Early blight is a foliar disease that attacks tomatoes, and sometimes potatoes. The fungal pathogen for the disease overwinters in infected crop residues. The fungus, Alternaria solani, causes early blight. It is very common during warm, and humid conditions. Early blight appears mainly on older leaves at the base of the plant as yellow spots, which later turns into dark brown spots. It can also attack leaf petioles, stems, and fruits. The attack on the fruit occurs mainly on the calyx end.

Control typically requires rotation of tomatoes with other vegetables every three years. However, since you have indicated that your garden is too small to rotate crops, what you need to do is plant certified disease-free seeds or transplants, and plant disease-resistant tomato cultivars. Most mail-order catalogs code their seeds and plants with information about which varieties are indeed resistant.

You can also improve the fertility of the soil to encourage growth of vigorous plants. At the end of the season, be sure to clean up and destroy all plant materials to discourage overwintering of the fungus.

Happy gardening,

The Chicago Master Gardeners