Virginia Grape Disease Updates

Unfortunately, many of our vines suffered from frost events that happened over the past weekend (and this morning for some of us). I think I lost about 30-40% of Chardonnay shoots. :(  Here are some disease management tips for dealing with frost-damaged vines, especially if your vines have shoots with several to many leaves open. Minor damage: E.g., < 15% of shoots affected. You probably do not need to alter your spray schedule. Moderate damage: E.g., 20-50% sporadic damage throughout a block. Some shoots are heavily damaged, but others are OK. You may keep your regular spray schedule. If we have an extensive rain event(s), there is some risk of Botrytis infection on the damaged shoots. This pathogen can produce spores on the dead tissues. If you are concerned about a potential Botrytis infection (i.e., you have a Botrytis-prone cultivar and the weather forecast says there will be a big rain event coming soon), you may want to use either captain or copper instead of mancozeb for...

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...

As with many other places in the VA, we were suffering from frost damages.  We experienced several near freezing events this year, and most notably, a few hours of 25F on Thursday morning. Our younger Chardonnay planting (4th leaf) had a bud break around 4/1, and being suffered more from it.  I estimated about 80-90% of emerged shoots are now gone. Our older Chardonnay (8th leaf) is about a week behind, and my visual estimate as of yesterday was about 25% loss.  Some buds/shoots look like they are surviving, but I am not sure how it will go after tomorrow morning... There is a very nice blog post about spring frost from Dr. Michela Centinari at PSU.  If you are interested in, please follow this link. The other items I noticed in our vineyards is damage from climbing cut worm. For us, it always starts from the Eastern side of our vineyard which is facing a small patch of wood.  If it is a warm weather, I would spray for it, but I think I will wait ...

Damages from Monday's frost event showed up a few days after.  About 5-10% of shoots (or leaves) on our Merlot vines which is located near the bottom of a hill showed symptoms.  Some are simply become necrotic, and others are showing mosaic symptoms. Also, although there were drizzles here and there, rains from this weekend were not long enough to be disease events at our location.  However, relative humidity was high (near 100%) throughout the last night.  Such a condition can promote sporulation of downy mildew.

Looks like some of us got a frost bite here and there.  I hear some people got mid-20's this morning.  It is probably too early to tell, but most of our vines seem to be OK so far.  It looks like it went just below 32 in our station, but not by much.  However, these baby vines in our nursery looked pretty frosted this morning.  We will see how it will go.  It takes about 24-48 hours for frost damage to show up, and with mild frost damages, you will see mosaic lesions.

As of 3/29/12, about 20% of our Chardonnay buds and shoots are showing the injuries from the frost event on 3/27/12.  Damages on Merlot is about 5%.  I hope your vines are OK.

This page from Michigan State University Extension describes the temperature threshold to have frost/cold injury on Concord vines.  Hopefully we won't receive any frost at this point. Also, I updated "labels" on this blog.  Now the name of diseases will corresponds to the entry that is either 1) have a picture or 2) discussed in length.

Some parts of the central and northern VA had a cold morning that may have resulted in frost/freeze injuries on your vines.  You may see younger leaves with damaged tissues that are often become like scorched tissues (lower left leaves on the first picture; click the picture to see a larger picture).  Or you may see entire shoots become wilted (second picture; click to see a larger picture).  If only younger leaves are damaged, the shoots will recover over time. It seems like tomorrow's rain event will be a relatively cold one (mid to low 50's) in terms of the disease development.  Hopefully we don't see a major risk event.  We'll see...