Sunset Magazine (June 1996, p. 54) has an article updating info on the use
of baking soda for control of powdery mildew on roses (based on a recipe
used by researchers at Cornell University). The recipe, to be applied as a
spray, calls for 2 teaspoons of baking soda and 2 teaspoons of SunSpray
Ultra-Fine Year-Round Pesticidal Oil dissolved in 1 gallon of water. My
recollection from an earlier article in Sunset is that it functions by
changing the pH conditions on the leaf surfaces so that it is unfavorable
to mildew growth.
The update article informs readers that university studies at Auburn,
Alabama and Oregon State found leaf damage and reduced flowering in roses
when they doubled the recommended rate of soda and more than quadrupled the
rate of oil recommended by Cornell. So be careful about those
They also report that in the trials by OSU researchers Molly Hoffer and Jay
Pscheidt, "a mix of only oil and water gave nearly the same protection
against mildew as the oil-soda-water mix, and resulted in virtually no leaf
damage" (1% SunSpray oil, or about 2 1/2 tablespoons per gallon of water).
This finding may undermine the idea of changing pH being the key to control
of the mildew. No mention is made of testing just a baking soda-water
solution. (I originally thought the oil was basically acting as a
spreader-sticker, but now I'm not so sure.)
Note: I never found a retail source for SunSpray Ultra-Fine Year-Round
Pesticidal Oil when I was living in the Seattle area and do not know if it
would be considered "organic". I also wonder if a generic light mineral oil
would work about as well. Sunset Magazine readers have confirmed that the
soda-oil-water spray was effective on mildew (but not on blackspot -
another major nemesis of rose lovers). Has anyone on Sanet tried this, esp.
using a different oil product?
>Can someone help me?
>Someplace I had read that either boric acid or baking soda can be used
>to stop mildew on vegetation, but I cannot find a recipe.
>I do not want chemical fungicides with their misnamed inert ingredients
>contaminating my environment. But, the problem is becoming severe.
>Can anyone help me?
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Sheryl N. Swink
Cornell International Institute for
Food, Agriculture and Development
Box 14 Kennedy Hall
Ithaca, NY 14853
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