Virginia Grape Disease Updates

This is the second part of "at bloom" fungal disease management tips. P lease refer to yesterday's post as well. The spray timings for Botrytis is at bloom, bunch closure, and veraison.  The pathogen has a wide host range and seems to be active throughout the season, but blooming time is considered as a critical timing because the pathogen can infect flowers without showing symptoms. Please keep in your mind that Botrytis is very well known for its capacity to overcome fungicides.  Thus, a rotation of mode of action groups is a very important aspect of Botrytis management. Mode of action for a particular fungicide can be found as a FRAC code, which you should be able to locate on the label.  Here’s a short list of materials for Botrytis and their FRAC code in parenthesis: Elevate (17), Scala (9), Vangard (9), Switch (9+12), Inspire Super (9+3), Luna Experience (7+3)*, Kenja (7)*, Meteor/Rovral (2), Endura* (7), Pristine* (7+11), Miravis Prime (7+12)*. The materia...

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...