Aspirin, that old fashioned, common cure-all you probably have in your medicine cabinet, is also helpful to plants. Aspirin, which is acetyl salicylic acid, is quite similar to salicylic acid which occurs naturally in plants. Plants release salicylic acid when under attack by pathogens -- much like a plant world version of taking an aspirin at the first sign of a headache.
Rebecca Brown, professor of plant sciences at the University of Rhode Island, conducted a study in which master gardeners treated plants with aspirin water in different dosages. The study found that with application of 250 to 500 milligrams of aspirin per 1 gallon, or one or two tablets, all of the plants grew well and did not succumb to diseases. Higher quantities of aspirin burned foliage. Aspirin water sprayed directly on seeds resulted in complete germination, compared to partial germination of untreated seeds in a study conducted by Martha McBurney, master gardener at the University of Rhode Island.
Aspirin water in 250 to 500 milligrams per 1 gallon of water can be applied to plants every two to three weeks to help boost their ability to fight pathogens and prevent infections. The liquid is more of a preventive than a treatment for existing problems and is not a registered pesticide. A squirt of mild dish soap in the water helps the solution stick to plant leaves.
Source: https://homeguides.sfgate.com/can-aspirin-used-insecticide-pesticide-82186.html
