Virginia Grape Disease Updates

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...

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!

It has been pretty wet week so far. At Winchester, we observed about 11 hours of wetness on the 26th with an average temperature of 64F, 50+ hours (and counting) from the 28th to today with an average temperature of 61F. It is certainly long and warm enough for Botrytis infection. Whether we require a fungicide application for Botrytis or not at this point depends on several potential factors. The first one, of course, is whether you had a previous application or not. If you had a previous application to cover these rain events, you probably do not need to be concerned much. The second one is a time to harvest. If you still have several weeks to go, you may want to consider an application, but if you will harvest within a few days, I am not sure an application of fungicide will help you much since we do not have any curative materials for Botrytis. Whatever we spray at this point will be good against future infections, but not the infection happened already. The third is cultivar...

Maybe I should keep posting that rains are coming... Each time I do, it looks like rains disappear. ;) If you have not subscribed to the email list of Dr. Tony Wolf, who is our viticulturist, please do. It always have a wealth of information. In his latest newsletter, he explores potential reasons why some of cultivars are stalling on ripening process this year. Our Chardonnay is still stuck at 19 Brix or so too! The below is a link to his newsletter, but it typically take several days for the newest one to appear. Thus, the best way is to subscribe to his email list (the instruction for subscription is listed on the page too). http://www.arec.vaes.vt.edu/alson-h-smith/grapes/viticulture/extension/VN_options_index.html

Well, I was hoping that the rest of the season would be nice and sunny, but I was little naive. Looks like some portion of VA may be affected by tropical storm Hermine. Plus, probably due to the hot several weeks with no cooling time during the night in August, some cultivars have been very slow to ripen. I was bit surprised to see our Chardonnay is still around 17 Brix this week. Thus, I complied a list of fungicides with relatively low PHI (7 days or less). I cannot cover every single fungicides out there, but I tried to cover common ones. Please click here to download the table from Google drive. NOAA's precipitation prediction for Harmine as of 2 Sept. 2016

I heard that some of early cultivars are ready to be picked on 7-10 days.  Looks like no tropical storms to worry, yet... (crossing my fingers!) There have been frequent thunderstorms went through our area, and some of them (like the one we had last night) resulted in a significantly long wetness event (8 hours). These wetness events, especially the one happens overnight, are preferred by downy mildew pathogen since they produce spores in dark, moist conditions. Please check my previous post on late season downy mildew . As usual, protection is the best approach.  If you have seen some downy mildew on foliage, it would be best if you can mix a protective material (e.g., copper, captan) with a phosphonate (Prophyt, Phostrol, etc). If there is heavy downy mildew already happening, please do not use Ridomil (metaxel) products because they are known to be overcame by the downy mildew pathogen. Some of reds are probably going through veraison, which would be a good timing for...

As many other parts of VA, we have been experiencing thunderstorms running through our area in the past week for so. Yesterday, we had about 9 hours of wetness with an average temperature of low 70's, then followed by a very humid night with an average temperature of mid-60's. These conditions are conducive for downy mildew development. Please check the previous posting for more information on downy mildew management. Also, as veraison approaches near (or happening for some cultivars), please check 12 July posting on late season disease management.

A cool and wet Fourth of July weekend resulted in a very long leaf wetness hours. So far, more than 12 hours of wetness has been recorded at Winchester AREC, and at this rate, it will go on over the night (= potentially it will be a longer than 24 hours of wetness event). As noted in my previous post, the April frost event(s) probably resulted in a prolonged bloom period. Because of that, I have a feeling that some portions of clusters of many of cultivars are still under a critical period for downy mildew, powdery mildew, and black rot for at least one more week. If your vines were protected with materials such as mancozeb (for downy, and black rot), Revus, Forum, Zampro, Presidio, or Ranman (for downy), Luna Experience, Rally, or other DMI (for black rot) or Abound, Pristine, or other QoI (for black rot), you should not worry too much about it. However, if your vines were not well protected, (e.g., last application was more than 12 days ago, or you have missed some of protective ...

At Winchester area, we ended up having a pretty good weekend. There were several periods with rain, but it was not as extensive as the forecast. We received about an inch total over 2-3 days. However, it looks like the central VA received more rain than we did. I would like to share a question I received from a grower today. "With all of the rain events we have had lately and bloom being an important stage for fungicide application Should we spray after a significant rain event before the recommended 7-14 day interval? Specifically, I applied fungicide June 3rd and received quick but heavy rainfall on the 4th and 5th. Riding through the vines it looks as though there is still chemical residue on leaves and clusters. Can I base a decision off of this observation?" It really depends on what you have sprayed, what we are expecting in the next few days, how the vines are maintained (shoot thinning, etc), cultivars, etc, so, I cannot give you a quick answer. Typically...

Our Chardonnay vines are getting close to full bloom, and of course, we are expecting more rain over the weekend. Just an another reminder that from bloom to 4-5 weeks after bloom is the critical period for downy mildew, black rot, and powdery mildew infection on clusters, and at bloom application is very important one for Botrytis management.  Please see recent post about the at bloom fungicide application consideration as well as recent updates on fungicides. This would be the timing where you will thrown in some good materials into your tank mix! It is much easier to protect the vines than try to play a catch up game after disease outbreak,

