We are seeing a lot of powdery and downy mildew on grapes this year. These diseases often get established in the late season after harvest. It is important to maintain healthy foliage all the way until frost to maximize winter hardiness. So managing these diseases is important in years like this. Growers should consider a late season application of fungicides to keep these diseases under control to protect the foliage and assure adequate cold acclimation. Downy can be controlled after harvest (when PHIs are no longer a concern) with phosphorous acid products, mancozeb, captan or one of the newer products such as Presidio, Ranman or Zampro. However, none of those fungicides will control powdery mildew (which is much worse in our plantings). So a tank mix including one of the above with a DMI fungicide such as Rally or Tebuzol would be a good approach. There are several other options for powdery mildew such as Torino, Endura, Quintec, or Vivando, or even sulfur on sulfur-tolerant varieties.
If fruit has not been harvested, then options are limited to a hand full of products with short PHIs: phosphorous acid or captan for downy mildew, and Torino or sulfur for powdery mildew.
Powdery mildew on grapes
Downy mildew on grapes