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preventing onion downy mildew next year

Posted by joannaqcw NY 4/5 (My Page) on
Mon, Jul 25, 11 at 11:34

I'm fighting a delaying action against downy mildew on my onions for the second consecutive year, pruning infected foliage and spraying with Actinovate and Serenade. I'll have some onions to harvest, but they're small. What can I do to prevent downy mildew next year?I've destroyed my perennial onions; I am dumping onion debris under black rubber, in the sun, far from, the garden; I will make sure of a 5-year rotation. What else? Does it help to heat the soil with black plastic? To leave the onion beds unmulched over the winter and hope they'll freeze? To drench the soil with an organic fungicide? (Non-OG fungicides aren't an option). Any advice greatly appreciated.

Follow-Up Postings:

RE: preventing onion downy mildew next year

Downy Mildew spores can live on infected plant tissue in the soil until conditions are right, cool, wet weather, for them to grow and get blown throught the air to infect plants so crop rotation may help.
Solarizing might help, but that does not mean black plastic. Two layers of clear plastic are generally recommended to do that. There is some research that indicates that solarization of soil kills beneficial soil microbes.

Here is a link that might be useful: Soil Solarization

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