The is a followup to Post #G23-054, dated September 2, 2023. But if you want the details, you have to go back to last year, when I first tried to test this, but Mother Nature did not cooperate (Post G22-040).
The point of this is to test citric acid solution (home-made) versus copper soap solution (Bonide Copper Fungicide) as protectants against powdery mildew. So this isn’t about killing an existing infection (a.k.a., eradicants). The question is whether either of these sprays will prevent the onset (or maybe onset and spread) of powdery mildew.
Above you see a single set of pumpkin vines spanning the picture from right to left. So this is literally the same set of plants, in the same location, side-by-side, treated two ways. Two weeks ago, none of these plants had visible powdery mildew. Other, nearby curubits did, though, so it was only a matter of time before any untreated curubits in the area would get it.
To the left of the line, I sprayed them with citric acid solution, twice, in the last two weeks. To the right, Bonide Copper Fungicide, ditto.
The results are clearly visible in real life, and should be visible in the photo as well. Near as I can tell, there is no powdery mildew on the copper-treated side. None. But there’s plenty of it on the side treated with citric acid solution.
My conclusion is that the copper soap from Bonide worked quite well, for me, as a protectant against powdery mildew. The citric acid solution did not. YMMV, for all the reasons outlined in Post #G23-054.
I guess that’s really no surprise, as copper salts of various types have been used as antifungals for plants for … centuries? So this Bonide stuff is, I think, in the same family as Bordeau Mix, an ancient antifungal for plants that is based mainly on copper sulfate. And that, like Bonide Copper Fungicide, has to be applied in advance in order to be most effective.
Hence the DeLorean at the top of the posting. All I need now is a time machine, so I can spray all of my susceptible plants a month ago.
Or maybe, just maybe, even though I hate to spray stuff pro-actively, now that I’m convinced that this stuff is effective, and seems to be fairly harmless (labeled as OK for use in organic farming), and doesn’t seem to go bad (because it’s just a copper-based soap), next year I’ll take the time to spray my plants in late summer, before I see the powdery mildew arrive.
That runs against the grain. But in this case, seeing is believing.
Edit 7/25/2024: I believe these results enough that I just pro-actively sprayed all my squash vines with copper soap. This, even though there’s no sign of powdery mildew yet, in my garden this year. That’s a first for me — actually getting ahead of powdery mildew, instead of waiting until it’s a problem. What a concept.
