Grape canopy management

By Terence Bradshaw

High Summer is here, and this period from after July 4 through early August is the perfect time to apply some canopy management to the vineyard. By thinning and positioning shoots; removing unwanted clusters; and cleaning up trunks, we can significantly increase penetration of sunlight into the canopy and especially into the fruiting zone. This will make for measurably better juice and wine quality, improved winter hardiness, and less disease pressure.

There are a number of practices that should be performed, but the most important is shoot positioning (also known as “combing”). This practice includes separating each shoot from its neighbor and directing the growth into the vertical plane: usually down, for high-wire cordon vines, or up for those on a low wire, vertical shoot positioning system. Once shoots are pointed in the right direction, it’s easy to see where runty secondary or tertiary shoots are in the canopy, and where smaller clusters that are behind in development compared to the main crop are- those can both be removed.

(Retired) Iowa State Extension Specialist Mike White presents a good overview of the concepts and practices behind canopy management in his February 8, 2012 newsletter found here.

There’s a video of some UVM staff doing some (silent) canopy management here.

Ohio State Extension has a nice video here.

While I have you, it’s worth mentioning that we’re not out of the woods as far as disease management is concerned. It has been a difficult year so far with all of the rain, and the frequency of it, to maintain fungicide coverage but I have been seeing mostly clean fruit and foliage in vineyards which have maintained an appropriate spray schedule of 4-5 well-selected and –timed fungicides since prebloom. At this point, phomopsis is pretty much done, and black rot will soon be winding down. Powdery and downy mildews (PM?DM) should be the main focus for disease management, as well as botrytis a few weeks down the road. If this wet weather continues, I would recommend a specific botrytis material such as Flint, Rovral, Vangard, Endura, or Pristine before bunch closure (the point where berries size up to the point where spray material cannot penetrate the cluster to protect fruit from infection). As always, check your Pest Management guide (New York & Pennsylvania or New England guides) and the label, rotate fungicide classes to reduce resistance likelihood, and follow all safety precautions when spraying. Organic disease management spray options include copper (DM, a little PM), sulfur (PM), stylet oil (PM, do not spray before or after a sulfur spray), and possibly some of the biologicals but I don’t know enough about them in regards to their performance against these late-season diseases.

Next week would be a good time to scout clusters for grape berry moth (GBM) webbing which could suggest a need to treat for that insect pest. The threshold for treating this generation is 6% of clusters showing damage, which appears as small bits of webbing in between berries up inside the cluster. GBM is the primary insect pest of established vineyards in Vermont, and if it is the only pest insect need to manage, then some very specific materials with low potential for non-target effects may be used, including lepidopteran-specific materials like Bt, Intrepid, Delegate, or Altacor (the latter has some activity against Japanese beetle). Bt (DiPel and others) and Entrust would be effective materials against GBM for organic growers- the former affects only lepidoptera, while the latter would have some activity against Japanese beetle and some other insects as well.

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