I noticed that some of our 'Cheloir' vines are in trace bloom and also it has quite a bit of black rot. As I suspected, the cold rains we received were long enough for pathogens beyond Phomopsis to be able to infect vines. If you have not seen black rot lesions on leaves and shoots, the pictures below are good examples. If you click on them, it should open a larger picture. Please note the small dots on these lesions. These are fruiting bodies that contains spores. Once again, most of us will be seeing bloom in the near future, and it will be a start of critical period for so many diseases . Please be on top of your game (shoot thinning, canopy management, and of course, fungicide applications). Mancozeb, as well as both DIM and QoI fungicides are very effective against black rot pathogen. Looks like we are expecting some rains again next week! Black rot on leaves  Black rot on shoots and rachis

Well, it looks like we will see more rains coming in next week or so. Sounds like a typical start of the season for VA vineyards, doesn't it? Since most of vines have 2-10 inches of shoots, our main focus will still be Phomopsis , especially if your vineyard(s) experienced Phomopsis in the past.  At Winchester, we are experiencing 27+ hours of wetness with the average temperature of 48F or so. This will be a low Phomopsis risk event, and counting. Plus, especially if you had a serious downy mildew issue in the past season, it may not be a bad idea to think about downy mildew because the next series of rains for this weekend and early next week may happen when air temperatures will be in 60's and 70's.  As for Phomopsis, a protective spray of mancozeb, captan, etc. is pretty much the only mean of management, but we do have some options for downy after the rain event. So, if you did not spray before this series of rains, but you are lucky enough to have a window for a s...

Several growers contacted me recently to discuss about disease management after recent frost events. Here are my take on it. 1) If you have some damages on your shoots/buds. As usual, you work with the growth of the vine, but not with the calendar dates. If you have lost a lots of growth from the primary buds, you may have to start over your spray program.  If you have mixed growth from the primary and secondary buds, you may need to adjust your spray program based on what may come from the secondary buds, especially around bloom. Flowers from the secondary buds may lag behind, thus, you may need protect flowers for a longer period of time. 2) If you have extensive damages on your shoots/buds to the point that you may not able to expect crops. Based on what I heard, we are not seen this scenario this year. However, if you happened to have the major issue from the frost events, well, first of all, I am sorry.  Second, you still need to have some level of disease managemen...

Please see the message below from Dr. Sara Spayd, who is an extension viticulture specialist at NCSU.  The information is probably more applicable to people in the southern VA, but we have not really seen cold temperature in the northern VA either. While we can enjoy outdoor activities in the middle of December, this warm weather is bit concerning for grapevines.  Let's hope for a gradual temperature drop in the near future... -- Please pass this on to all grape growers: I know this beautiful weather is tempting, but please DO NOT PRUNE - even hedging. Pruning helps to stimulate vine growth. I would not be at all surprised if you see grape buds in some degree of bud swell, particularly the European bunch grape varieties. Those varieties have very little chilling requirement and it was likely met in the few cold days that we have had.  The short predicted cooling pattern for this weekend will do little to harden the vines and buds for any potential cold...

Now the season is wrapping up, and one of questions I get often is “when to spray what to protect your crop at the last stretch”.    Unfortunately (as with everything else), my answer to the question is “it depends.”   But it won’t help anybody, so, let’s go over several potential scenarios and see one of them makes sense to you. Case 1: you are expecting harvest in 2-3 weeks I think many of Chardonnay and other early white cultivars are about to be harvested.   Luckily, around Winchester area, we have had a good stretch of relatively dry weather.   We had rain showers came in several times, but only two of them, one at 8/4 and another one on 8/20 were long enough to initiate major late season diseases, such as Botrytis.   We have three Botrytis trials, but we have not seen evidence of Botrytis outbreak.   Moreover, at Winchester area, a forecast of next rain is on next Tuesday, and it looks like a case of another thundersto...

Since we are expecting heavy rain event on Saturday, plus about to be done with the critical time for cluster infection by downy mildew, powdery mildew, and black rot (which last 4-5 weeks after bloom), I received a several emails about the application timing.  As with other timings, it really depends on so many factors, but here's my take on it.      If you have a history of black rot and downy mildew in your vineyard, you may have a higher disease risks.  If you are in this situation, AND if you think that your previous application was waring off, then you may need to apply some protection before the rain.  However, if your previous application was within 7-day or have not seen many rains, or not having much issue with downy or black rot, then you probably do not need to panic.     A good news is that it looks like we have an opening after the Saturday's rain event.  (then a few more days of rain in the early part of the week)...

Winchester area received a series of rain over the weekend, and it looks like we may see more coming in the next few days.  There were three days of low and moderate Phomopsis infection risk events over the weekend.  Also, humid and warm nights can promote development of downy mildew spores.  At this time of the season, what we typically recommend is either mancozeb or captan mixed with sulfur to protect young shoots and leaves.  The reason why I typically do not recommend a use of newer materials such as Revus or Phosphite for downy or Luna or Rally for powdery is because we want to keep it for the critical time for cluster infection, which is from bloom to 4-5 weeks after bloom.  If this warm temperature continues, the bloom may comes soon, though!!

Two days of intermittent rain brought a low infection risk event for Phomopsis.  Also, these spring rain events can be precursor events for both downy and powdery mildew.  As noted in the previous posts, keep protecting young shoots from these pathogens.  At this point, you can use mancozeb, captan, and sulfur. (Note: for some reason, this post was not posted in a timely manner.  Sorry!)

We have not received precipitation since the 21st, but every night since then has been humid.  Dews that formed 3-4 AM stayed until 9-10 AM in some days.  Once again, these conditions favors downy mildew spore development.  If your vines are covered with a previous application, you do not need to worry about it, but if not (say, the last application was more than 10 days ago, or you had more than 1.5-2 inches of rain since the last application), then you may want to consider a protective application before next thunderstorm hits, which may happen in the next few days.  We are almost through with the critical period, though!