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Downy mildew reminder

Since last week, we are having several nights where relative humidity is very high (>90%) (e.g., 8/9-10, 8/13-15).  This condition favors downy mildew fungus to produce spores.  Unlike others, this pathogen can cause disease after a short rain (90 min at optimum conditions).  Thus, some of short showers we are having here and there this week may be long enough as an infection event for downy mildew.  For example, yesterday's short shower event was probably long enough for downy mildew to spread.  Also, please keep in mind that these showers are often geographically nonuniform and you might have had a longer wetness event.

At this point, a phosphonate (aka phosphorous acid, such as Prophyt) is a good option to control downy mildew.  Some people prefer to include captan to add more forward protection.  The target of this late season application is to keep foliage healthy in order to help berries to mature, and also to accumulate carbohydrates for winter survival.  Your berries are not susceptible to downy mildew at this point.
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Comments

  1. ron burnetteAugust 16, 2012 at 10:06 PM

    I am getting a serious downy mildew outbreak and I can not find a local supplier for phosphorous acid any ideas on where I can find it.

    thanks

    ReplyDelete
  2. Mizuho NitaAugust 16, 2012 at 10:10 PM

    Hi Ron, I am sorry to hear about your situation with downy mildew. I don't know where you are located nor how many vines you have, but you can ask your local extension agent, or visit local co-op. If you have only a few vines (say, less than 100), you can also purchase it from home garden centers or through the internet.

    ReplyDelete

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