The growing season continues to be cool and wet, and grapevines at the UVM Horticulture Research & Education Center are showing about four to five inches of shoot growth. We are beginning to enter a critical time for disease management. Growers should consider applying a protective fungicide soon that has activity against phomopsis in particular, although anthracnose and, to a lesser degree, black rot may be active, especially in high inoculum vineyards. Organic growers should absolutely begin application of something at this stage in combination with keeping up sanitation of all dead or infected wood , rachises, and other grapevine debris- sulfur, one of the bicarbonate materials (e.g., Armicarb, Kaligreen, etc.), or a biofungicide like Serenade, Sonata, Regalia, or Double Nickel may be used, although there is little good efficacy data on that last class of materials.
I mentioned sanitation- now is a good time to get out and clean up the ‘nubs’ left at the ends of spurs after pruning that will die out and serve as reservoirs for phomopsis and other diseases. While you’re at it, this is an especially good time to thin shoots. Cold hardy grapes trained to a high-wire trellis and in good health can support about six shoots per foot of canopy; select the best developing shoots and break off the others now while they are easily breakable with your fingers. Maria Smith and Dr. Michela Centinari at Penn State recently wrote a good summary of shoot thinning available here. I suggest reading it on the deck this holiday weekend with a nice glass of wine, and getting out in the vineyard next week to set this year’s crop on the right track.
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