Many of you are about to be done with harvest and some may still have a few more weeks to finish this rainy season. This is a reminder for disease management after harvest.
The main reason for you to keep your vines clean after harvest is for winter preparation. Grapevines need to store carbohydrate to survive the cold temperature during the winter. If there is not enough foliage on the vine, it may increase the risk of winter injury. The main target diseases are downy mildew and maybe powdery mildew. I do not typically worry about powdery mildew at this late in the season, unless you already have an on-going outbreak that started a few months ago. Downy mildew is common after late-August in our area and severe infection can result in defoliation. Therefore, in a typical year, downy mildew is the one that I would like to control after harvest.
Since it will be after harvest spray, you do not need to worry about the PHI (pre-harvest interval). Thus, you can apply a combination of mancozeb + sulfur, or simply a fixed copper by itself, especially if you are not too concerned about powdery mildew. Depends on the cultivar, you may need to spray once or twice in a two-week interval.
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