VT Grape IPM: Diseases showing up in area vineyards

The main management items that should be on the minds of growers right now are disease management, groundcover management, disease management, and maybe some insect management. Canopy management probably needs to wait a little bit.

We have been seeing some symptoms of Phomopsis, a little black rot, and some downy mildew in the vineyards we have been checking in the Champlain Valley, not to mention the unsprayed vines on my deck arbor in central Vermont. The good thing about Phomopsis, assuming that you identify it correctly, is that there are no secondary infections during the growing season. Next year’s infections are caused by overwintering inoculum on canes and rachises from this year’s infections, but the disease does not continue to spread for this season. That means that Phomopsis-infected leaves may not need to be removed to prevent spread this year, but infected canes and wood needs to be removed and preferably burned before next season. Phomopsis is a greater problem issue in years with cool, wet springs. This season did start out cool, with just enough wet to cause some infections. Vineyards, especially if managed with organic practices, should have all diseased wood cut out by the beginning of vine growth. When in doubt, prune it out. Infections on rachises which occurred this past month may not be visible until veraison, so keep your eyes out.

With the relatively dry, cool weather (not counting this hot stretch we’re having this weekend) in June, black rot infection periods have been few, but if vines were not protected or high inoculum was present, we should be seeing lesions now. Black rot does have a secondary infection cycle, where conidial spores may be produced in active lesions, leading to continued infection throughout the summer. Black rot lesions are brown, often circular but with irregular margins, and may have a purplish halo at their margin. The key diagnostic is the presence of small black fruiting bodies, pycnidia, in the center of the lesion. These leaves should be regularly removed and destroyed any time you are passing through the vineyard, especially if you are using organic practices.

Downy mildew is just starting to rear its head. This disease is a little different than the others in that it’s caused by an oomycete, rather than a fungus. Consider it something like a cross between a fungus and a bacteria (I am oversimplifying, but the analogy works for me) in that it requires water to move, reproduces rapidly in warm weather, and forms lesions on leaves from which spores for the next cycle are borne. Downy mildew managemt picks up around now, as the summer heat, and especially warm rains, pop up. For organic growers, copper rotated with LifeGard may be a best option for management of this disease. For non-organic growers, captan, Revus, Ranman, and the Phosphorous acid fungicides (e.g., Phostrol, Rampart) are very effective. A great symopsis of downy mildew management is included in Dr. Katie Gold’s 2022 Grape Disease Control article (go to page 9).

Don’t ignore powdery mildew or anthracnose. The former is fairly easy to manage but easy to get away. If you see it, consider application of stylet oil or sulfur, but not both as they are a very phytotoxic mix. Same with oil and captan- keep those two at least 7-10 days apart in the vineyard.

Managing groundcover now is an important (potentially) non-chemical IPM tool to manage disease. Tall groundcover shades lower leaves and increases humidity in the canopy, which enhances the conditions for disease formation. If you do not have a clean strip (herbicide, cultivated, or mulched) under the vines, be sure to mow, including the strip between vines that the regular alley mower misses.

Some growers may be seeing grape tumid gallmaker, but for most, I don’t recommend management. For those who have it bad, Movento is a good non-organic material.

That should be enough for now.

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