Virginia Grape Disease Updates

  In preparation for hurricane Ida, here is some information that you may find useful (This is a repeat of the previous post, but I received some emails asking for them.) 1)  List of short PHI fungicides for late-season diseases (will open a pdf file) 2)  Updated presentation from the last virtual field day (will open a pdf file). Recent downy mildew risks Many of us have been experiencing more rains lately than the past several months, here are a number of days with downy mildew risk events in the past two weeks based on the NEWA’s DMCast. Many of these rains have been sporadic in terms of area and time it covered, so, use these numbers as a guide. Bristol: 14 days (latest was on 8/30) Floyd: 9 days (latest was on 8/29) Charles City: 14 days (latest was on 8/30) Tyro: 7 days (latest was on 8/30) Red Hill: 5 days (latest was on 8/29) Washington: 8 days (latest was on 8/29) Winchester: 9 days(latest was on 8/29) It is probably a good idea to protect your vines against down...

I mistakingly placed Vivando, which does not work on downy mildew, on the downy mildew table. Please strike it out or use the updated version below. 1)  List of short PHI fungicides for late-season diseases (will open a pdf file) 2)  Updated presentation from the last virtual field day (will open a pdf file).

Presentation slides Thank you to those of you who were able to make it to the meeting today. Here are slides from today's presentation (open PDF).  Up-coming meetings Eastern Section American Society for Enology and Viticulture annual meeting (7 – 8 July): The ASEV/ES meeting will occur on-line this summer. See https://www.asev-es.org/ for details on the meeting, which will include research presentations and a panel discussion entitled “Future Grape Cultivars for Eastern North American Growers”. Eastern Viticulture and Enology Forum (13 July): The July 13th meeting is the next of a series of 4 virtual meetings organized by viticulture and enology extension specialists at Penn State, Cornell, and Virginia Tech. In addition to regional round-ups of seasonal progress, specialists from around the eastern US address pre-submitted questions from participants. Registration instructions and additional information about the meetings can be found on the attached Word document. Virginia Viney...

It looks like we all received much-needed rains, which is good for vine growth. However, since most of our vines are still within the critical period for cluster infection by downy mildew, powdery mildew, and black rot (~ until 6 weeks after bloom for V. vinifera , ~ 4 weeks for V. labrusca ), it also means that we may have had risk events for disease infection. Since the month of May was dry, I think the overall disease risk is low for downy, black rot, and other diseases that are driven by rain (e.g., ripe rot and Botrytis), but I just want to go over recent NEWA outputs.  Disease risks from the recent rain events Westfield (Close to Bristol, VA) It seems that the southwest VA received quite a bit of rain over the past two weeks! I would think many cultivars are close to the end of the critical period, but if you are concerned, a DMI fungicide and a Ridomil or Phos-acid product are effective for black rot and downy mildew, respectively. These materials can be applied a few days a...

Updated: Links below are for the 2021 edition of Pest Management Guides. The first one is for home gardens, and the second is for commercial productions. I asked them to provide by chapter (= crop) and they made changes. :) 1) Visit the page by clicking one of the links below. (It is rather a slow page. Please be patient.) 2) Scroll down until you see "Links to individual chapters." Grapes are chapter 3 for both Home (Home Fruits) and Commercial Crops (Grapes) 3) Once you get to the site, click "PDF", then "Preview", and it will open a new window.  4) Scroll down a bit, and click "Download Version" to download the file to your computer.  2021 Home Grounds  Pest   Management   Guide 2021 Horticulture and Forest  Pest   Management   Guide

Here are links to the 2021 edition of Pest Management Guides. Unlike the past years, all the crops are combined together. (i.e., I cannot separate the grape section.) Once you get to the site, click "PDF", then "Preview", and it will open a new window. Then you need to click "Download Version" to download the file to your computer. Once the document is downloaded, you can search the document to find "grapes". 2021 Home Grounds  Pest   Management   Guide 2021 Horticulture and Forest  Pest   Management   Guide

It was very nice to see you all at the meeting. Here's the content of my handout. Seasonal grape disease updates For VVA Summer Technical Meeting at Stone Tower Winery 12 June 2019 Mizuho Nita nita24@vt.edu Grapepathology.blogspot.com The critical period for cluster infection: Grape clusters are sensitive to infection by powdery mildew, downy mildew, and black rot from the time of bloom to 4-6 weeks after bloom. The length of this critical time depends on the cultivar, 3-4 weeks for American grapes (V. labrusca),  5-6 weeks for French grapes (V. vinifera), and somewhere between the two for hybrids. Please make sure that you have good coverage during the critical period. In a typical year, once we pass the Fourth of July weekend with a clean canopy, we can relax a bit. We are a week or two ahead of “normal” year, so, you may able to relax sooner this year. Downy mildew: Rainfall is not as intensive as the last year (knock on the woods!), but there are enough to driv...

