Post-emergence infections cause the seedlings to rot at soil line. This usually occurs within 2-4 weeks of emergence (or transplanting). Foliar Diseases of Tomato Steve Bost Professor Entomology and Plant Pathology EARLY BLIGHT, also called Alternaria leaf blight, is caused by the fungus Alternaria solani. The fungus causes a leaf blight and may cause seedling disease, collar rot, stem canker or fruit rot. Collar Rot and Alternaria Stem Canker of Tomato; Greenhouse Production. Printer Friendly Version of Disease Resistant Tomatoes, Text-Only Trader Joe's / ALDI's Exposé COVID-19 Tomato Disease Identification Chart Tomato Disease Abbreviations / Codes Cold-Adapted (Winter, U.S.D.A. Tissue surrounding the spots may turn yellow. PROBLEMS: Tomatoes are susceptible to many pests and diseases such as blights, blossom end-rot, wilts, bacterial and viral diseases, tomato hornworms, aphids, beetles, and cutworms. It is the most common disease of tomatoes in Tennessee. Lesions on the stems are similar to those on leaves and sometimes girdle the plant if they occur near the soil line (collar rot). If high temperature and humidity occur at this time, much of the foliage is killed. Tomatoes can also be grown in containers at a minimum of 5 gal and 1-2 ft deep, one plant per pot. Zones 9 & 10) Tomatoes Tomatoes ~ Seed Suppliers. The fungus also causes many diseases like damping off, seedling blight, collar rot, stem rot, charcoal rot, basal stem rot, and root rot. Crop Protectants for Controlling Diseases of Vegetable Crops in Greenhouses; Good Agricultural Practices for Greenhouse Vegetable Crops; Foliar Fungal Diseases on High Tunnel and Greenhouse Tomatoes; Sclerotinia/White Mold/Timber Rot Management in Tomato High Tunnels If the seedlings do emerge, they are usually weak and lack vigour. Seeds infected prior to emergence rot and typically fail to produce a seedling.