If you were hit by a hailstorm on May 22nd, as we were at RAREC, you are probably making some hard decisions on what to do in the vineyard.
Removal of dead and compromised leaves and flower clusters will help reduce development of fungal pathogens.
Stem wounding will be a big concern especially for vineyards with crown gall. Treatments that aid in wound healing or have bactericidal effects may provide some help. However, shoots severely damaged by hail may need to be pruned out.
New growth will continue to push as weather conditions allow. This new growth should be protected against black rot, powdery and downy mildews as you would in any other year.
Hail causes significant damage to leaves, stems and flower clusters. Following a hail storm plants respond by forming secondary compounds such as tannins and polyphenols to heal wounds on the remaining tissues. Since there are significant amounts of dead tissues following a hailstorm, such as the one last Thursday, some pathogens will be promoted while others will be unaffected.
Botrytis will likely increase on dying tissues. This could lead to an increase in inoculum leading to problems during bloom. This will be very dependent on weather conditions leading up to the bloom period.
Colletotrichum, although relatively rare, thrives under conditions following wounding of tissues. If you have seen anthracnose fruit rot on your grapes in previous years there may be a small increase due to the presence of dead tissues.