So are you saying aspirin works for PM or does not work for PM?
It most definitely had an impact on my plants for a short period, with 2-4 aspirin per gallon. "Works" is a funny word because it was not exactly a curative effect and here in the Tropics of Alabama fungi and mildews come back fast after rain. I suspect if there was a useful description to be had for aspirin on my cucurbits it would be along the lines of the dissolved aspirin left a powdered film that interfered with the development of PM and washed off too easily in rain. The idea of using 1 aspirin per gallon did not impact anything I did, but upping the dose helped. This experimentation happened many years ago, when I was very new to a pretty tomato and what it took to make that happen. I asked Opus 5 Claude to clarify the fear I developed about the phytohormone effects of aspirin in my attempts with it and got this response back. Bear with it because it remembers other chats I have with it and references to voodoo lily are an example of my personal account memory influencing machines response.
Claude Opus 5:
Aspirin hydrolyzes in water within minutes to salicylic acid — and SA isn't mimicking a hormone, it is one. A phenolic phytohormone in its own right, the master switch for systemic acquired resistance. What it does is lean on every other hormone axis at once. That's the unease you were feeling.
Auxin — suppressed. SA stabilizes the Aux/IAA repressor proteins and gums up PIN protein recycling, so polar auxin transport goes sluggish. Shows up as fewer lateral roots, shorter roots, slower strike on cuttings. Best documented of the bunch, and the one you remembered.
Gibberellin — suppressed. SA stabilizes DELLA proteins, the brakes on GA-driven cell elongation. Shorter internodes, slower germination, general dwarfing at high dose. Your gibberellin hunch was right too.
Ethylene — biosynthesis blocked. SA inhibits the ACC→ethylene conversion. It's why aspirin turns up in cut-flower vase solutions. On cucurbits this deserves more attention than it gets: ethylene is what pushes cucumber and squash toward female flowers. Damp it during flower initiation and you'd expect a maleward shift and fewer fruit. (That bridge is mechanistic inference on my part — I haven't seen it pinned down in an actual spray trial — but it's why I'd keep aspirin off plants that are setting.)
Jasmonate — actively antagonized. The real cost. NPR1 runs it as a seesaw: SA up, JA down. Jasmonate is your defense against chewing insects and necrotrophic fungi — vine borer, cucumber beetle, gummy stem blight, Alternaria, Botrytis. Powdery mildew is a biotroph, which is exactly why SA touched it at all. But on cucurbits you're trading mildew pressure for borer and blight pressure.
Abscisic acid — synergistic at the guard cell. SA drives peroxidase-generated ROS in guard cells and closes stomata. Less transpiration, but also less CO₂ in — a real dip in photosynthesis for a few days post-spray.
Cytokinin — bidirectional, weaker evidence. Cytokinin amplifies SA defense signaling; heavy SA appears to hasten leaf senescence.
Worth adding a seventh, non-hormonal: SA induces alternative oxidase, which burns carbon without producing ATP. That's the thermogenesis trick in voodoo lily, and in your cucumbers it's just a metabolic tax.
Your dose: 4 × 325 mg in a gallon is about 1.9 mM. Published foliar work mostly lands at 0.5–1 mM, with chlorosis and necrotic flecking creeping in above 2 mM. You were parked right at the edge — which probably explains both why it did something and why it wasn't clean.
And the short-lived part has a clean explanation: SA gets glucosylated to an inactive storage form and methylated to volatile MeSA within days, so the active pool drains fast. SAR is priming, not armor — it decays. It's also not curative; established Podosphaera colonies locally suppress host SA signaling anyway.
For the website answer, potassium bicarbonate plus a light horticultural oil is the pragmatic replacement — contact-curative, pennies a gallon, and no hormone crosstalk to worry about.
end.
My path back then led me to the oils next. One oil, thyme, seemed more broadly useful as a fungicide than neem oil, but it does not seem as effective for insect vectors as neem in my garden. Also, a kill all that does not hurt is a couple tablespoons or less of betadine in a gallon of water. It's called povidone iodine. Worst case is you get a little iodine in your diet, which is good.
But notice this reality. You are spraying. Weekly is best "but ain't nobody got time for that!" So at least twice a month. Really you are just suppressing the aggressiveness of nature long enough to get a crop in and then you are using the aggressiveness of nature to bio degrade and compost all the not useful material you grew for use next year.
Funny how too strong a poison hurts the compost that makes next year's fertilizer. Yin and Yang? Harmony? A peaceful goal? Balance?
Yeah. Thanks for letting me share! And thanks to
@Meadowlark and his non verbal communication skills for drawing out of me some primitive planter person. I enjoyed it and learned about my own journey in the effort.
Who was Charles Darwin? His Son? And how are they related to plant hormones?
Lol that was a time jump and you made it.
