Sunday, August 24, 2008

The Cornell Formula for Powdery Mildew

On the ACGA listserv, a local CG from City Farms and the Garden of CAYNDness asked about powdery mildew. People answered from all around the states to suggest the Cornell Formula, a natural, baking-soda based spray developed at that University that has shown success against even black spot. Here it is:

In one gallon of water, mix and repeatedly shake:

1 tablespoon baking soda.
2 drops dishwashing liquid or insecticidal soap.
1 tablespoon oil. You can use vegetable oil, but 'horticultural oil' will work better, especially one of the new lighter-weight "summer oils". (Cowboy Gardeners: Do NOT use motor oil or WD-40 or any other such foolish thing.)

I wasn't sure what these oils were about, but I found these commercial brands at Colorado State Extension (SunsprayR, ScalecideR, VolckR), as well as a detailed explanation.

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