of sulfur is always a good (and cheap) insurance. For rates and list of materials, please refer to PMG or my spray guide that you can find in the links on the right.

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

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