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
- 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
- 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 the
What to do when cold weather occurs?
- Be aware of weather conditions and potential risks:
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
- 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
- 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