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Oregon Wine Advisory Board
Research Progress Report
1989
Vine Damage, Recovery Methods, and Future Strategies
After the 1989 Freeze
Porter Lombard
Oregon State University
Characterizing the 1989 Freeze in Oregon
The late winter cold front in early February 1989 brought significant snowfall and low temperatures to
all of Oregon viticulture and caused considerable vine damage in the northeastern and in some western
valleys of Oregon. The lateness of this winter freeze was unusual since most winter damage in the
Pacific Northwest typically occurs from an early winter freeze before vines and trees have hardened.
The 1989 minimums ranged from -13°F in Boardman to -1°F in The Dalles from February 2-10, while
lows in the western valleys were from -1°F in Salem to 8°F in McMinnville (see Table 1). Lowest
minimums occurred in Boardman and Milton-Freewater in the northeast and in Salem, Eugene,
Roseburg, and Cave Junction in the western valleys, where vine damage was most severe.
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Generally, temperatures prior to freeze were mild and higher than the long term average for January,
particularly for the mid-Columbia and northeastern regions (see Table 1), where average January
temperatures were elevated 5-7°F. Also, temperatures in the Willamette Valley were 2-3°F above the 30
year average in January while those in southwest Oregon were nearer the long term average. We think
temperatures under 32°F are necessary to harden the woody tissue and buds, and all regions had
minimums under 32°F throughout January. Robert Wample of the Washington Irrigated Agriculture
Research and Extension Center in Prosser found no loss is hardiness, and in some cases even a gain of
hardiness in some varieties.
A winter freeze event of this magnitude can be expected every 3-5 years in the colder regions of the
mid- and upper Columbia River Basin and Corvallis, The Dalles, and Medford (Table 1). But those lows
are less likely to happen in Salem, Eugene, and Roseburg, where frequency of -1 to 3°F occur on a 1025 year interval.
Extent of Vine Damage
Vine damage was expressed as the loss of primary and also secondary and tertiary buds so that few or no
shoots developed on the canes. Secondary or tertiary shoots that finally developed were weak and very
short for next year's canes. In more severe conditions, trunk damage occurred in the cambium on the
southwest side because of the low temperatures just above the snow line and the deharding effect of the
sun exposure. In many cases, the cambium appeared to recover and shoot development at the vine head
has occurred. But in other cases, only root suckers have developed. Crop loss from bud damage will
occur this season; with severe trunk damage, significant loss of next season's crop will occur while
redeveloping a trunk and canes.
Vine damage was most severe in frost sites where cold air was trapped. Temperatures were probably
several degrees colder in these pockets. Varieties most susceptible to the damage were Merlot, MullerThurgau, Sauvignon blanc, Semillon, Gewurztraminer, Early Muscat Grenache, and Red Flame table
grapes. Chardonnay and Pinot noir had less damage, but still considerable. The hardiest variety was
Riesling, but Cabernet Sauvignon vines were also generally hardier than other varieties. Pruning
immediately prior, within a week, to the freeze event resulted in extensive vine damage. Freeze damage
was greater in general where vines were stressed by drought on shallow soils and in a few instances by a
heavy crop load in 1988. This conditioning could delay hardening and/or recovery. Vine hardening was
enhanced and vine damage lessened by the GDC training systems in several Umpqua vineyards as
compared to either the Lyre or Scott Henry systems. However, one vineyard in the Willamette Valley
with a row of Pinot noir on GDC had extensive damage compared to the traditional upright shoot and
undivided canopy rows. This was probably due to stress in 1988 from overcropping or drought.
In summary, the primary vine damage was due to the low temperatures on either the primary buds or the
trunk Minimum temperatures of -8 to -13°F in northeast Oregon were lethal to vines, buds, and trunks
on most varieties, causing 80% loss this season and the next inmost cases. Although Riesling and
Cabernet Sauvignon had considerable primary bud damage, little crop loss occurred on these varieties
because 3-4 times as many nodes were left at dormant pruning. Vine damage in the Willamette Valley
was limited to buds principally in swales and draws with cold air pockets and on knolls with shallow
soils. Vineyards in more westerly valleys near Eugene, Roseburg, and Cave Junction located where poor
air drainage occurred suffered extensive damage, with a crop loss of 30 to 100% this year. Trunk
damage also occurred in more severe cases. Recorded temperatures were seldom below 0°F in these
areas, but -5°F was reported unofficially in these four western Oregon regions: Salem, Eugene,
Roseburg, and Cave Junction.
Vine Recovery Methods
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The goal of vine reconstruction is retraining without massive cuts. Developing shoots for next years
cane can be done where shoot growth at the vine head is sufficient. If weak shoots develop on this years
cane, they can be spur pruned next winter. However, vine trunks should be checked for dead tissue on
the southwest side, split bark or heavy callousing tissue on the lower trunk due to crown gall. In these
cases, or where no growth develops at the vine head or on canes, renewal of the trunk is necessary, and 1
or 2 root sprouts should be trained for a new trunk Extra sprouts may be necessary for accidental
breakage or for multiple trunks for managing for future freezes. The old vine trunk can be cut out
(removed) 2 or 3 years later. Thinning out unwanted shoots and sprouts will encourage more favorable
development of the remaining ones.
