Potassium bicarbonate for mildews

woohoomanJuly 5, 2013

Well, in years past, I've tried baking soda, neem oil, milk, and vinegar for powdery mildew. Then I found out that plants need to be treated PRIOR to exhibiting symptoms. I had read that potassium bicarbonate was better than baking soda, but had never tried it.

This year, I was going to get a jump on it, but the humidity and heat came about 2 months early... Voila! Powdery mildew.

Recently, I read that potassium bicarbonate could not only control PM, but could actually cure it some -- even after symptoms.

So I went and found some at a wine making shop. I clipped the most affected leaves off my cucurbits and gave all of them a good spraying.

I plan on going with a 1 week schedule for a few weeks and then a 2 week if there's no further damage.

I'll let you all know how it goes later this summer.


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Powdery Mildew is not a disease that relies on heat and humidity. "Powdery mildew spores are carried by wind to new hosts. Although humidity requirements for germination vary, all powdery mildew species can germinate and infect in the absence of free water. In fact, spores of some powdery mildew fungi are killed and germination is inhibited by water on plant surfaces for extended periods. Moderate temperatures (60ð to 80ðF) and shady conditions generally are the most favorable for powdery mildew development. Spores and fungal growth are sensitive to extreme heat (above 90ðF) and direct sunlight."

Here is a link that might be useful: About Powdery Mildew

    Bookmark   July 6, 2013 at 6:20AM
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kimmsr: We've already had this discussion. MY PM shows up when it gets nice and toasty. My cantaloupes are in direct sunlight for 95% of the day. But did you ever think that there might be TEN hours of each and every day during the summer for PM spores to thrive -- NIGHTTIME temps between 60-80 and TOTAL DARKNESS? And that's not counting the hours of the DAY(EARLY morns and eves) when the temps are in that range and the sun begins or ends shining above a fence line.

It's between 60-80F in the day in SoCal for a very large portion of the year. It's not until it gets hot and muggy that it shows up.


    Bookmark   July 6, 2013 at 1:03PM
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Hi Kevin,
Yes, please do keep us updated on your success with the Potassium Bicarb. As a fellow San Diegan, I completely agree with your assessment regarding the obvious influence of humidity on the emergence of PM. Also, I do believe once you have it in your garden, the spores will probably return at some point year after year, at least that has been my experience, and will require prompt and ongoing treatment to keep it well under control. I have had very good results with Neem Oil, but it is pricey and I would love to find a reliable, all-natural, cheap alternative that is kind to the plant, my family's health, and beneficial insects.
2 questions: Did you spray at night? How much potassium bicarb did you use per gallon of water?

    Bookmark   July 10, 2013 at 1:01PM
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Kassie2: Hey neighbor! :)

Yep.. at dusk. And I added 4 tsp/gal.

Regarding my "assessment", I only call 'em as I see 'em. ;)

I agree about the neem--- it's amazing how fast a 10 dollar bill goes. Not only that, but I am also trying to do the whole beneficial insect thing, and I'm not to sure about HOW much damage neem does to them.

Will update shortly. Going to do another treatment tonight.


    Bookmark   July 10, 2013 at 4:37PM
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