Answer: To be honest I am not familiar with studies of cigarette smoke, but is true that tomatoes and peppers (and other members of the nightshade family) may be exposed to tobacco mosaic virus when smokers handle the plants or when the plants are in contact with tobacco. The virus may live for several years in dried stems and leaves, so a cigarette butt mixed into the soil could possibly lead to infection. The virus can be spread from plant to plant by handling or by insects. Good garden sanitation is a must, and cleaning hands with soap and water or milk is recommended after handling infected plants. Remaining plants may be sprayed with milk as a preventive. It is also true that some tomato gardeners exclude smokers or smoking from the garden area as a precaution.
Symptoms include light and dark mottling of the leaves, curling leaves, and malformed leaflets. Some virus strains may cause the plants to yellow, possibly including the stems and fruit, as well as cause curling, dwarfing, distortion or stunting.
Yellowing can also be a signal of verticillium or fusarium wilt, so you might wish to take a sample for your County Extension to help you identify which problem is affecting your plants. In any case, clean up, remove and destroy any plant debris, be careful to rotate your tomatoes, peppers and eggplants, and try to plant disease resistant varieties in the future.
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