Vineyard hail damage and recovery
A client vineyard in Northern Virginia suffered massive hail damage on May 14, affecting every vine. Shoots were broken off, leaves were punctured, and inflorescences (flower clusters) were torn away from shoots.
These photos were taken about 42 hours after damage occurred. There was almost constant overcast and rain that week that delayed substantial vine growth after the hail event. Although hail is disconcerting any time during the growing season, early season damage is preferable to late season damage for several reasons: 1) crop loss is limited to the individual berries instead of rot that spreads from damaged berries late season, 2) if hail damage occurs very early in the season there is an opportunity to prune severely damaged primary shoots and allow secondary shoots to emerge. At this point a recommendation was made to supplement the spray schedule with a fungicide specific for Botrytis, since this is an opportunistic fungal pathogen to vines with hail damage. The issue with spraying for Botrytis is that most broad spectrum fungicides have only limited effectiveness for Botrytis and are at risk for the pathogen developing resistance to it. Botrytis-specific fungicides exist but are expensive and aren't normally applied this early in the season. However, the vineyard was at a high risk for opportunistic Botrytis infection and there is no scenario in which a Botrytis-specific fungicide would not be applied in this case.
The hail event occurred two weeks and 3 days after bud break so there was some confidence that fruit emerging from secondary shoots would have enough time to ripen during the growing season. The issue at this point was to ascertain what shoots should be pruned off to allow secondaries to emerge. This can be difficult since there are several factors involved. Below are photos taken seven days later on May 21, this allowed for the damage shoots to show signs of damage or recovery. At this point recommendations were made to prune off damaged shoots (see photos below for rationale).
On June 1, two weeks and four days after the hail event another visit was made to survey the damage and (hopefully) the recovery of the vineyard. At this point there were several warm and sunny days to allow the vineyard to recover and express any evidence of secondary shoot growth with inflorescences. This seemed to be variety-specific as Petit Verdot and Cabernet Franc showed extensive secondary growth, whereas Viognier and Sauvignon Blanc showed hardly any secondary growth at all (though this may be more a reflection of overall vigor).
Though fruitfulness is observed to be much higher in Cabernet Franc and Petit Verdot than Viognier and Sauvignon Blanc, it is difficult to attribute a cause. In general the CF and PV are more vigorous and likely had more robust inflorescences that withstood the hail, or at least were more shielded from the hail. But the vigor also pushed secondary shoots which are fruitful, though it's not obvious whether the secondary shoots emerged before or after the hail event. With the excessive vigor in Virginia it's common for buds to push two shoots anyway. But the fact that the surviving shoots on CF and PV are fruitful suggests that the secondaries are fruitful, otherwise fruitfulness wouldn't be observed on all the shoots. As for the Sauvignon Banc and Viognier, we will experiment with pruning shoots that don't contain inflorescences in the hope that fruitful secondary shoots will emerge.