Virginia Grape Disease Updates

 I created a short video describing current projects in my program. 

Hurricane Delta seems to impact our regions, starting Saturday (10/10), and rain may last until Tuesday (10/13) or so . Depends on your location and cultivar selection, you may have some grapes that may need more time before harvest. ( A link to Hurricane Delta tracker from Weather.com - will play a video. ) The target diseases right now are late-season fruit rots (Botrytis, ripe rot, bitter rot, etc.) and downy mildew (on leaves). The links here are  the presentation slides from the last viticulture meeting that covers some of the diseases mentioned above  and   a list of short PHI materials for Botrytis, powdery mildew, and downy mildew , which may help you decide what to do. If you decided to wait until the storm is over, there are several materials with a very short PHI that you may want to consider, such as Oso/Ph-D or Elevate for Botrytis and a phosphorous acid (Prohyt, Phostol, etc.) or Lifeguard for downy mildew. FYI: when we tested in the field, Oso plus Double N...

Looks like a tropical storm Marco is moving westward, but Laura may hit our areas during this weekend. The current forecast shows (opens a new window with a link to Weather.com) potential movement to Virginia and surrounding states around this Saturday (8/29). Many white cultivars will be either ready to pick or getting very close to harvest, and red cultivars may have several weeks to go, depends on where you are what you grow. At this point in the season, the target diseases are late-season fruit rots (Botrytis, ripe rot, bitter rot, etc.) and downy mildew (on leaves). For whites, it may be a decision of when to pick, but not what to spray. If you decided to wait until the storm is over, there are several materials with a very short PHI that you may want to consider, such as Oso/Ph-D or Elevate for Botrytis and a phos acid for downy mildew. FYI: when we tested in the field, Oso plus Double Nickel combination worked well against sour rot. For reds, it will depend on when and what you ...

With recent rain events and warm and humid nights, the risk of downy mildew and Botrytis are probably high in many areas of Virginia. For example, I counted seven days (at Winchester, VA) and eleven days (at Rustburg and Scottsville, VA), with downy mildew infection events in the past two weeks according to the NEWA model ( http://newa.cornell.edu/ ). It is very important to keep your vines protected, and if you think you need to have a kick-back activity against downy mildew to counteract the recent rain event that your previous spray might not have provided good coverage, add a phosphorous acid material such as Prophyt or Phostrol.  Please refer to this list of materials with short PHI since some of the cultivars are getting very close to harvest. Note: although both sulfur and copper have a short PHI, we typically do not recommend spraying these materials within 3-4 weeks of harvest due to its potential negative impacts on the fermentation or wine quality.  When some ...

Thanks for attending today's online Extension meeting. Please find the materials I discussed today below. 1) Presentation slides (will open a new window with a pdf file). 2) List of short PHI materials for Botrytis, powdery mildew, and downy mildew.

Central and northern VA received much-needed rains in the past two days. Looks like the chance of thunderstorm is high in today and tomorrow too. Several people asked me whether they need to jump on their tractor now and spray for downy mildew or not. Here are snapshots of downy mildew risk events in three locations during the past two weeks. Southwestern VA, Floyd: none Central VA, Afton: 7/11, 7/22, and 7/23 Northern VA, Winchester, 7/11 (a very short one) and 7/22 Since we have been experiencing a very dry season, I do not think we need to react to every rain event, especially if your previous spray was less than 7-10 days ago . If you are due to spray soon anyway, it may be a good idea to have a Phos acid material (e.g., Prophyt, Phostrol, Agri-Fos, etc.) in the tank-mix as insurance. For example, my previous spray (a fixed copper material) was on the 11th and my plan is to spray my vines this Saturday (the 25th) with a Phos acid, sulfur, and another PM material (Vivando,...

Here are snapshots from the NEWA risk models from the past two weeks. Floyd: no black rot or downy mildew infection events Afton: black rot and downy mildew infection event on 7/1-2. Winchester: downy mildew infection event on 7/8 Looks like we are having relatively dry conditions. Depends on where you are and which cultivar you grow, you may not need to worry too much about downy mildew or black rot for a while. Also, most of our vines are done with the critical period of cluster susceptibility to black rot, downy mildew, and powdery mildew. What I would keep eye on will be powder mildew, since the pathogen does not require water for infection. Sulfur is a good material, and you can add powdery mildew materials, such as Quitec, Vivando, Torino, DMI, and SDHI to provide extra protection. When you spray a sulfur product, make sure the sprayed material will be dried up before temperature gets above mid-90F. If the leaf surface is wet with sulfur when the temperature gets high, it ...