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Diseases of Tomato Fruits

Source: NDSU Extension Service Horticulturist

There are several common diseases of tomato fruits in our area. One of these is blossom-end rot. This disorder first appears on green fruits. Fruits with blossom-end rot develop a water-soaked spot at the blossom end of the fruit. The spot enlarges, and the tissue in the spot shrinks. Finally, the spot becomes sunken, turns dark brown to black in color, and has a leathery texture. Blossom-end rot is a non-parasitic disease and is not contagious. It is caused by fluctuations in soil moisture, excessive use of nitrogen fertilizer and root pruning. Control blossom-end rot by using a balanced fertilizer, avoiding use of high rates of nitrogen, hoeing carefully to avoid injuring roots, watering regularly in dry weather and using mulches to help maintain a uniform soil moisture. A clear plastic mulch is very good for this purpose.

Another common problem is sunscald. The first symptom of sunscald is a light spot on the side of green fruits facing the sun. Later, the area blisters, and finally a large flattened grayish-white spot develops. The surface of the spot is dry and papery. Fungi may invade the spot, causing it to darken. Sunscald is a non-parasitic disease and is not contagious. It is caused by a sudden loss of leaves or any other change that suddenly exposes the fruits to the sun. Leaf spot diseases frequently cause a rapid yellowing and loss of leaves. Tying plants to stakes also suddenly exposes fruits to the sun. Control sunscald by protecting green fruits from the sun. If leaf spot diseases develop, control them.

A third problem is early blight. Early blight causes dark, sunken, leathery or velvety spots on the stem end or upper surface of the fruits. These spots often show concentric rings arranged in a target pattern. Early blight develops first on the leaves, where it forms large dark brown spots with the same target pattern. Early blight can be controlled by spraying with fungicides, such as Captan (Orthocide) or Daconil 2787 (Ortho Multi-Purpose Fungicide) which are available from garden care centers or nurseries. Follow label directions for amount of fungicide to use, how often to use and when to stop using it before harvest.

A fourth problem is soil rot. The sides of fruits touching the ground occasionally rot. Control this disease with a mulch or by staking to keep fruits off the ground.

For future reference, you may want a copy of Extension bulletin PP-659, "Disease Control in Home-Grown Tomatoes," which is available at your county office of the NDSU Extension Service.

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