Archives for posts with tag: powdery mildew

I didn’t think that tomato plants were susceptible to powdery mildew. At least, I have never seen the fuzzy white spores on any of our vines.

But one of the Country Taste Beefsteak tomato plants has developed the affliction and it is rapidly spreading. Fortunately, the vine had all but stopped producing so there will be very little loss as a result.

I guess this is the downside to this year’s late growing season (and next year, the tomatoes will get the baking soda spray).

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This year, I am determined not to lose the battle against powdery mildew.

It’s probably a futile goal—quixotic, really—because we have suffered it every year that we’ve kept the vegetable garden, starting in 2011. Spores of Erysiphe cichoracearum, the fungus responsible for powdery mildew in cucurbits, are present, brought here from elsewhere by the wind (most likely) or by spontaneous manifestation (not likely but it is easy to understand why people once believed in it).

Sadly, the fungus is well-suited to survival and produces resting spores called chasmothecia (all of this is according to the folks at UC Davis; see “UC IPM Online”) that can—and do—resist the freezing weather that kills off weaker organism over winter. The only way to eradicate it is with fungicide, the most effective of which I have no interest in using.

No, eradication is not the answer; management is. And the key to management of powdery mildew is anticipation and early detection. It will appear—that’s inevitable—so I must be ready for it. And that means starting to spray the leaves of the cucurbits, which in our garden are the cucumbers and squash, with a preventative solution and starting to spray them now.

Last year, I found a good recipe on Late Bloomer’s website (see “Late Bloomer – National Heirloom Expo 2013 – Episode 36”; there is other interesting stuff there) and I mixed up a batch today. It’s a simple concoction of water, baking soda, hydrogen peroxide, and dish detergent (which I suspect is there to help the solution adhere to the plant).

I made a loop through the garden this afternoon, spraying each cucumber and squash leaf as I passed. My intuition tells me that spraying while the garden is in direct sunlight is preferable because the sun will evaporate the water, leaving the NaHCO3 and H2O2 (I have no idea what is the chemical formula for dish detergent but it’s probably too long to fit) behind to coat the leaves and inhibit fungal growth.

For the remainder of the season, especially in the fall when the humidity of summer remains but the nights are cooler, I will have to re-spray on a weekly (or so) basis.

Maybe I can’t win the battle but perhaps if I am diligent, I (and the cucurbits) won’t be routed.