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 management in order to keep canopy clean so that your vines will crop next year. Vines probably need a decent canopy management to have good penetration of lights to encourage flower cluster formation for next season as well.
If you are not expecting crop this year, you can treat these vines as you may do for younger non-baring vines. You can use a mix of mancozeb and sulfur, or a fixed copper by itself (especially if your vineyards do not have a bad history of powdery mildew) and spray every 10-14 days.
Once again, the main target at this time of the year will be Phomopsis cane and leaf spot. Looks like we are expecting several days with some chance of rain over next 10 days or so.
Here’s an update from our vineyard. As I noted earlier, our younger Chardonnay vineyard was hit very hard. It was not as bad in some vines, but I am still expecting close to 70-80% damages on some vines. For some, like the one from the picture below, we may need to be retrain from lower shoots since majority of buds look very bad. We will see how the secondary buds will do.
Buds on older Chardonnay vines were tighter than the ones on younger ones when we experienced several days with mid-20’s. Damages based on visual assessment were about 5-20%, depending on the vine. Some vines may have a looser canopy later, but nothing seems too serious.
[Please note that long internodes above the buds are for our experiment (we are looking for trunk diseases), you should not have these on your vines. ;)]
Our other cultivars, Cab sauv and Cab franc were most likely tight enough at the time of frost events. I did not see any damage on them.
