Drought Tipping Point: Vines Risk Long Term Damage
As the drought continues to worsen and temperatures across the Midwest exceed 100 degrees, viticulture experts warn that grape growers could face long-term vine damage. If there is no significant rain in the coming days, viticulturalists say crop load, or the number of grape clusters on the vine, should be reduced to ensure plants can survive winter and grow next season.
‘The stress has reached a critical point with the crop,” says Bill Shoemaker, a viticulture specialist who monitors two acres of grapes at the University of Illinois’s Department of Crop Sciences and works with industry groups. ‘If favorable rains occur now growers can continue on as normal,” he says, ‘but if they don’t get good rains within a few days they need to start considering whether to remove some of the crop to preserve the health and vitality of the vine.”
Weeks of heat stress are taking their toll on vines around the Midwest, where the majority of vineyards don’t irrigate and three-quarters of the region is in drought. Bradley Beam, Enology Specialist at the Illinois Grape Growers and Vintners Association (IGGVA) and winemaker at Willett’s Winery in central Illinois says this is not a good year to over-crop vines. Beam says commercial growers aiming for big yields could be among those who risk seriously damaging their vines. ‘Take a look at the vines and if the shoots seem like they’re growing and you’ve got long shoots and you’ve got a good crop on it you’re fine,” he says, ‘ but if you see vines that have noticeably stunted growth and lots of fruit, well, the fruit’s the reason.”
When a vine has fruit it prioritizes its energy reserves for its growing crop, risking the life of the plant when drought conditions reduce the amount of energy available. ‘Vines have the potential to create a lot of energy through photosynthesis,” explains Shoemaker. ‘When they have a very healthy leaf canopy they do that very well but our vegetation cover is much smaller than normal because of the drought and when the plant has fruit on it will divert energy to fruit rather than support itself so I think we’re at a point where in some vineyards they may be facing risk if they don’t remove crop and release some of that energy to the plant.”
Anthony Peccoux, Viticulture Program Leader at the University of Missouri’s Institute for Continental Climate Viticulture and Enology (ICCVE) agrees, and says vine health is very dependent on the condition of the vine canopy and its leaf area to fruit ratio. ‘If there is enough canopy to grow the plant that’s fine. If that’s not the case it could be dramatic,” he says. ‘If the stress is high from drought, or even from factors like a nutrient deficiency or disease, a very high crop load can damage the lifespan of the vine, that’s 100% true.”
Viticulture expert Beam says commercial growers and new vineyard owners often dislike the idea of removing clusters of grapes from their vines, ‘but anyone that’s ever been bitten by that, where they actually didn’t and should have and then saw their vineyard set back two years before they were back up to speed again, they know it is the right thing to do.”
According to US Drought Monitor, the dry conditions have continued to worsen across the Midwest. In its latest report released on 19th July, for the first time since the beginning of this dry spell, the border areas of Kentucky and Illinois are in a state of exceptional drought, the highest rating used by the monitoring group. More areas of the region are now in extreme drought, including southern Wisconsin and central Missouri. 85% of the Midwest is now classified as abnormally dry.