II. Managing Cold Injured Vines- Oh No 2003/2004 was even worse

Bob Pool and Steve Lerch
Department of Horticultural Sciences
NY State Agricultural Experiment Station
Cornell University
Geneva, NY 14456

Just when we thought we could concentrate on retraining vines and producing grapes, along came January, 2004. The Finger Lakes suffered mightly and much cold injury is reported. The cold events in the two winters were not the same.

How Cold Was It?

The above image was copied and modified from one available at the Northeast Weather Association Web Site.

I modified the figure to show the lowest reported temperature in January, 2004 for the various stations. Note that there were many cases where temperatures fell well below the -11 or -12 temperature where we expect injury to hardy vinifera varieties. Because this was an air mass, many more vineyards in the region experienced the cold events. There are many reports of normally protected vineyards at lake level suffering as much or more than higher elevation sites.

At Geneva, we had -16 degrees and have found very few live vinifera buds.

Dr. Bruce Reisch and his associates did a preliminary evaluation of non-vinifera damage at Geneva and report the following:

Varieties with about 50% or more live buds

Varieties with more than ca. 20% live buds

Varieties with less than 10% live buds

These facts prompted me to prepare these additional comments to the ones made in part I

1. Don't forget the trunks

The pictures above demonstrate two things.

1. Buds can survive and begin to develop shoots, but these may not last the season because of trunk injury (left).

2. A crop may be produced, and the vine seem OK, but trunk injury may prevent the attainment of normal cold hardiness in the subsequent fall/winter. These trunks will die in that subsequent winter. As they dry out, they may develop vertical cracks that are often confused with splitting that might be caused if a liquid filled trunk split when water froze and ice expanded.

Trunk injury is most commonly found near the snow line where air temperature is low and where sun exposure may cause trunk tissue to warm.

Martin Goffinet prepared these pictures which show phloem damage (upper left) and progressively deeper cuts reveal xylem injury. Whenever phloem injury is found, one can assume the cambium has been damaged.

The time to assess trunk injury is around bloom. At that time, live cambia have become active near the previous snow line. A cut will not only reveal damage, but will also show whether the cambium is alive or dead. The bark on a trunk with live cambium will "slip". The newly formed, thin walled cells break allowing the phloem and xylem tissues to separate.

We recognize three possible situations

1. No discoloration/bark slips ­ the trunk is probably not injured, use your normal viticultural practice.
   
2. Discoloration/bark slips ­ the phloem was injured, but a vascular cambium has reformed. This trunk will not fully recover. It should be flagged and replacement trunk(s) trained. The flagged trunks should be removed during winter or the following spring.
   
3. Discoloration/bark does not slip ­ the phloem and perhaps the xylem were damaged, and the vascular cambium has not regenerated. This vine may well collapse during the growing season. If possible, two or more shoots should be trained up as replacements. If the old top dies, the extra shoots will help prevent excessive shoot growth. The old trunk should be flagged and removed as with example two.

This is discussed more thouroughly at a companion web page on trunk injury:

The images above were taken in Washington State by Bob Wample and Martin Goffinet. These Concord vines were severely damaged several years previous. The vines persisted, but were not productive. After the bark was stripped awayk, and live phloem painted white, it can be seen that there was not full recovery. The lower image is cross sections of trunk at different levels from the ground (upper left) to the head (lower right). Note that damage was most severe and recovery least complete near the ground where temperatures were lowest.

This shows why it is important to do trunk renewal and replacement following a hard winter. Trunks brought up from below the site of injury will have a complete ring of functional vascular tissue and ensure future trunk function and vine performance.

OK, I'm going to leave lots of buds, but how will I know if the crop is excessive?

Note that, in spite of the extensive bud injury, cluster weight was quite high in 2003. That was a wet year and berry weights were above average. However, the data do show that cluster counts are meaningful in seasons following winter injury.

The table above can be used to help you decide if you have more crop than you want. For example, a vine planted at 9 x 6 feet that has 36 clusters which will normally be 0.2 lbs at harvest will be cropping at about 3 tons/acre. An adjacent vine with 75 clusters will have a very large potential crop of 6 tons/acre and probably should be thinned.

We never have normal summers - How can I estimate whether the season will mature a normal crop?

The figure shows data for 102 years of Geneva weather. It plots the day of the year at which 1200 Degree Days accumulates vs the Total Seasonal Degree Day Accumulation for that year. Concord grapes reach about half their full berry weight when 1200 Degree Days accumulate. The regression equation indicates that each day of delay will reduce total seasonal accumulation of heat by about 32 DD. On average at Geneva, in Sept. we accumulate 13 degree days each day and in October 4 degree days accumulate per day. Thus a 1 day delay in July will probably mean about a 2 day delay in ripening a variety that matures in September and a 1 week delay for varieties ripening in October.

So just because you have lots of dead buds, don't give up

Its not the dead buds that count, its the live ones.

Remember:

1. The vine requires 3-4 shoots/foot of canopy to get full light interception.

2. Make sure you don’t retain more clusters than the vine can ripen.

3. Even if shoots collapse during the summer, their growth will have helped keep vine balance.

4. Emphasize trunk renewal & replacement until every vine has a new trunk.

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