WINTER IN CANADA by Hans Peter Pfeifer - Euro Rootstock&Grapevines Inc.
Harrow , OntarioEvery year grape growers ask themselves some important questions: How did the vines make it through the winter ? Do I have some damage and what can I do about it?
Severe freezing damage several years ago started the viticultural roundtable after a lengthy discussion about those two questions. At that time the growers were relying on weather forecast's on TV and some Mini-Max thermometers placed in the vineyards for temperature readings.The long-term averages from Environment Canada suggested 2 major cold peaks between middle of December and the end of February. As a consequence pruning vineyards before March was considered a risky undertaking and most grape growers have followed that rule of thumb, in combination with some field-cuttings of vine-buds.
Over the last 12 years the author developed a procedure to get a more detailed view of potential damage before the pruning starts. Towards the end of February, canes from different varieties and locations are cut and slowly thawed out . Then every bud of the cane was cut with a razor and recorded on a sheet of paper as dead or alive . This provided a good view of possible patterns of damage and the pruning style could be adapted to it.
The big test came in 1994 when the temperatures dropped down to -27 C during a 3 day storm which caused severe damages in the vineyards. The cuttings indicated that there was still life left in the higher buds, but only in mature wood. So the pruning-style was changed to motorized hedge-trimmers and all the canes were cut off at about half . Also, new trunks had to brought up.Since then we have come a long way, and have 8 hobo data-temperature loggers in seven different locations. Those little loggers can be set up easily and can be programmed to take readings at set time intervals. Our loggers are placed within the vineyards at about 4 feet high, which is the international standard of Temperature measuring, and temperatures are read once an hour. With this set up, the loggers are full every 75 days and must be downloaded .The temperature readings are saved as data-files and can be graphed. Now we are able to take a very detailed look at " what happened " . We can see how the winter settles in, if and how fast the temperatures plunge, how long cold-snaps last and how long warm-trends stay.
To evaluate now the potential of damage we have to take in account last year's growing season. The 1998 year started about two weeks early and that stayed throughout the year. As a result the harvest was early, too, and gave the vines a long recovery period ( we define recovery-period as the time after harvest to complete leaf-fall ). This makes it possible for the grape-wood to get very mature and ready for the winter.
However, there are some more factors involved that can differ from farm to farm . These are the effects of the fertilizer, spray schedule, crop load, canopy management, weed control and harvest date.
Only a close look at all the factors combined with cuttings will help to answer those important questions. And that is the main topic of our first meeting on February the 26, 1999.The winter of 1997/1998 was our trial run and everything was to the satisfaction of all the participants. The winter itself did not harm any of the vineyards and the lowest temperatures never dropped below -15 C. However, by comparison we found differences between different vineyards of almost 3 degrees C during the same time and date.
This year is the second year of a close look and so far it doesn't look frightening . The last day of double-digit warm temperatures was on Dec.6 1998 and from there the temperatures dropped gradually both day and night to the first cold-peak on Dec. 22.This should have been enough time for the vines to become fully dormant. After Christmas it stayed cold and we had some significant snowfall, which put out a very nice blanket of insulation around the trunks. At the Euro-farm we had the following lows :
Jan.5 -18.7 C;
Jan10 -19.5 ;
Jan 14 -18.7C
Jan.20 -12.8 C and then
Feb. 22 at 9 am - 20.2 C.
During the low on Jan 10 the temperature dropped to -23.3C and -24C at different locations.There was also a difference of 7 degrees noted from the lake line to inland within an hour's drive. After the warm up to -2 C on Feb22 the author took good pruning canes from 15 different varieties and locations at the Euro-farm and thawed them out before cutting the buds with a razor on Feb. 25 in the afternoon.
Here are the findings :Riesling - 2 locations - 14 % and 16 % main buds damaged
Scheurebe 23 %
Ortega 10 %
Chardonnay-96 19 %
Cab. Sauvignon 25 %
Merlot 16 %
Gamay noir 20 %
Pinot noir 13 %
The hybrids Vidal , Gm 311 and Gm 318 were less than 7%.
Another grape farm had also done intensive cuttings in their viniferas and ranked their main bud damage between 8 and 24 % depending on the variety.
So far this is certainly not a threat to the 99 crop, because changes in the pruning style can make up for the dead-buds, and there were no reports of damage to the pith or the cambium. However, the members of the Roundtable decided to meet again by the end of March and take another look. The winter isn't over yet and a very cautious approach to the pruning seems the best way of proceeding .
We at the Euro -farm will probably start pruning the hybrids in two weeks and always have one eye on the weather.
Supplement to " Winter in Canada 1998 / 99 "written by Hans Peter Pfeifer - Euro Rootstock , Harrow , Ontario , Canada
Just when everybody hoped that the winter was over and we made out pretty good , we got one nasty surprise in the morning of March 8 ,1999 . That very morning the temperature plunged to -23.3 C . However , closer to the lake the drop went only down to -18.7 C. This increased the damage to the buds ,because right before the frost we had a considerable warming-trend and a lot of varieties had already root activity.
The hybrids were hardly harmed , but within the viniferas there is a wide range from " here goes this years crop " to ' what a surprise ".
Almost every farm shows a different pattern , depending on location towards the lake and field and variety lay-out.We at the Euro Farm are going to take the opportunity and we will start a selection program within our propagation- material. This year ,after that frost, the best and strongest plants will be selected and separately grafted .
This will be one interesting topic for the " Fieldwalk " on July the 17 , 1999 at 1: 30 PM
at the Euro Farm in Harrow .Besides that there are about 45 different varieties and clones to look at and hopefully we will have most of the momentarily available growtubes set up in our new planting.
Hope to see you there Hans Peter Pfeifer
PS: please let us know if you plan to attend , by e-mail or phone (519-738-9337 )
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