VT Grape IPM: Shoot positioning, disease management

Happy (official) summer. We’re still in peak diseas management mode on Vermont vieyards, but things are starting to shift a bit. Phomopsis management should be done, but black rot is still a concern as fruit won’t develop resistance to that disease for a couple more weeks. More importantly, ‘the mildews’ (downy and powdery) are a concern. For powedery mildew, which only requires high humidity to cause infection, sulfur, Regalia, and stylet oil are options for organic vineyards; those and the strobilurin (FRAC class 11), DMI (3), SDHI (7), and AP (9) are options for non-organic vineyards. Downy mildew is in another whole biological class of diseases, and organic options for management include the copper materials, Serenade Max, and various potassium bicarbonates; non-organic producers may use a strobilurin, phosphite product, captan, or Revus. The New England Small Fruit Management Guide summarizes these options in a pretty easily-digestible table.

I am deep in the midst of teaching two summer courses now, including my Cold Climate Viticulture course. Tuesday I gave the students a tour of the UVM vineyard, which I hadn’t walked in a good week or so, and was taken aback by the amount of Phomopsis and black rot I saw on some vines. Closer examination revealed that the diseases were restricted to the bottom 2-4 leaves on the shoots. This generally indicates that there was an issue with application when those leaves were sprayed, as I checked my spray records against the NEWA grape disease models and I was pretty well-covered. Last year we installed a new exclusion netting system that we left up on the wires, which my tractor with spray cab won’t fit under. So, we pretty quickly set up an old sprayer for use on one of our other tractors, and while spraying that first time, I was tweaking many aspects of the operation while making my spray– travel speed, fan speed, nozzle orientation, etc. I also noticed that one nozzle had some grit in it and likely wasn’t getting material on like I should have. Lesson learned: calibrate your sprayer and check coverage before you start the season.

We also noticed that my vines were a little yellow, and pretty much begging for some nitrogen. This is a good time to get a last, light dose of nitrogen on your vines before putting it away for the summer so vines can adequately shut down before winter. This is also a great time to apply potassium and magnesium as your soil and petiole tests call for them.

Any time now the bases of shoots will start to lignify and we can start shoot positioning in earnest. Vermont summers are short and relatively cool, and developing and ripening fruit clusters need as much sun as you can give them. That starts with getting the clusters exposed by combing shoots down on high-wire trained vines so fruit are exposed and leaves are more or less under the fruit zone. Low-wire or vertical shoot positioned vines need their shoots directed up and away from developing fruit, again to minimize shading. Make sure shoots aren’t breaking off as you work with them, and if they are, wait a bit to do this. We’ll post more information on this shortly.

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The UVM Tree Fruit and Viticulture Program is supported by the University of Vermont Agriculture Experiment Station, UVM Extension, USDA NIFA E-IPM Program, and USDA Risk Management Agency.

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