Vineyard management approaching bloom

By Terence Bradshaw

Grapes are at 10-12” growth in most Vermont vineyards, and combined with the wet, cool, rainy weather, are at prime susceptibility for phomopsis, black rot, and anthracnose. Fungicide coverage should be maintained on 7-10 day intervals during this extended rainy stretch; if it dries out as expected at the end of the week, spray intervals may be stretched to 10-14 days. Best material options are captan or mancozeb with or without a DMI (e.g., Rally, Tebstar), although I would recommend the DMI given how wet it’s been. Strobilurins (e.g. Flint, Sovran, Quadris) are also effective, but best saved for later when Downy mildew is a concern.

Inflorescence is well-developed, and we can see the potential for the 2017 crop now, so this is a good time to continue shoot thinning, removing the shoots with the weakest clusters if possible. This is also an important time to maintain good weed control, as the period of most rapid growth coincides with a need for moisture and nutrients. It won’t necessarily stay this wet for the whole summer, and if weeds aren’t managed early, the vineyard can become a jungle later in the summer. I do not recommend glyphosate herbicide at this point of the season, there is just too much chance for causing vine damage. Postemergent contact herbicides like glufosinate or paraquat (be extra cautious applying the latter) can be effective in knocking back annual and (to some degree) perennial weeds. Cultivation also works well if the proper equipment is used, but is likely difficult to perform on wet soils. The time period needed for good under-vine weed controls isn’t long; by July, the vines begin to slow growth and shift resources toward developing fruit so a little weed growth is okay by then. But for now and in the next week or so, think about getting those weeds under control.

Insects are a relatively minor concern for Vermont vineyards, with a few exceptions. We are seeing a bit of grape tumid gall in the UVM vineyard this year. This is an infrequent pest that causes visually striking but relatively insignificant damage to the vines, and management practices are not recommended against them. Grape berry moth is the next insect to note in vineyards, although it likely won’t be active for another couple of weeks. Traps are available from Gemplers or Great Lakes IPM to assess flight patterns in the vineyard. Generally, one application of a narrow-spectrum material effective against lepidopteran pests such as Intrepid, Delegate, or Altacor (see other options in the 2017 New York Pennsylvania Grape IPM Guidelines), applied 10-14 days after bloom followed by another application 10-14 days after that will generally manage that pest for the season. Better management may be performed by scouting clusters and applying one of those materials or a Bt product immediately upon the first signs of larval feeding. There is also a good grape berry moth degree day model in the NEWA system that may be of use in your vineyard.

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