Diagnose and Manage Your Tomato Diseases
Department of Crop Sciences
The most commonly occurring tomato diseases in commercial fields and home gardens in Illinois are as follows.
Anthracnose, caused by three fungal species of Colletotrichum, appears on mature and ripe fruit as slightly depressed, circular lesions, which may reach to more ½-inch in diameter (Fig. 1). Concentric rings develop at the lesion center, which are tan to black.
Early blight, caused by the fungus Alternaria solani, occurs as concentric dark spots on leaves, stems, and fruit (Fig. 2). Affected plants may become defoliated and die.
Septoria leaf spot, caused by the fungus Septoria lycopersici, develops as circular spots on leaves, stems, and petioles (Fig. 3). Spots (1/16 to 1/5 inch in diameter) have dark brown margins and tan to gray centers dotted with the fruiting bodies the pathogen.
Bacterial canker, caused by Clavibacter michiganensis subsp. michiganensis, occurs as leaf browning, vascular discoloration, and fruit lesions which have dark brown center and distinct white halo known as the bird’s-eye spot (Fig. 4).
Bacterial spot, caused by Xanthomonas campesiris pv. vesicatoria, appears as small, dark lesions on leaves and black spots on fruit (Fig. 5). Symptoms develop on immature fruit; ripe fruit are rarely infected.
Bacterial speck, caused by Pseudomonas syringae pv. tomato, develops as lesion on leaves and fruit (Fig. 6). Leaf lesions are small, black, often with a yellow halo. Infected fruit develop lesions, which are small, sunken, black, surrounded by dark green halo.
Management of fungal and bacterial diseases of tomato can be achieved by cultural practices and chemical use. Cultural practices include using pathogen-free seed and disease-free transplants, planting resistant/tolerant varieties, sterilizing seedbeds and soil in the greenhouse, crop rotation of 3- to 4-year, crop production in well-drained fields, proper spacing of plants to allow good air circulation, destroying volunteer plants, using clean tools, staking plants, minimizing foliage wetness, controlling weeds, avoiding cull pile in the field, removing and destroying infected fruit, and plowing field after-harvest to burry plant debris. Fungal diseases of tomato can be effectively controlled by using fungicides (e.g., Amistar, Cabrio, Chlorothalonil, Mancozeb, Quadris, Revus, Tanos, Endura, …). Chemical control of bacterial diseases is difficult. Spray of copper compounds (e.g., Kocide, Champ, Cuprofix, …) could protect healthy plants. Application of Actigard and Tanos could help to suppress bacterial diseases.