Q: Does the organic pest control method of steeping cut tomato leaves in water overnight and then spraying on plants work?

A: I’ve heard of gardeners doing this but no one has yet reported their results. Scientists have experimented with extracting solanine and tomatine from tomatoes and using these chemicals as insecticides. They kill insects but not as effectively as nicotine, which tomato leaves also contain, but which is more concentrated in tobacco leaves. As a side note, several vegetables contain nicotine, including cauliflower, eggplant and potato. When I was in Cuba I saw farmers soaking discarded tobacco stems in water overnight, straining it, then using the liquid spray on eggplants. Their eggplant leaves had absolutely no flea beetle damage, which we dread yearly in Georgia.

Lots of garden plants contain chemicals that kill insects besides the aforementioned nicotine and solanine. Yaupon holly has caffeine, peppers contain capsaicin, catnip makes pulegone, lemons have limonene, chrysanthemum has pyrethrin, and cloves produce eugenol. You’re welcome to try the tomato leaf insecticide but remember that the liquid can possibly spread disease to tomatoes, peppers, eggplants and potatoes.

The Nicotine Content of Common Vegetables