debor039

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, bit...

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. Chan...

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 mode of acti...

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 at Cor...

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 specific material...