Virginia Grape Disease Updates

Just a quick reminder about the 66-day PHI for mancozeb products. If you are thinking about harvest at the end of August or early September, we are getting very close to the limit. You can switch to captan or copper, but these two cannot control black rot, thus, you may need to add a DMI or QoI fungicide for black rot. At least in our area, it has been dry (relatively speaking) so, depends on where you are, you may or may not need to be concerned about black rot. I see black rot on leaves sporadically in my vineyards, but not in the level I need to be greatly concerned.

It was very nice to see you all at the meeting. Here's the content of my handout. Seasonal grape disease updates For VVA Summer Technical Meeting at Stone Tower Winery 12 June 2019 Mizuho Nita nita24@vt.edu Grapepathology.blogspot.com The critical period for cluster infection: Grape clusters are sensitive to infection by powdery mildew, downy mildew, and black rot from the time of bloom to 4-6 weeks after bloom. The length of this critical time depends on the cultivar, 3-4 weeks for American grapes (V. labrusca),  5-6 weeks for French grapes (V. vinifera), and somewhere between the two for hybrids. Please make sure that you have good coverage during the critical period. In a typical year, once we pass the Fourth of July weekend with a clean canopy, we can relax a bit. We are a week or two ahead of “normal” year, so, you may able to relax sooner this year. Downy mildew: Rainfall is not as intensive as the last year (knock on the woods!), but there are enough to driv...

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...

(Phomopsis leaf spot (plus a lesion of black rot), please note the shoot behind the leaf is showing some necrotic lesions which are also caused by the same pathogen) 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 typically takes a while to establish in the vineyard. It may take 5-6 years for Phomopsis to become noticeable if you start a new vineyard. Ho...

It's approximately 10% bud break on our 10 years old Chardonnay and about 25% on 5 years old Chardonnay. Hopefully, we won't get frosted!!