Impacts of cold temperatures on wine grapes

Winter injury results in significant direct losses in grape production and even greater losses in wine production. Winter injury from a single event in January 2004 in the Finger Lakes region resulted in direct crop losses of $5.7 million and estimate of lost wine sales of $41.5 million (Martinson and White, 2004). So what do growers need to know about winter injury?

What is winter injury?

Winter injury is freezing damage to wood and bud tissues, caused when cold temperatures reach a critical level. Grape vines have complex mechanisms within their cells that cause them to "harden off" or acclimatize for winter. Exposure to short days and colder temperature through the fall and winter encourages vines to export water from their cells into the spaces between cells. This protects the cell structure, because the crystals that form on freezing can damage tissue structures. It is better to have the crystals form between cells where they do not damage the cells. More and continual exposure to cold temperatures moves vines into deeper dormancy and more tolerance to extremely cold temperatures.

When does it occur?

Winter injury occurs when temperatures drop below the critical level that each species can tolerate. Usually grape vine trunks are more cold tolerant than fruit buds. Damage can occur in the late fall or early winter if temperatures drop quickly. If temperatures warm up, or swing erratically in short periods of time, winter injury is more likely. Unhealthy or stressed vines are more vulnerable to winter injury. Crop load, pruning practices, type of grapes, and variety all impact the susceptibility of the vine to winter injury. Winter injury can reduce yields, kill the vine completely, or reduce life expectancy by making the vine more susceptible to pests such as crown gall.

Where does it occur?

Winter injury is a common weather risk for grape growers in Ontario which is considered to be a cool climate area for viticulture.

What can growers do to mitigate the risk or economic impact of winter injury in vineyards?

  • Production insurance: Crop insurance is purchased before winter, and can give you peace of mind if winter cold kills your fruit buds. Production insurance will cover crop loss due to frost or winter injury. Your premiums will depend on the coverage you choose, your claim history, and the yield potentials of your vineyards. Over time, your premiums can be reduced if you are lucky enough not to have claims. Growers pay 40% of the premium and provincial and federal government share in the remaining 60%. Growers can choose coverage of 70%, 75%, 80% or 85% of their long term average yield. The premium for grape vine rider is paid for by the federal and provincial governments and will reimburse growers for vines killed by the winter, although vine death must reach 12.5% of the vines before a claim is triggered.
  • Select sites less prone to cold: Avoid low-lying areas, analyze the effect of buildings and windbreaks, and seek sites with good air drainage or those located near large bodies of water. These sites are not available to all growers, but should be considered when choosing a vineyard site. More information on site selection can be found on the OMAFRA website.
  • Matching varietal cold tolerance to the site when planting: In areas with consistent cold winter temperatures growers should consider planting European hybrid grapes (Baco noir, Seyval Blanc and Vidal) or North American hybrids (Frontenac, Marquette) that are more tolerant and can withstand temperatures as cold as -25 to -28°C. The majority of commercial wine grape species grown in Ontario are Vitis vinifera (Chardonnay, Cabernet franc, Cabernet sauvignon, Gamay, Merlot, Pinot Noir, Riesling) which tend to be more vulnerable to cold temperatures (most damage occurs below -22°C), but can produce higher quality wine. When planting a vineyard select varieties that suit the climatic conditions. There can be considerable variation in susceptibility to cold between different grape varieties and some varieties (Syrah, Sauvignon blanc and Merlot) are less cold tolerant. Information on differences in cold tolerance in grapes varieties can be found on the website.
  • Cultural practices to reduce winter injury: In areas like Prince Edward County where temperatures get extremely cold, growers will bury cold sensitive vines to attempt to reduce winter injury. In other major production areas (Niagara, LENS) growers "hill" susceptible varieties by mounding dirt around the graft union to protect the trunks from cold temperatures. Good practices include training multiple trunks of different ages to increase the likelihood of retaining some production in case of a cold injury incident. Ensure that vines are not over- or undercropped during the growing season. Keep insect and disease injury to a minimum; healthy foliage will produce the carbohydrates required for good cold hardiness. Do not apply nitrogen fertilizer too late in the season; this will promote extended vegetative growth so vines will not "shut down" early enough to become winter hardy. Practice good canopy management to promote wood hardening.
  • Have a weather mitigation strategy in place: Wind machines can reduce winter injury under radiation frost events in which a warm air layer lies above a colder air layer. Information on the use of wind machines can be found in OMAFRA Factsheet, Wind Machines for Minimizing Cold Injury to Horticultural Crops and on thePDFs/Final_Wind_Machine_Report_2010.pdf"> KCMS website.

What to do when cold weather occurs?

  • Be aware of weather conditions and potential risks: CCOVI collects data on the bud hardiness of grape vines and posts this information on their website. This information helps growers be aware of the potential risk of cold weather, so they can attempt to mitigate it (turn on wind machines) wherever possible.
  • Know how to evaluate winter injury in your vineyard: CCOVI has provided information on evaluating bud injury.
  • Develop mitigation strategies: Use the information collected on bud damage to develop strategies for pruning and vine renewal. Take into bud mortality into consideration when pruning vineyards. Prune cold tolerant varieties earlier then cold sensitive varieties to minimize risk.
  • Make informed decisions about how to manage vineyards after a frost
  • Contact Agricorp to discuss a crop insurance claim: As soon as injury has occurred call in a damage report to Agricorp at 1-888-247-4999
  • Be aware of symptoms of winter injury that may appear in July: Portions of severely winter-injured vines may begin to grow and then collapse around pea-size berry or even later.

Other resources on winter injury and grape include:

For more information:
Toll Free: 1-877-424-1300