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...

Our Chardonnay clusters are getting larger and berries are starting to touch each other. It feels a bit early, but here are grape disease management reminders at berry touch/cluster closure stage. Botrytis gray mold: The best management practice is canopy management. Botrytis pathogen likes high humidity, thus, the poorly managed canopy that traps humidity will help them to thrive. This pathogen also needs wounds to develop spores, thus, grape berry moth and other insects plus birds need to be managed too. There is a number of Botrytis materials such as Rovral and Meteor (FRAC 2), Elevate (FRAC 17), Vanguard and Scala (FRAC 9), Luna Experience (FRAC 7 plus 3), Kenja (FRAC 7), Miravis Prime (FRAC 7 plus 12), Switch (FRAC 9 plus 12), etc. Botrytis pathogen is well known for its ability to develop fungicide resistance, so, please rotate FRAC codes!! QoI fungicides (FRAC 11) are no longer the effective material for us due to the development of QoI-resistant Botrytis isolates thro...

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...

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...

Dr. Wayne Wilcox at Cornell University wrote an article on sour rot management on " Finger Lakes Vineyard Notes ". (The link will open a pdf file)  Please check it out.  Results from his research group is showing that 1) good canopy management matters, and 2) management of insect (fruit flies) seems to have a big impact on the development of sour rot.  Since their regions do not have issues with spotted wing Drosophila (aka SWD), even regular fruit flies, which cannot damage grape skin, can still aid transmission of sour rot pathogens.  I know some of us in VA have been managing SDW in the past few years. If you have managed SWD and have seen lower level of sour rot, please let me know.

Some of our early cultivars such as Alandale is changing it color.  It is just a matter of time to see other cultivar to enter phase of veraison.  Hopefully, we will keep seeing dry weather with little bit of rain here and there.... There are several diseases to be considered at this stage.  One of them is Botrytis.  The spray timing for Botrytis is at bloom, bunch closure, and veraison.  The pathogen seems to be active throughout the season, but Botrytis likes berries when they get mature and accumulate more sugar.   As usual, canopy management is the first line of defense against grape disease management and this is particularly true for Botrytis since it tends to develop after a long period (15-17 hours) of high humidity condition. Please keep in your mind that Botrytis is very well known for its capability to overcome fungicides.  Thus, a rotation of mode of action groups is very important aspect for Botrytis management.  The ...

As the harvest approaches (plus recent rain events in some part of VA), I am receiving several emails on sour rot.  It is often confused, but not all late season rots are sour rot.  Sour rot is basically a disease caused by bacteria that form acetic acid, such as Acetobactor and Gluconobactor .  It is often associated with wounds (birds, insects, hail, too much rain, early season powdery mildew, certain very fair-skin varieties, etc), high Brix level (13-15 or higher), warm temperature range (high 60F to mid 70F). Since these bacteria cannot penetrate berry skin tissues by themselves, what we typically recommend is wound management (e.g., bird netting, grape berry moth management, etc.), and many people mention that it works.  However, with a potential role of Spotted Wing Drosophila (or lesser extent, African fig fly), which may able to penetrate skin, there is a possibility that we may see more sour rot in the future.  Luckily, Dr. Wayne Wilcox's group a...

Finally, we are having relatively dry weeks!  Most of us are about to finish critical time where 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, varieties grown, and cultural practice you employ, 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 timing for Botrytis is at bloom, bunch closure, and veraison.   The pathogen seems to be active throughout the season, and the reason we recommend application of a Botrytis specif...

I thought I would wait until the rain stops to update the blog, but rains are keep coming and even when we do not receive precipitations, the air has been so damp that the relative humidity has been above 90% for a while.  It started late night on 9/4, and still going.  So far, I counted about 90+ hours of estimated leaf wetness. The temperature has been between low 60's to mid 70's.  This has been ideal condition for both Botrytis and downy mildew to develop.  As for downy mildew, your berries should be resistant to infection, thus, concern is on foliage infection.  Vines need healthy leaf areas for accumulation of carbohydrate into main trunk in order to survive the winter.  With a concern on the PHI, one of Phosphorous acid or Phosphonate materials should be a good choice.  They also provide a good kick-back activity too. I have covered Botrytis earlier in this blog, so, please click here and here for more information.  If you decided to ma...