Midsummer vineyard management

By Terence Bradshaw

July 9, 2017

Now that the July 4 holiday is past us, it’s time to really think about getting quality into those grapes on the vines. That doesn’t mean that the work that has gone into the 2017 crop hasn’t yet affected quality: the pruning, shoot adjustment, pest management, and other activities that are needed to keep a vineyard in good shape. But the next two months may be the most important in terms of developing high-quality fruit in this (so far) challenging year.

Pest management should continue to focus primarily on disease management. 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.

Later this 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.

None of this spray talk makes any sense if good cultural management isn’t practiced, and right now that means getting canopies in shape to best expose fruit to the sun for ripening and to control tangled shoot growth. Regardless of the training system used, this is an important tie to position canes. Most Vermont vineyards use a high wire systems, in which case shoots should be separated from one another and directed downward with some leaf pulling around clusters to put them in 50-100% sunlight. If using a low wire VSP or fan system, canes should be trained upward and, again, leaves pulled around clusters to expose them to sunlight. This is also a good time to remove laterals, non-fruitful canes, and any small clusters that are lagging behind the rest of the crop. This practice will arguably have the greatest effect on improving grape ripeness (assuming you have diseases relatively well-managed) of any you perform this year. It will also greatly improve the effectiveness of any spray materials that you do apply, at they can better penetrate the canopy and the canopy can dry better after wetting, which reduces disease pressure as well.

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