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John Fulton

John Fulton
Former County Extension Director

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In The Backyard

Horticulture columns and tips done on a timely basis

Maintaining Tomatoes - from Mike Roegge

Posted by John Fulton -

The summer garden has taken its time to mature, but many are finally finding the fruits of their labor are at the peak of quality. The problem has been the unusually cool weather of July. Statewide, July was the coldest on record. One weekend we set record cold temperatures on two of the three nights. Tomatoes are a heat loving crop, and they just did not mature well with that cold weather.

The other problem has been with tomato diseases. As in past years, there are plenty of diseases to go around. The most common are septoria leaf spot and early blight. Both are fungal diseases that can overwinter in plant residue in the soil to reinfect the tomato plant the following season. They both require wet leaves (dew or rain) to infect.

Symptoms of septoria are very small, 1/8" across circular spots, with dark margins and grayish colored centers. You will also find much of the tissue between these spots has turned yellow. Early blight spots are larger, up to 1/2" across and are dark colored. You can find dark concentric rings (somewhat resembling a target) within this area.

It is too late to do much this year, but you can take steps to reduce them next year. First, rotate the area you plant tomatoes in the garden. Do not plant in the same area for at least two years, and also avoid areas where potatoes were planted as well, since they are in the same family and the same diseases can infect both.

Use some sort of ground cover (straw, newspapers, etc.) to prevent soil from splashing on the lower leaves. Since the disease can overwinter in the soil, eliminating the disease containing soil splash will help reduce the disease spread. These diseases spread from lower leaves to upper. When you notice discolored leaves, remove them.

Staking or caging plants will help with air circulation, which will allow leaves to dry quicker. Eliminate all residue from the garden. Compost it. Till the garden in the fall to help aid decomposition of any plant residues. If all else fails, there are some fungicides that can offer some help.

Other tomato diseases that are common would include bacterial spot and bacterial canker. Bacterial spots are very small, 1/16" in diameter and dark colored. In between these spots the leaves will turn yellow. This is one of the only tomato diseases you might find in the upper part of the plant first. Bacterial cankers are much larger dark spots, sometimes over an inch in size. They are almost always found on the margin of the leaf and are brown colored. For both bacterial diseases, follow many of the same recommendations listed above. Copper products can help in their control.

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