Good air circulation is important. Select disease-resistant varieties, and plant in March so the plants can produce before the heat. Cage your tomatoes to get the plants off the ground and to allow air to circulate among the leaves. This encourages wet foliage to dry more quickly. Keep your vegetable garden clean.
Early blight is one fungal disease that strikes tomatoes.
This disease spreads first to lower leaves by wind-borne spores or splashing rain. Symptoms include yellowing and browning leaves from the bottom up and large, dark spots on leaves. The spots, which consist of concentric rings, can grow together, covering the entire leaf. Early blight likes stressed plants. Mulch to keep soil from splashing on fruit and foliage.