Fungal diseases that disfigure tomato leaves and fruits include early blight, anthracnose, and septoria leaf spot. Protect plants with proper siting, spacing, annual crop rotation, and thorough fall cleanup, and by avoiding water on leaves. Choose disease-resistant varieties. When disease symptoms appear, slow their spread by removing and destroying affected leaves.
Diseases that attack the roots and vascular system, such as fusarium wilt and verticillium wilt, cause plants to wilt and die. Choose resistant varieties, and protect plants by rotating crops. When symptoms appear, remove and destroy plants immediately.
Hornworms, moth larvae that consume large amounts of tomato leaves, can be hand-picked and squashed. Other insect pests are less common and can often be avoided simply by interplanting tomatoes with herbs and other pollen- and nectar-rich flowers that attract beneficial insects.
Physiological problems, like leaf curl, blossom-end rot, and cracking, are often tied to sudden changes in soil moisture. Try to keep the water supply consistent by improving soil drainage, watering during dry spells, and using mulch. It’s hard to prevent cracking—certain varieties, including many heirloom beefsteaks, nearly always crack as they ripen.