Q: You wrote about using aspirin water to prevent disease on tomatoes a few years ago. With all the trouble we had this past summer, is there anything new on this? I’d try it if it works.
A: The basic premise is that salicylic acid (the original active ingredient in aspirin) triggers plants to activate their version of an immune system, leading to an improved ability to fight off disease and fend off stresses like drought or cold.
Cornell University research ferreted out that information, but it’s not a straight line to conclude that you can spray salicylic acid on tomatoes and head off disease.
For one thing, aspirin is now made of acetylsalicylic acid – not the exact compound found richly in willow wood and originally used in pain-killing. For another, I’m not aware of any detailed studies that nail down exact dose rates, spray timing, limitations and that kind of thing.
That said, Master Gardeners in Rhode Island did some intriguing field studies in 2005 in which they applied aspirin water (about 1½ tablets of uncoated aspirin per gallon of water) to several kinds of plants every two or three weeks.
They’ve reported that the aspirin water helped with disease resistance. I’ve also read online about other gardeners trying it and reporting decent success.
I did my own test two years ago on tomatoes – comparing aspirin water with the commercial disease-preventer Messenger (which contains harpin, a protein that’s also reputed to trigger plant immune response). The Messenger-treated plants didn’t do any better or differently than untreated plants of the same variety, but the aspirin-treated ones ripened slightly earlier and were a little less quick to fall victim to septoria leaf spot (the bane of my tomato plot).
I’ve read that two or more universities are doing research on this, but I haven’t seen any published scientific reports.
My gut feeling is that aspirin water might help a bit if you apply it early and regularly. No one claims it cures a disease problem that’s already flaring. It’s something that has to be applied as a preventive… i.e. before trouble starts. The field tests used applications every two weeks through the season.
So long as you don’t use more than 2 aspirin dissolved per gallon of water (higher rates could burn tender plant tissue), you’re unlikely to encounter any problems. If you give it a try, let me know how you make out. Maybe try it on a just a couple of plants but not on others so you have something to compare. At least aspirin is cheap.