|I have yellow leaves starting at the bottom of some tomato plants? It looks like a rot?|
|Tomato plants naturally lose their oldest (lowest) leaves as they become unproductive. As long as the rest of the plant looks healthy and is putting out new growth, it's nothing to be concerned about. Just trim off the yellowing leaves. However, tomatoes are subject to a number of diseases, including late blight. This will cause small, dark, "watersoaked" patches on the leaves and the tomatoes will have greenish grayish spots on them which then turn brown and hard. If there are no watersoaked spots on the leaves, the yellowing lower leaves are probably nothing to worry about.
Blight disease attacks tomatoes over most of North America. Plants under stress or with a heavy load of fruit are most susceptible. Dark brown spots with concentric rings in them form on older leaves first. Infected leaves turn yellow and die. Tomato fruits may sometimes be infected; a black, sunken, leathery spot forms at the stem end. Warm, moist conditions encourage disease development. The fungus overwinters in plant residues in the soil.
Prevention and Control
Plant in well-drained soil where air circulation is good. Rotate crops and destroy any volunteer tomato plants. Don't wet foliage when watering. Amend soil with compost, and fertilize plants judiciously to maintain plant vigor. Use certified disease-free tomato transplants. Tomato plants with blight slowly lose their leaves, but unless the infection is severe, you can usually harvest mature tomatoes. If you choose, you can use a copper-based fungicide as directed on the product label at first sign of the disease. Hope this info helps!