My winter squash has what Mud Baron once described as “jock itch for plants:” powdery mildew. I’ve tried all kinds of notions and potions in the past, but this year I decided to see what the science says about powdery mildew. Our climate where I live in Los Angeles is, unfortunately, ideal for producing this vexing fungus.
Let’s begin with some condensed advice from UC Davis’ Integrated Pest Management page:
- grow resistant varieties
- find a sunnier spot for the vegetable garden
- back off on nitrogen
- sprinkle plants with water mid morning–add soap for more effectiveness
- remove infected leaves promptly and dispose of them
- apply horticultural oil, neem oil or jojoba oil if the temperature is under 90° F. Do not apply any of these oils if you have used sulfur.
For home remedies I turned to advice from Washington State University horticulturalist Linda Chalker-Scott.
How about milk, widely touted as a powdery mildew treatment? According to Chalker-Scott the answer is yes it might work, but you may need to apply milk before powdery mildew appears. And the studies were done with whole milk, so the effectiveness of other kinds of milk have not been tested. Milk has not worked for me in the past, probably because I applied it too late.
How about baking soda? Chalker-Scott is skeptical. Baking soda has never worked for me.
Compost tea? I hate to bring it up as the topic is insanely controversial. I discovered a tempest in a compost tea pot when I tried to write a non-partisan magazine article about it. Let’s just say I ended up leaning towards the skeptical side when I looked at the evidence. Let me know if you think I’m wrong on this, especially if you can leave a link to a peer reviewed study.
What has definitely worked for me in the past is seeking out resistant varieties. I wasn’t smart enough to remember this fact so I’m going to try the soapy water approach and step up to something stronger if I have to. Part of my problem might also be too much nitrogen–my infected squash is in our straw bale garden and I had to apply a lot of blood meal to get it going. More sun would also help but that would involve cutting down a very large tree. I’ll update this post later in the season.
Let’s hear from you . . .
What powdery mildew treatment have you tried and how did it work? Leave a comment and join the conversation!
And I put the question out on the Root Simple twitter feed and got a few divergent opinions:
Christopher Kennedy @ckpfunk Bonide’s Copper Fungicide for organic gardening. I spray every 14 days this time of year instead of every other w/ baking soda.
Alec @Alec I’ve tried horsetail tea, sea-crop, baking soda, compost tea, and neem oil on mildew, but none compare to milk.
Alissa Walker @gelatobaby I just sprayed with a baking soda solution seems to have done the trick so far. And removed all damaged leaves.
Alex Mitchell @alexmitchelleg give the plants some air, water the ground not the leaves. Could spray diluted milk with water on leaves – never worked for me