There are many fungi that cause leaf and fruit spots on tomatoes. The ones described here are similar in that they do not have obvious fungal growth on either the leaf or the fruit spots.

Early Blight

Early blight is caused by Alternaria solani. The fungus causes disease in tomato, potato, eggplant, horse nettle, and black nightshade. First described in 1882, it is now found on all continents. It is very destructive in temperate humid climates. Although the disease is called “early” blight, it can occur on the plant at all stages of development. Early blight can cause a decrease in fruit quantity and quality.

Symptoms. All aboveground parts of the plant can have symptoms of this disease. The fungus can kill seedlings before or after they break the soil surface. It can also cause collar rot in young plants, in which a dark, slightly sunken spot develops on one side of the stem. This spot will either grow completely around the stem or weaken the stem, causing the plant to fall over and die.

Leaf spots are circular, up to 1/2″ in diameter, and dark to light brown. They have a distinct pattern of concentric rings, (insert or link to photo showing target like leaf symptoms in folder) like a target. Spots may occur singly or in large numbers on the leaf. The leaf may turn yellow, then brown, and fall off. Older leaves are usually affected before the disease works up the plant. In a severe infection, the entire plant may be defoliated. Defoliation may cause the fruit to become sun scalded.

The fruit is usually affected at the stem end. One or more firm, depressed rot spots appear on either the green or ripe fruit. The spots usually have distinct concentric rings; they may appear leathery and may be covered with a velvety mass of black spores.

Disease Identification. Target spots (insert or link to photo showing target like leaf symptoms in folder) on the leaves are very characteristic.

Prevention. Use disease-free seed and transplants. Resistant varieties are available. Avoid planting near potatoes or other tomatoes. Avoid injury to the plant, especially during transplanting. Long crop rotations are important. High soil fertility reduces the severity of this disease, as does maintaining plant vigor. Limit leaf wetness by watering early in the day and by watering at the base of the plant. Control weeds, especially horse nettle and black nightshade. Eradicate volunteer tomato plants. Remove or destroy debris immediately after harvest, or at least plow under deeply. See current recommendations for chemical control measures

Septoria Leaf Spot

Septoria leaf spot is caused by Septoria lycopersici. It is one of the most destructive diseases of tomato foliage. The fungus can cause disease on tomato, potato, eggplant, petunia, nightshade weeds, horse nettle, and ground cherry. Defoliation of the plant leads to a decreased yield.

Symptoms. Symptoms of this disease can be found on the leaves and other green parts of the tomato plant. Small, round, yellowish spots appear on the leaves, usually after the first fruit sets. Symptoms generally start on the lower leaves first. The spots later become brown or grayish and may have a yellowish or dark border. On susceptible tomato varieties, leaf spots may be up to 1/8″ in diameter; but they are smaller on resistant varieties. Dark specks or dots appear in the center of the spots on susceptible varieties. These are usually fewer or absent on resistant varieties. Heavily infected leaves fall off, normally starting at the bottom of the plant and progressing upward. Fruit infection is rare.

Disease Identification. Leaf spots are small and may have dark specks in them; no spots on fruit.

Similar Diseases. Similar diseases exhibit somewhat different symptoms. Early blight leaf spots are generally larger (1/2″), have a target appearance, and may have a light-colored ring around each spot. Early blight causes large target-like spots near the stem of green or ripe fruit. Leaf spots caused by bacterial speck and bacterial spot are dark brown to black. They may have a yellow ring around them. These diseases cause dark specks or spots on the fruit.

Prevention. Use disease-free seeds and transplants. Resistant varieties are available and should be used whenever possible. A crop rotation of 1 to 3 years controls weed hosts and, therefore, decreases the level of disease. Planting early may help reduce disease, since the pathogen prefers warm temperatures. Avoid working in plantings when leaves are wet. Stake plants to keep foliage dry and off the ground. Avoid overhead irrigation. Immediately after harvest, remove all debris from the field and bury it. As an alternative, use a rotary `brush-hog’ mower and plow then under debris. These techniques prevent the fungus from moving to other hosts to overwinter on them. See current recommendations for chemical control measures.

Anthracnose Ripe Rot

Anthracnose ripe rot is caused by Colletotrichum coccoides, C. dematium, and C. gloeosporioides. This major tomato disease was first noted in 1879. It is now found in North America, Europe, and Asia. There are many plants affected by these fungi, including tomato, pepper, eggplant, many melons and beans, grape, apple, and many nightshade weeds. The fungi may invade the roots of cabbage, chrysanthemum, lettuce, wheat, and other plants. This disease causes a rot of ripe fruit, which may cause huge losses in the field and during storage. Anthracnose ripe rot is favored by moist weather.