Many people in northern VA are about to see blooms in a few weeks, and I am sure the rest of the regions are about to see bloom very soon.  Bloom is a start of the critical time for cluster infections by downy mildew, powdery mildew, and black rot. Bloom time is also the critical period to prevent Botrytis, ripe rot, and bitter rot, because pathogens of these diseases can infect flower parts and develop symptoms later. What I recommend often is the use of protectant materials to protect tissues for 4-6 weeks for V. vinifera varieties, and 3-4 weeks for V. labrusca varieties, which should translate into 3-4 sprays for V. vinifera , and 2-3 sprays for V. labrusca .  If you have hybrids, they are somewhere in between, so, 4-5 weeks to be protected.  As usual, please make sure to rotate mode of action (= FRAC) groups. Since we have experienced rain every weekend (and looks like another rainy weekend coming up), we need to be on top of downy mildew and black rot manageme...

It has been another rainy weekend (1.5 inches so far and still counting), and looks like next weekend will be wet again... Hopefully, this year won't as wet as the 2018 season... Hopefully, you can provide good protection before the rain, but even if you did, rain more than 1-2 inches can wash the material away from the canopy. Dr. Annemiek Schilder at Michigan State University has a great article about rain and wash off of fungicide . Her work suggests that although only a 0.04 inch of rain can wash a certain percentage of a material from the leaf, it takes about 1-2 inches to actually having a negative effect on the efficacy since the rate you apply is typically much higher than the threshold for the efficacy of the material. Downy mildew symptoms on the upper leaf surface When we have the next chance of application, what material(s) should we apply? I think many of us are about 2-4 weeks away from the bloom, so, the major concern is downy mildew. If you think you have mi...

Here's a 2019 version of fungicide application template. Please read the footnote for downloading onto your computer or copy to your Google Drive to use it. This template is designed to be used as a guide. You need to create your own plan based on your vineyard(s)!! If you have time tomorrow afternoon, please join us for our first grapeIPM.org training session , which will be held at Horton Vineyards from 1 PM. It would be a great excuse to visit Horton to taste their award-winning wines!

Many of you are about to be done with harvest and some may still have a few more weeks to finish this rainy season. This is a reminder for disease management after harvest. The main reason for you to keep your vines clean after harvest is for winter preparation. Grapevines need to store carbohydrate to survive the cold temperature during the winter. If there is not enough foliage on the vine, it may increase the risk of winter injury. The main target diseases are downy mildew and maybe powdery mildew. I do not typically worry about powdery mildew at this late in the season, unless you already have an on-going outbreak that started a few months ago. Downy mildew is common after late-August in our area and severe infection can result in defoliation. Therefore, in a typical year, downy mildew is the one that I would like to control after harvest. Since it will be after harvest spray, you do not need to worry about the PHI (pre-harvest interval). Thus, you can apply a combination o...

I received several emails and phone calls concerning spray before the upcoming hurricane Florence. Hopefully, we will have a window of opportunity to apply materials. Looks like we have a break from rain starting tomorrow for maybe 1.5 to 2 days. Here is the list of materials with low PHI (same as the one I posted last month). Just FYI: here are previous posts about... Late season downy management Botrytis gray mold management Once you have about 1.5-2 hours for the materials to dry after application, that will be sufficient for them to stick to the leaf and cluster surface. Good luck!!

At Winchester, the night time relative humidity has been still very high, close to 100%, in nearly every nights in the past three weeks. In addition, we have been observing rapid development of thunderstorms, pretty much every day in the past few days. I know I sound like a broken record, but these conditions favor downy mildew development because downy mildew pathogen prefers to produce spores under dark, humid conditions. Then spores will be spread via rain. At this point, you do not need to worry about downy mildew infection on clusters; however, they can still infect leaves. Often time, you will initially see infection on the top of the canopy because younger leaves are more susceptible than older ones. Losing the top leaves and laterals are not a big deal; however, once the infection gets severe, it can defoliate many leaves rather quickly (as in the picture above), and that can affect maturing process. Knowing how wet this year has been, it is probably wise to be proactive ...

Powdery mildew colonies at the center of two leaves in the picture With this wet season, what we think most are downy mildew, black rot, Phomopsis, and Botrytis. Powdery mildew is often associated with a dry season, partially because this pathogen does not require rain for its infection process. However, what they also like to do is grow on shaded leave because they are sensitive to the UV radiation. With very clouded canopy from strong growth triggered from heavy water input (= rain), there are lots of leaves shaded by other leaves. Well, at least that is true in my vineyards... Sure enough, when I took a look at these leaves, I found powdery mildew colonies.  You can see a small white fuzz (= powdery mildew colony) on two leaves in the picture above. Note that how the leaves are shaded. We have a fair number of options for powdery mildew management. Sulfur (FRAC = M2) is an economical option, and there are range of products with different modes of action (= F...

