Vineyards in many of the northern counties of Georgia have received cold damage on multiple occasions this year. The most recent damage occurred 10 May, which means that grapes were phenologically more advanced that one would have observed with past frost/freeze events. In fact, this is the latest event of this nature that I remember in the last 20 years. It remains to be seen as to how much damage actually occurred. However, there are always questions as to how to address damaged tissue and disease issues that result.
The following virtual meeting recording from Virginia was provided by Dr. Tony Wolf. This includes an update on the frost situation from Tony, pest management from Doug Pfeiffer (some that is very specific to Virginia), disease management from Mizuho Nita, and answers to questions from the field from Tremain Hatch. I would encourage you to go to this link, as it really does address many questions you might have at this moment.
As a synopsis of some critical points:
1. Be careful if you are conducting pruning operations, as you can cause more damage if these operatins are conducted incorrectly. Do not attempt to strip off the injured shoots. You are likely to damage the remaining secondary and tertiary buds. Also, the cost of pruning has to be weighed against the benefit. In trials that have been reported concerning whether or not damaged shoots should be pruned following frost damage, limited advantage has been found in pruning out damaged shoots. However, see the discusson by Tony for some potential impacts.
2. Relative disease control, stay the course on your disease control program unless you are not planning to harvest any fruit at all. I have not heard anyone say that this is their situation yet, but if that is the case, please contact your county agent and we can discuss recommendations for your specific vineyard. Since dead tissue will harbor and increase Botrytis, this disease may be more difficult to manage this year as a result of the freeze-damaged tissues. Growers should consider Botryticides carefully this year, and we do need to check vineyards for fungicide resistance if Botrytis is observed. You may want to substitute captan in place of mancozeb products prior to bloom to further suppress Botrytis; captan is generally considered to be more active against Botrytis. However, mancozeb is generally considered to be more active against black rot, so use of mancozeb prior to, during, and just after bloom would be encouraged. In light of our phenology as compared to Virginia, we may be too close to bloom to really use captan at this point; in which case, we would start captan applications when we can no longer use mancozeb due to the PHI (standard program). However, without regard, you will need to make sure your have your standard critical, most-active Botryticides in place for bloom, berry touch, veraison, and preharvest. Also, leaf pulling and other operations to increase air flow and reduce drying times will be critically important as well.
3. I don’t think that we have significant wood damage, as the temperatures have not been that cold. For grapes that have broken bud, green tissue injury will occur at 27-28F, and we were close to these temperatures at higher elevations on 10 May. At colder temperatures, you will begin to experience cold injury to permanent woody tissues, but again, I think this is unlikely.
Sarah Spayd (past viticulturist at North Carolina State) sent out the following after another freeze event that occurred a few years ago, and it is still very pertinent to this situation.
“DO NOT plan to save money by reducing your spray costs. With the injured tissue and likely chaotic growth to come, vines still need their usual spray program. This is not the year (normal crop, light crop, or no crop this applies) to skimp by not spraying. If you want to save money, back off of any nitrogen applications that you planned to apply this year. If bud numbers are down on the vine, the vigor of individual shoots will be higher as the vine is putting all of its energy into fewer growing points.”
I hope the combination of the Virginia meeting and these comments will be of value to you as you think through your plans relative cold-damaged vines and clusters. Please contact your local county agent should you have additional questions.