Tomatoes Leaf Spots & Blights (6271)

The tomato is a very popular garden vegetable. However, it is subject to several diseases. These diseases can greatly reduce the quality and yield of tomatoes unless you take steps to prevent and control them.

Septoria leaf spot and early blight alternara are two diseases that commonly attack foliage, resulting in a blighting of leaves. Late blight phytopthora can also occur, but is less common than the other leaf blights. These three diseases attack the fruit of the plant also. A fourth fungus disease, called anthracnose, is even more likely to cause serious losses to ripe fruit.

Septoria leaf spot develops on the lower leaves of the plants, appearing as numerous small, circular spots with gray centers. Eventually it may attack all foliage. Inside of these circles are tiny fruiting bodies, called pycnidia, that look like little pepper grains under a hand lens.

Early blight appears first as small brown, roughly concentric, target spots on the older leaves. These spots enlarge to one-fourth-inch or more in diameter. Usually there is some yellowing of the leaf tissue around the larger spots. This also starts with lower leaves and works its way up the plants.

Late blight is more likely to appear during wet weather when temperatures range between 60-70 degrees F. It starts out as irregular, greenish-black, water-soaked areas on the leaves. With enough moisture these areas enlarge rapidly.

A downy white growth may be seen on the margins of spots on the undersides of leaves. The infection also develops on the leaf petioles and stems. All foliage may become blighted in a relatively short time. Tomato fruit at any stage of development can also become infected, producing grayish-green, water-soaked areas. These areas develop a rough surface, sometimes in a zonate pattern.

Anthracnose develops as slightly sunken, circular decayed spots one-half inch or more in size on the ripening fruit. With moist conditions, the centers of these spots become tan. Frequently, these lesions become filled with spore-producing structures. Tomatoes infected with anthracnose are worthless, as they soon break down due to soft rot.

There are several practices to help prevent and control these four tomato diseases:

- plant your tomatoes only once every three years on the same ground

- use disease-free plants

- remove old plant debris from the planting site, or bury the debris by clean, deep plowing

- be sure compost material, if using, is thoroughly broken down

There are several fungicides that work well when you apply them as sprays at regular intervals. Start spraying before the leaves show any spots, or when the first fruit clusters develop. Spray every 7-10 days, according to the label.

For more information on this subject, Please visit the College of Agricultural Sciences Publications Web site.

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