Vineyard Management


Spring brings a big puzzler


Growers left to wonder: Was it bud injury, trunk damage or winter kill?


By Gary Strachan T


he spring of 2010 was a wake- up call for many grape growers. Several unusual things


happened. Damage was sporadic. Many vineyards had no damage and others had widespread damage. It didn’t seem to make sense. Low-lying or flat areas are always more susceptible to winter injury than sloping ground, and yet there were patches of stunted growth in healthy vineyards on good sites. There are likely several factors at play here. Individually, the effects would probably not be noticed but when they occur simultaneously there can be an additive effect. The first factor is that of vineyard management strategy. Optimal management of a vineyard produces balanced growth with canes well lignified by the end of September. Leaves are beginning to senesce and shoot elongation has ended. Under this scenario the vines have initiated dormancy and nutrient reserves are already stored in the roots and trunks. If there is an early frost that prematurely defoliates the vines, the vineyard won’t be severely damaged. If frost damage occurs in a vineyard located on a good site, it is probably because of delayed maturation of the vines. The flip side of this situation is that bud break occurs earlier in spring on a good site A late spring frost can damage buds on a good site but the buds on less optimal parts of the vineyard remain dormant longer and are less vulnerable. This becomes visually evident from the contrast between normal growth on canes derived from primary buds and weak growth on canes derived from secondary buds.


20 GARY STRACHAN


Vines with trunk injury, above. Note the strong shoots growing from the base of the trunk. Left, a typical shoot derived from a secondary bud. Note there are only five short nodes beyond the cluster. At fruit set a healthy cane should have already achieved two-thirds of its growth for the season.


No amount of good vineyard management can overcome this problem unless late-spring frosts are a recurring problem at your site. In this case, budbreak can be delayed by late season pruning, especially if you are spur pruning your vineyard. Another problem that can occur with spur pruning is that a cool, wet spring can affect the formation of the


new buds at the base of each cane. In this case, the lower buds that are retained in the spurs may be less fruitful or may crop more erratically the following year than buds farther up the cane.


If you experience this situation on a more or less regular basis, you would be well advised to switch to cane pruning. The buds formed


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