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Late-season grape disease management tips.

Recent rains and more rains in the forecast made me think of downy mildew. Let's take a look at what the NEWA DMCast model says about downy mildew risks from the past two weeks.

Westfield, NC (South of Stuart, VA)

There were six DM risk events, including one that happened today. 

(Note: we have a new weather station in Bristol. You can check the weather data, but the DMCast model is not working yet. I notified the NEWA about the lack of DMCast outputs.)

Floyd, VA

There were four days with downy mildew risk event(s) since the beginning of the month.

Red Hill

There were four days with downy mildew risk event(s) since the beginning of the month.

Washington, VA

There were nine days with downy mildew risk event(s) since the beginning of the month.

Winchester, VA

There were five days with downy mildew risk event(s) since the beginning of the month.

It looks like there were more downy mildew risk events as we move northwards. Also, recent warm and humid nights can promote the downy mildew pathogen to produce spores. 

According to today's Sentinel Vineyard Group meeting, some growers noted downy mildew, but many growers in the central VA mentioned that their vines have been clean so far. 

If the harvest is coming within 10 days or so and if your vines are very clean, you may not need to take any action. If the harvest is about two weeks away, it is probably a good idea to have at least a phosphorous acid. The decision also depends on what cultivars you have. I would be more careful with downy-mildew-susceptible cultivars such as Chardonnay and Vidal. 

If there were more than two weeks until the harvest, I would consider a tank mix of a protective material and a phosphorous acid. Both Revus and Zampro have a 14-day PHI and Captan and Copper have a 0-day PHI. Please note that we have several cases of Revus resistant downy mildew isolates in VA. Also, many winemakers prefer not to see either captan or copper sprayed within 3-4 weeks of harvest.

Moreover, with more rains coming this week, you may want to consider protection against Botrytis and ripe rot. many of our reds are about to finish veraison, and we often protect berries against these two diseases around veraison. As usual, it will depend on the cultivar, environment, and history, so, please make a decision to match your site(s).

This is a link to my previous post about short-PHI material. For ripe rot, Switch, QoI (Abound, Flint, etc), tebuconazole, or captain are current recommendations. If your vineyard has a history of ripe rot, make sure to mix two modes of action.


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