Although our bud break was about two weeks behind of a typical year, the wet and hot May pushed our vines forward rather quickly.  Many people in northern VA are about to see blooms (our 3-year old young Chardonnay vines are trace bloom), and I am sure rest of regions are going through bloom by now. This means that many of us are in the critical time for cluster infections by downy mildew, powdery mildew, and black rot. Bloom time is also the critical period to prevent Botrytis, ripe rot, and bitter rot, because pathogens of these diseases can infect flower parts and develop symptoms later. With all the rains we observed, many people are concerned about downy mildew and black rot. In our vineyards, I did not see much sign of downy, but there are many leaves with black rot. It is probably because we did not have major downy mildew outbreaks in past three years. We do have materials with kick-back activities against downy (Ridomil products (FRAC=4), phosphite (FRAC=33, Pro...

As if almost a week of thunderstorms and rains was not enough, it looks like we are expecting even more rain in the coming week. Hopefully, you had a good protection before the rain, but even if you did, rain more than 1-2 inches can wash the material away from the canopy. Please see the article from Dr. Annemiek Schilder about rain and wash off of fungicide . Her work suggests that although only a 0.04 inch of rain can wash a certain percentage of a material from the leaf, it takes about 1-2 inches to actually having a negative effect on the efficacy since the rate you apply is typically much higher than the threshold for the efficacy of the material. When we have the next chance of application, what material(s) should we apply? I think many of us are about 2-4 weeks away from the bloom, so, the major concern is downy mildew. If you think you have missed the window (i.e., there were more than 2 inches of rain from the last application of a fungicide against downy mildew, or it has...

Looks like we will likely to have another round of rain from Hurricane Irma sometimes next week. Just a reminder that we do not have any curative materials for Botrytis and other late season rots. In order to obtain better results, you need to protect your vines before the rain! Please see the previous post for disease management tips and the list of low PHI materials for each diseases. Also, it is very important to keep FRAC codes rotated!

In a typical year, the fourth of July weekend is the time the critical period for cluster infection by downy mildew, powdery mildew, and black rot will end for many of us because it will be about 5-6 weeks after bloom. (Bloom this year was about 1-2 weeks ahead of typical years, so, this week maybe it for 2017.)  This critical time varies by varieties, but in general, 4 to 6 weeks and 3 to 4 weeks from bloom for V. vinifera and V. labrusca species, respectively.  After this critical period, you should be able to relax a bit because these pathogens are no longer able to cause disease on berries. Plus, powdery mildew tends to slow down because it is not very active under hot condition (> 90F). So, what’s next?  As usual, disease dynamics depends on environmental conditions, cultivars, and cultural practices you employ, but in general, this is the moment when you will be thinking about late season diseases such as Botrytis, ripe rot...

As of today, it is about 10% bloom at our Chardonnay plots. Since bud break was about 2 weeks ahead of a typical year, things are moving along as we would expect. Of course, bloom in VA almost always has to happen in rain... As for bloom time disease management consideration, please refer to the previous post. From this point on, 4 to 5 weeks will be a critical period for management of downy mildew, powdery mildew, and black rot. Please make sure to keep your vines covered. Once again, providing a protection is much better and easier than playing a catch-up, especially if it comes to grape disease management in VA. You can use protective materials such as mancozeb, copper, and sulfur as your backbone, and add more specific (and often locally systemic) materials. Some of these materials have efficacy against multiple diseases (either by itself or through the combination of two materials). Examples are DMI, aka SI (FRAC = 3), e.g., Rally, tebuconazole, Mettle, etc. Inspir...

Some shoots of our vines are about to reach the second catch wire, but I saw many that were still about 10-12 inches too. It looks like series of rain during the month of April drove developments of black rot and Phomopsis. Although it was not severe, I found several vines with leaf lesions of black rot, and a few vines with Phomopsis. Tan-colored lesions are symptoms of black rot. If you click the image, it will open a larger file where you can observe fruiting bodies (tiny black specks) within these lesions. It is a bit difficult to see, but, please note the holes on the upper picture (in the blue circled area). The lower picture shows more characteristic leaf spots of Phomopsis cane and leaf spot. For management tips, please refer to my  around bloom disease management consideration post.  Please remember that clusters will be susceptible to black rot from bloom to 4-5 weeks after bloom. Looks like Winchester area is expecting chances of rain on Friday, M...