The tree s roots produce a chemical called juglone which is toxic to tomato plants. After your harvest, destroy the plants. Next season, plant varieties resistant to Fusarium and verticillium, and practice crop rotation by growing your tomatoes in a different spot in your garden each time. If you suspect Walnut wilt, next season plant your tomatoes at least 50 feet away from your walnut tree, or else grow them in containers. Older leaves have dark brown, concentric rings on them.
Early blight occurs in humid weather.
The fungus overwinters in residue from diseased plants, and can also be present on the seed itself. Destroy or discard infected plants when harvesting is completed. These sprays won t cure the disease, but they can protect new foliage from the fungus if they are used regularly all season. Late blight is the fungus that caused the great potato famine in Ireland from 1845-1850. It occurs most often in humid weather, during which a gray mildew grows on the undersides of the affected leaves of tomato and potato plants.