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less likely to drop as low if the renewal zone is raised higher off the ground.


For example, the fruiting zone of a hanging cane trellis is more resistant to frost injury than a VSP. In addition, canes harden off earlier and have deeper dormancy on a hanging cane trellis than VSP. None of these strategies will succeed if the vineyard is located in a region with a strongly continental climate. The presence of a large body of water removes the extremes of temperature in a region because water has such a high specific heat and also because the heat of evaporation and heat of freezing are so large.


Some regions may have a similar mean temperature but the extremes can be greater.This is known as a continental climate, in contrast to the alternative which is referred to as a marine climate. Visualize the contrast between the climates of Vancouver and Winnipeg. Inherited properties between different grape varieties and different clones can make a difference. Riesling is known for its late bud break and winter hardiness, but it is also known for its late harvest date, which makes it inappropriate for short-season sites. Many vinifera and hybrid vines have short vegetative seasons and have information available on their winter hardiness, but information about the time of budbreak is often hard to find.


The most winter-hardy Vitis species often have shallow dormancy and this trait can inadvertently be passed on to their selected progeny. By shallow dormancy I refer to the property that the vine emerges rapidly from dormancy when the soil temperature begins to increase. If passive methods don’t safeguard your buds, then you may have to use an active method. The best known of these strategies is delayed pruning. The number of days that budbreak can be delayed is variable, but a week’s delay in not an unreasonable expectation for most circumstances. Under extreme conditions, when winter cold injury is expected, coupled with spring frost damage, pruning can be delayed until after


26 British Columbia FRUIT GROWER • Spring 2013


budbreak. It may create an ugly trellis but enough canes or spurs can be selected to produce a reasonable crop in spite of heavy damage. The new buds are quite fragile, so pruning must be done with care to avoid damaging the remaining live buds.


Other active methods such as oil sprays, alginate sprays, ice crystallization bacteria, and plant hormone treatments are not yet mainstream but information is


available about their use and potential effectiveness.


I have seen no information about whether the effects of these treatments are additive — i.e. would an alginate treatment extend the effectiveness of late pruning? The loss of buds due to a late frost can be costly. If it happens once, try to not let it happen again. Perhaps you need a wind machine? — Gary Strachan is listed on LinkedIn.


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