Gardening: Fight against tomato fungus with aspirin mixture

Nancy Szerlag
Special to The Detroit News
Tomatoes and other fresh produce at Eastern Market.

According to the Michigan State University Extension office, we may be in for another tough tomato season.  After weeks of cold wet weather, the forecast calls for warm nights with high humidity, and that’s the perfect recipe for fungal diseases. 

At dinner last week, my brother brought up the subject of using aspirin to stimulate "Systemic Acquired Resistance," often called SAR, in tomato plants, which I have written about before.  Researchers at the USDA and the University of Florida found the active ingredient in aspirin, salicylic acid, will activate and boost a plant’s SAR against bacterial, fungal and viral diseases.   When sprayed with a mixture of 1 ½ 325 mg aspirins dissolved in 2 gallons of water to which 2 tablespoons of mild dish soap has been added to act as a spreader sticker every 3 weeks, it not only improved the plant’s resistance to disease, it also improved growth, increased fruit size and production. This recipe can also be used on peppers. 

Do remember that more is not better as far as number of applications or aspirins used.  Too much salicylic acid can damage the plants.

When using foliar sprays, remember to apply them in the morning or in the evening when the sun is going down, so as not to burn the leaves. And cover the entire surface of the leaves, including the undersides. 

Other methods of protecting tomatoes from soil-borne diseases including early blight is to create a soil barrier to prevent spores from splashing on the plants. Begin by pruning the lower leaves of the plant. I prune up about 6 inches. Then cover the surface of the soil with four sheets of newsprint, taking care to overlap so the area stays completely covered. Dampen the paper and pat it in place so no air pockets remain. Mulch the surface of the paper to hold it in place. One gardener recommended using course sand or small pebbles that will help keep everything in place and prevent moisture from building up around the base of the plant.  In late fall the sand can be turned into the soil or shoveled onto pathways. 

As the season passes and the tomato plants grow, removing the suckers that sprout between the stem and leaf branch when they are small will help to increase airflow around the plant and prevent shading. This also helps deter disease. Google “how to prune tomatoes’’ and you will find all kinds of pictorials that take the mystery out of this job.  

Nancy Szerlag is a master gardener and Metro Detroit freelance writer. Her column appears Fridays in Homestyle. E-mail her at, Ask Nancy.  You can also read her previous columns at