This is an excerpt from http://www.papillonsartpalace.com/aspirinforplants.htm:
"The dosage Martha arrived at after numerous experiments was 1.5 aspirin (81 gr. strength) to two gallons of water. Important note: The tablets should be the uncoated type. She also added two tablespoons of yucca extract to help the aspirin water stick better to the leaves. (The yucca extract can be substituted with a mild liquid soap).
Finally, Martha divised a schedule of spraying once every three weeks, no matter the type of plant. The summer when Martha first started testing aspirin water was not the best, weather-wise. It was cool, rainy and damp. Yet, by the end of the season, the plants growing in the raised beds on which the aspirin water had been used looked like they were on steroids! They were huge and green and insects-free. Some disease seemed even to have reversed themselves on cucumbers affected by a virus."I am so trying this!!!