BY DUKE ELSNER
June 26, 2009 10:55 pm Wine grapes require summer "canopy management" to maintain vine health and promote fruit development. Left on their own, vines will produce an excess of shoot growth, leaves and fruit clusters. Reducing this excess starts in the winter when vines are pruned to bring them back into a desired shape and size. Once growth gets under way in the spring, there are typically still far more growing points in the vine than are actually needed. Right now, hundreds of vineyard workers are rushing to keep up with rapidly growing vines, accelerated by the recent high temperatures. Leaving too many shoots to grow results in excessive numbers of fruit clusters for the vine to support and ripen -- which is very detrimental to fruit and wine quality. More shoots also mean more leaves; the canopy of the vines becomes dense, limiting light penetration and restricting air flow through the vine. These conditions favor fungal disease problems and slow fruit ripening. The problems of dense leaf canopies don't go away entirely when the leaves drop in the fall. Buds that mature in shady conditions are weaker in terms of winter survival and fruit production in the following year. Summer canopy management rescues vines from the dangers of excessive growth. There are three main parts to the process. As soon as shoots are about a foot long, workers can start "suckering" and shoot thinning. Suckering is the removal of extra shoots from the base and trunk of the vine, while a few well-placed shoots are allowed to grow to serve as replacement trunks for future use. Shoot thinning removes extra shoots from upper parts of the vine, reducing the number of fruit clusters and the eventual leaf density. Once shoots are long enough to reach the first of the several "catch wires" higher in the trellis, teams of workers can start "tucking" the shoots up into the wires to keep guiding the shoot growth upward. This maximizes sunlight interception by leaves, and keeps the fruit clusters in a well-exposed and organized position. This tucking activity is known technically as "vertical shoot positioning" and it may need to be repeated a number of times during the growing season. Later in the summer the continued growth of shoots and new lateral shoots may yet again result in excessive canopy problems. Sometimes vines will be mechanically topped and hedged to improve the canopy at this time. For some grape varieties it's a standard practice to remove a number of the oldest leaves that are directly shading the fruit clusters, aiding in fruit ripening, disease management and harvest. Vine canopy management requires a great deal of hand labor, so it can be a costly part of wine grape production. As you drive by our area vineyards this summer you may be impressed by the neatly managed vine canopies. If you stop at the local wineries you will be impressed by the fantastic results -- world class wines. Dr. Duke Elsner is a viticulture and enology educator for Michigan State University's Extension Service.
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