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Tomato diseases          Send a link to a friend

By John Fulton

[July 10, 2007]  It seems like the tomato is the one plant that just about everybody tries to grow. Some people grow large amounts, while others plant one or two in containers. At any rate, the calls and samples have started coming in to the office already. Most of the samples have spots, brown leaves and dropping leaves, or all of the above. Several diseases hit tomatoes, but two of the more common ones are early blight and seporia leaf spot.

Early blight, also know as Alternaria leaf spot, can affect plants at any stage of development. All above-ground parts are susceptible. The most characteristic symptom of early blight is spreading spots, one-fourth to one-half inch in diameter, that form on lower or older leaves. These spots have dark edges and are usually brown to black in the center. These spots frequently merge, forming irregular blotches. Concentric rings often form creating a "target" or "bull's-eye" effect. Affected leaves develop yellow areas around the lesions. Spotted leaves soon turn yellow, wither and drop off. The fungus may cause lesions on the fruit around the stem end and shoulder. The lesion is usually dark brown to black, up to an inch in diameter and with distinct concentric rings.

Septoria leaf spot can also affect plants at any stage of development. Numerous small, water-soaked spots first appear on the lower leaves. These spots soon become circular to angular with dark margins and grayish centers, often bearing one or more tiny black bodies called pycnidia, which are spore-bearing structures. Individual lesions are seldom more than one-eighth inch in diameter and are usually quite numerous on an infected leaf. Heavily diseased leaves turn yellow, wither and drop off in large numbers, starting at the base of the plant. Defoliation can be severe during prolonged periods of warm, wet weather.

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As for what to do, here is the checklist: First, keep ripe fruits picked off the plants. Second, don't work around tomatoes when they are wet. Next, you can try to improve air circulation, but if your tomatoes are severely affected, you won't want to lose any more leaves. And the final step for this year is to try a fungicide. Mancozeb is probably the recommended one, but it is very hard to find. The other option is use maneb or Daconil, which are much easier to find but probably won't give you great control. The final step for future years is to practice at least a three-year rotation, with good sanitation in the garden.

Another disease that is actually an environmental problem is blossom end rot. There have been several samples of this brought to the office this year. The bottom of the tomato (the blossom end) becomes dark and leathery. The condition is actually caused by a calcium imbalance in the plant due to uneven moisture. The best solution is mulching the area around the tomato with 2-4 inches of mulch. Addition of calcium may or may not help the problem, but almost certainly won't this late in the game.

That being said, enjoy those tomatoes!

[Text from file received from John Fulton, University of Illinois Extension, Logan County Unit]


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