By: Danny Hillin and Justin Scheiner, Ph.D. – Texas A&M AgriLife Extension Service
If you ask any winegrower on the Texas High Plains about their greatest fear, you’ll likely get a consistent answer: hailstorms! Throughout a large portion of the state, these sudden and often destructive weather events are a major concern throughout the growing season. The damage from hail can vary from small dings on leaves and shoots to complete canopy defoliation and a devastating loss of the entire year’s crop. Early-season hailstorms can sometimes be less disastrous if the vines are able to recover by pushing new growth from secondary buds, but much of this depends on the vine’s health and nutrient status, the timing and intensity of the hail event, and the overall severity of damage.
If a hailstorm strikes between budbreak and bloom, depending on the amount of damage, winegrape growers may be able to clean up the canopy and prune the vines carefully to regrow a new canopy for that season, and to ensure healthy growth for the next season. In many cases, severe hail damage to young shoots results in regrowth from secondary buds. While little information is available on the relative fruitfulness of secondary buds of different V. vinifera varieties, certain varieties like Cabernet Sauvignon and Syrah appear to produce more fruitful secondary shoots than others such as Riesling or Chardonnay. However, fruit on secondary shoots typically lags behind the primary crop introducing undesirable variability in fruit quality. This may necessitate thinning the remaining primary crop or the secondary crop, depending on the damage and overall goal. Or, it may delay harvest until the secondary crop reaches an acceptable level of ripeness and quality. In some cases, it may be necessary to remove all fruit to allow vines to fully recover.
Later in the growing season, but before veraison, berries that are damaged by hail may either scar over and continue to grow or drop off before rot develops. At this stage, many premium winegrape growers choose to thin out severely damaged fruit to keep the remaining grapes healthy and ripening evenly. Damaged berries may crack or split later on in the growing season as they continue to expand, increasing the potential for rot.
Hail damage after veraison requires immediate and careful management to prevent fruit rot, and it may necessitate an earlier harvest. Depending on the severity of damage, additional protectant sprays are usually required to control rot, and it may be necessary to thin heavily damaged clusters in order to save the remaining fruit.
Larger hailstones dropped during more violent storms may also damage vital vineyard infrastructure, such as drip irrigation components and exposed irrigation piping, making it critical for growers to thoroughly inspect their irrigation equipment after a hail event.
Hailstorms in Texas: A Closer Look
Hailstorms are simply defined as thunderstorms that produce balls of ice (hailstones) which fall from the sky. These are formed when raindrops are carried upward into extremely cold areas of the atmosphere by powerful updrafts, where they freeze. As the frozen droplets collide with more water, the liquid freezes to their surface and they grow larger. Once they have reached a sufficient size and weight, they’re too heavy for the updrafts to support, and they come flying back toward the earth—sometimes at speeds of up to 72 mph, depending on their size (according to the National Oceanic and Atmospheric Administration).
In the Texas High Plains, named for its relatively high elevation of around 3,200 feet, vineyards are particularly susceptible to hail. The higher altitude brings the freezing point closer to the ground, making it easier for hailstones to form even during smaller milder storms that are common throughout the spring and early summer. This geographic characteristic makes hail a frequent and unwelcome visitor to the vineyards in this region as well as in several states to the north.
Protecting the Vineyard: The Role of Hail Netting
Perhaps the most effective way to protect vineyards from hail damage is by installing hail netting. This high-density polyethylene fabric is woven to create a mesh barrier designed to stop hailstones from damaging grapevines. The mesh is flexible enough to absorb the impact of hailstones, while strong enough to protect both the grape clusters and the vine canopy.
Typically, hail netting is secured above or near the top of the vine canopy and draped down to shield the fruiting zone, or even the entire canopy, on single canopy training systems. After the final pruning in winter, growers position the netting around the new shoots to safeguard them from early-season hailstorms.
The initial investment in hail netting can be substantial, but it usually lasts between 5 to 10 years, making it a valuable long-term investment for some producers. For example, a 43-inch-wide hail net with a specific mesh size costs around $0.21 per linear foot, translating to about $1,830 per acre in a vineyard with 10-foot row spacing.
Most growers in Texas report that hail netting does not interfere substantially with their day-to-day vineyard operations. In fact, many routine management practices can continue as normal with the netting in place. However, at harvest it is necessary to roll up and secure netting above the fruiting zone to allow access for the machinery or harvest crews. Once harvest is complete, the netting may stay in place until after final dormant pruning or be lowered to facilitate mechanized pruning operations. In the Texas High Plains, hail netting is typically installed and moved manually, although some vineyards have adopted mechanized systems to make the process easier.
For growers that can’t justify the cost of hail netting, another common mitigation strategy is to adjust vineyard management practices to reduce loss or maintain yields. Leaving “extra” buds on the vines during pruning or boosting canopy growth with additional fertilization are common approaches. If hail strikes, it may naturally thin out some of the canopy and fruit, but if it doesn’t, growers can manage the excess growth later in the season when the threat of hail is less. The challenge of course is that higher canopy densities can affect disease pressure and control, fruit quality, and fruitfulness of lower buds if the canopy becomes overly dense.
Hail Netting’s Effect on Vine Canopy Climate
While hail netting can offer serious benefits to grape growers, it can also come with significant drawbacks that may make it unsuitable. In addition to material and installation costs, hail netting applied on the sides of vertically shoot positioned vines compresses the canopy. This in turn reduces light and spray penetration and airflow within the canopy. In areas with high fungal disease pressure, this may be a sufficient reason to avoid the use of hail nets.
A 3-year study conducted in a Malbec and Pinot Gris vineyard in the Texas High Plains, reported a decrease in light infiltration into the canopy by approximately 25%, as well as an increase and humidity and decrease in canopy temperature which were attributed to reduced airflow. The authors also reported a slight reduction in soluble solids at harvest which is consistent with other research that compared netted grapevines with a compressed canopy to vines that were unnetted. This of course is a simplification as a whole host of factors can impact canopy density and microclimate such as the tautness of the nets, shoot density, leaf size, and cluster density and size. Hail netting is certainly not for everyone, but in the ever-unpredictable world of grape growing, where weather can make or break a season, it may offer a crucial layer of protection allowing premium winegrape producers to focus more on producing a profitable harvest and less on the whims of Mother Nature.
References
Cintineo, J.L, T. M. Smith, V. Lakshmanan, H.E. Brooks, and K. L. Ortega. 2012. An Objective High-Resolution Hail Climatology of the Contiguous United States. Am. Meterol. Soc. 27:1235-1248. https://doi.org/10.1175/WAF-D-11-00151.1
Hillin, D., J. Scheiner, T. Montague, and T. Ruland. 2022. Hail Netting for Vineyards. Texas A&M AgriLIfe Extension Service. HORT-PU-273.
Ruhland, T.K., T. Montague, and P. Helwi. 2023. Impact of Hail-Netting on Vitis Vinifera L. Canopy Microclimate, Leaf Gas Exchange, Fruit Quality, and Yield in a Semi-arid Environment. Viticulture Data Journal. https://doi.org/10.3897/vdj.4.e108805