Strategies to Minimize Damage From Future Freezes
1. Site Assessment:
Location and site of the vineyard played a very large role in the freeze damage that occurred this
year, as would be expected. Damage and threat of a freeze are less in western Oregon, but
vineyard sites near the bottom of small westerly valleys had vine damage as extensive as in the
northeastern Oregon region. Since the freeze hazard in these westerly sites may be as high as in
the Columbia Basin (once every 5 years), it may be necessary to use certain cultural methods to
keep the freeze damage to a minimum as discussed below.
2. Variety Assessment:
Among the winegrape varieties, there are several hardier varieties to choose from. I have
categorized varieties as to hardiness and susceptibility to freeze damage based on our experience
of winter freezes in 1972, with lows of -8 to -12°F in western Oregon, and in 1989 (Table 2).
Varieties may vary in susceptibility because of conditions which may affect hardening.
Chardonnay and Pinot noir vines were damaged more in 1989 than 1972 because of
preconditioning. Muller-Thurgau, which has had heavy crops, was damaged considerably in 1989.
However, Cabernet Sauvignon and Sauvignon blanc had more extensive damage in 1972 because
of less hardening, and the 1989 freeze had less effect on bearing vines.
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3. Rootstocks:
Rootstocks that produce excessive vine growth may increase freeze damage because of late
maturing wood, and there are reports that C 3309 contributes to vine hardiness. However,
generally we would expect little root-stock effect. When rootstocks are used, trunk damage and
loss below the graft union necessitates regrafting and requires an extra year to develop a full
bearing vine compared with self-rooted vines.
4. Cultural Approaches:
There are several cultural decisions that can lessen freeze damage in vines, such as delaying
pruning, less pruning severity, less crop load, and cane burying.
Delayed Pruning: Pruning of vineyards insusceptible areas should be delayed as late as possible to
lessen the chance of damage since pruning prior to a freeze (within 2 weeks) can increase damage
due to dehardening. Late pruning also gives you the chance to assess the damage after a freeze in
order to adjust your pruning level. Also, the basal nodes may have less bud damage and, therefore,
spur pruning may be more successful in retraining live buds than cane pruning. Generally, by
February there is little chance of a freeze (except in 1989).
Canopy Exposure: Trellis selection and training which affects sunlight exposure will influence
carbohydrate production and hardiness. We have noted that when non-stressed vines are trained to
a GDC (Geneva Double Curtain) system, less freeze damage occurs because of increased canopy
exposure and cane hardiness. Shoot positioning and proper vine size should be adjusted by
pruning severity.
Pruning Severity: Light pruning (leaving 2 or 3 times the necessary node number) will reduce
freeze damage and increase the chances that enough live buds will be left if there is damage. Final
bud assessment and adjustment can be made prior to bud break
Crop Load: Maintaining an adequate crop load balanced with sufficient growth will produce wellmatured and hardened shoots. A crop in excess of 2 1/2 lbs. per foot of row for an undivided
canopy, or an excess of 4 lbs.for a divided canopy, should be avoided in susceptible areas and
should be cluster-thinned if necessary.
Cane Selection: Mature canes with dark periderms have had better light exposure. This increases
cane carbohydrates and increases cold hardiness. Large canes indicate excess vigor and less
hardiness.
Control of Irrigation: Where irrigation is in use or available, vines should not be drought-stressed,
as indicated by yellow senescent basal leaves and the lack of actively growing shoots at veraison.
However, irrigation near harvest can be damaging, particularly if it results in late growth and
dehardening.
Multiple Trunks: Severe winter freeze will not cause equal damage to both trunks since they often
vary in hardiness. Older or younger trunks may be hardier, so each year a new trunk should be
selected.
Cane burying is a more drastic and expensive system to escape freeze damage, but it is effective.
An extra cane or two can be buried under the soil to assure a return crop. Mechanized cane
burying systems have been developed in Russia and China for vinifera grapes, but none have been
adopted in North America.
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Assessment of Bud Damage
The extent of damage can be made by cutting through dormany buds to look for black (dead) or green
(live) ones. At each node, there are 3 buds with a middle bud as the primary and 2 lateral buds as the
secondary and tertiary. Severe damage occurs if all buds are black Canes should be assessed by placing
them in a warm room for 24 hours and then slicing sequentially through the node parallel to the cane
with a sharp razor blade. If more than 10% of the primary buds are dead, then the pruning level should
be adjusted upward to account for the loss.
Summary
We were feeling smug that we could escape the arctic blasts that are expected every 2 years in central
Washington. But Oregon has had at least 4 damaging freezes to vineyards in the last 20 years. It is
obviously important to minimize their effect and maintain consistent production for Oregon's wine
industry.
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