With two more days of rain on the way, and another week of unsettled weather in the forecast, we are on our way to catching up with our ‘normal’ rainfall. The unseasonably warm weather of January and February has now cooled to more normal temperatures, and vines that were starting to push new buds have slowed a bit. As buds start to push, we are now hurrying to finish our final pruning cuts.
Many have asked me why some vineyards are pruned ‘all the way back’ while others are left with long canes. The answer has to do with several factors; disease control, frost protection and labor utilization.
Disease Control. There are a number of fungal disease complexes, collectively referred to as ‘Eutypha’, or ‘Esca’. These fungal spores are released by the presence of free water….rainfall. Hence, the longer we can delay making the final pruning cuts, the lower the chance of a rainfall induced spore release infecting the vines. The infection site for the vine is at any new, open pruning wound or cut, much as a cut on one’s finger is a potential site for infection.
Disease symptoms progress slowly from the point of infection toward the center of the vine. A dead or dying section of wood within the vine, known as a canker, develops, affecting the productivity of that section of the vine, and in advanced stages, over several years, will kill the entire vine. By doing a ‘partial’ pruning of the vine during the major rain producing months we expose an open wound to infection, but then prune off that infection site with the final cuts done as late in the Spring as possible. This is why you see many vineyards with 12 – 14 inch cane wood left until just prior to bud break. When the canes are cut back to the first two buds, the potentially infected original cut is removed.
Frost Control. As Springtime temperatures start to warm and sap starts to flow in the vine, the first buds to push will normally be at the terminal ‘end’ of the cane. The emergence of new growth can be delayed a few days by allowing the terminal buds to push, and then pruning back to the two base buds. What makes this problematic is there is a high risk of breaking off new buds when removing the brush from the trellis system. If, however, the canes are ‘pre-pruned’ to 12-14 inches and the brush removed during winter dormancy, the final cuts can be made just as the end buds are starting to push. With the majority of the brush already removed, there is little danger breaking off base buds that might have already pushed. A few days of free frost protection can be achieved this way if the operations are timed properly. Some years, a few days can make the difference between frost damage, or healthy, fruitful shoots for the new year.
Labor Utilization. By delaying the final pruning cuts until bud break, we can keep our field workers in the vineyard during a time when there is normally a slack period, waiting until the shoots start to grow and we need to make our first suckering pass.
As 2012 begins to unfold, we are still waiting for buds to push in most vineyards. Rain the next two days will keep minimum temperatures above freezing, but unsettled weather in the coming week will likely present some near freezing temperatures, and frost conditions when the skies clear.