Virginia Grape Disease Updates

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!!

Field day: Use of Protective Covers to Reduce Fungicide Usages in (Organic) Wine Grape Production in Virginia 5 September 2018 1 – 4 pm AHS AREC 595 Laurel Grove Rd. Winchester VA 22602 Mizuho Nita, Ph.D, Virginia Tech Nita24@vt.edu The total acreage of certified organic grape production in the US has increased from 12,575 acres in 1995 to 38,664 acres in 2011. However, only three Virginia vineyards have been approved by the USDA for their organic management practices for wine grape production, and only two have a winery as of 2018. The main reason why organic wine grape production is not common in VA or any other states located the east of Rockies is fungal diseases, which are driven by frequent rain events during summer months. Thus, the Nita lab has established two experimental vineyards with financial aid from the USDA/NIFA VDACS Specialty Crop Research Initiative Block Grant in 2012. Although we identified several cultivars that may do well with the orga...

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 ...

In the last several days, the nighttime relative humidity has been very high (>90%) and temperature has been in the upper 60s ~ lower 70s. This condition is favoring spore production of downy mildew. Please check my previous post about downy mildew management.

Just a reminder on downy mildew management: although the month of July was dry until this week, many of us had a very wet early summer that fostered downy mildew development. In addition, during the last several days, the night time temperature was in low 70s and RH was 95-99%, which was an ideal condition for downy mildew spore production. Thus, if you have not, make sure to protect your vines against downy mildew when you have a chance. If you think you have missed the window, we still have some options. We have materials with kick-back activities against downy (Ridomil products (FRAC=4), phosphite (FRAC=P7, Prophyt, Phostrol, etc.). One of two Ridomil product (Gold MZ) has a mancozeb, which has a 66-day PHI, so, unless you have a late season red, you probably need to use the other formulation, which is Ridomil + copper. Both Ridomil and phosphite are good with kick-back, but you probably want to add a protective material to cover both directions. Examples would be captan (...

Thanks again for coming to today's vineyard meeting. I learned quite a bit! Here are my handouts (sorry for not bringing enough today!!) 1) Sprayer calibration handout  (will open a PDF file) 2) Sprayer calibration aid (spreadsheet) (In order to use it, please download onto your computer [File -> Download as...]) 3) Seasonal grape disease reminder  (will open a PDF file)

Most of us are about to finish the critical time when clusters are susceptible to infection by downy mildew, powdery mildew, and black rot.   This critical time varies by varieties, but in general, 4 to 6 weeks and 3-4 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 no longer able to cause disease on berries. So, what’s next?   As usual, disease dynamics really depends on environmental conditions, cultivars grown, and cultural practice, but in general, this is the moment when you will be thinking about late-season diseases such as Botrytis, ripe rot, bitter rot, and sour rot.   The spray timings for Botrytis is at bloom, bunch closure, and veraison.   The pathogen seems to be active throughout the season. The main reason we recommend the application of a Botrytis specific material at bunch closure is that this most likely to be the last...

Here are my presentation materials from recent meetings. It will open a new window with a PDF file. 1) Slides from beginner's workshop on 6 June 2018. 2) Handout from the VVA summer technical meeting on 12 June 2018

There will be a meeting in the 23rd of June (Sat) at Rivah Vineyards at The Grove, Kinsale, Virginia. The meeting starts at 6:30 PM. If you are in the Northern neck or surrounding area, please join us.

A few people asked me about the specific location for tomorrow's VVA summer technical meeting. The meeting will be held at Brown Bear vineyards (Formally Spring Hills), and the nearest address is: 229 Spring House Lane, Woodstock VA 22664. Tremain prepared a set of screenshots to help you get there. (Click the images to expand) Spring House Lane is off from Alonzaville Rd. Your GPS may overshoot. When you see the vineyard in front of you, you should see the farm road on your right to get to the garage/barn. See you tomorrow!

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...

I have added more information to the yesterday's post. Please check it out. Options against current rainy condition .

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...

Bud break for our younger (2-3 years old) Chardonnay happened around 4/20/2018, and for older Chardonnay, it was the last weekend, (4/27/2018). Looks like we are about 1-2 weeks behind of a "typical" spring. But as with a typical spring, rain comes when grapes break buds! Looks like we will see some precipitations this weekend.  Please make sure to have a good protection against Phomopsis as we discussed in the previous post.   Let's hope that our season will be as good as 2017.

Our Chardonnay and some of the hybrid vines are in bud swell stage as of this week, and others are tagging along.  It looks like we will see bud break very soon with warmer temperature (but next week should be cooler). One of the diseases you need to consider this time of the year is Phomopsis cane and leaf spot.  It causes minor leaf spots, which is more obvious to our eyes, but the more important damage is caused by necrotic lesions on shoots and rachis. It also causes berry rot; however, it is not common with wine grapes because of our spray programs. Materials for black rot and downy mildew are often effective against Phomopsis. Thus, the fungicide coverage for these diseases is also working as management of Phomopsis, especially later in the spring and early summer. Some cultivars, such as Viognier and Seyval Blanc, are more susceptible to Phomopsis than the others. Phomopsis takes a while to establish in the vineyard. It may take 5-6 years for Phomopsis to become ...

Thank you for who attended NJ's "Grape Expectations" meeting two weeks ago. (I think it is a very cool name for an Extension meeting.) Sorry for not able to post my presentation sooner. I have been out for other meetings. Click here for slides from my presentation. It will open a PDF file on Google Drive.

Here are slides from my student's presentations. The link will open a PDF file on Google Drive. Please note that many of data presented here are still preliminary and we are working on publications. 1) Wong and Nita " Evaluation of Rhizobium vitis ARK-1, A Biological Control Agent For Crown Gall of Grapevine, Using R. vitis Isolates From Virginia Vineyards " 2) Oliver and Nita " Laboratory and field fungicide testing for control of Colletotrichum species isolated from Virginia vineyards "

Thank you again for those of you attended one of my sessions. Here are links to my presentations. It will open PDF files on Google Drive. 1) Interactive grape disease management 2) Advanced topic in grape disease management: Fungicide resistance Please note that we will have more meetings coming up: 16 March 2018 Pruning workshop at Breaux Vineyards (Northern Virginia) 17 April 2018 Vineyard IPM workshop at Early Mountain Vineyards (Central Virginia) 6 June 2018 “Beginner’s” Grape Growing workshop Virginia Tech’s AHS Jr. Agricultural Research and Extension Center, Winchester VA We hope to see you there!

The label of Presidio has been changed, and unfortunately, the grape was removed from the list of hosts. This means that we no longer able to purchase Presidio to control grape downy mildew. If you already have it, it is still legally OK to use it for the grape, as long as you keep the original label. (and if you do, please make sure to mix with another mode of action such as mancozeb, captan, copper, since the active ingredient for Presidio is known to have the fungicide resistance issue, and required by the label to mix.)

Here's this year's handout for pruning time disease considerations  (this link opens Google Drive with this year's recommendation for trunk disease management). As I noted in this handout, the first line of defense against trunk diseases that may infect through pruning cut is a cultural control. Make sure to pick dates when you are expecting several days of dry weather. In this handout, I refer to Topsin-M as a choice of trunk disease management, especially for Botryosphaeria canker, which is very common in our area. The product has been transferred to a new company in 2017, and there are changes in the label. [Note: The US distributor is still the same (UPI), thus, I do not think it will affect where you can purchase the product.]  If you are using Topsin-M for pruning wound protection, please update your label.  You can download the new label by clicking this link  (will open Google Drive). If you are pruning, and wondering whether you can protect pruning ...