Regional Gardening Reports :: National Gardening Association

In the Garden:
Western Mountains and High Plains
July, 2006
Regional Report

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Shade cloth protects tomatoes from extreme summer heat and can reduce disease problems.

Summer Tomato Woes

The summer is sizzling with record-breaking temperatures, and I always get questions about what these high temperatures are doing to the garden. No matter our intentions, Nature has a way of controlling how plants respond. We must be patient and ride the storm and not overreact.

If you grow tomatoes, be aware that summer's heat can put a damper on production. It's a time when problems can crop up, slow down growth, and set back production. So be on the lookout for some common diseases and other problems with fruit and foliage.

Two tomato blights can give gardeners headaches. Early blight is caused by a fungus that lives on plant refuse or in the soil. It usually infects the oldest leaves with small, irregular, brown spots. These spots get larger in a concentric, target-like pattern, and the tissue surrounding them is usually yellow. Later in the season, the maturing fruit is also infected, and large spots develop, usually somewhat watersoaked with the ring or target pattern.

If early blight shows up on your tomatoes, it's very important to begin a spray program using a copper fungicide every 7 to 10 days. Also, when the season is over, be sure to dispose of all the plants and fruit that had symptoms -- in the garbage, not the compost pile.

Late blight is the other fungus that can cause serious harm to your tomatoes. This one comes on during cool and wet weather conditions. Unlike early blight, stems can be hit, usually with brown or black blotches (there is no definite target pattern). The fruit will develop a bunch of brownish, wrinkled areas, which may eventually become mushy.

Use the same kind of treatment as for early blight, and avoid overhead sprinkling, especially in the evenings and during cool weather.

Blossom End Rot
Blossom end rot is not a fungus disease but rather a physiological problem. The aberrations on tomato fruits are caused by improper watering practices while the young fruit are developing. During this developmental stage, calcium must be translocated into the young fruit, and water needs to be readily available for this to occur.

The blossom end of the fruit (the region farthest away from the stem) develops a black or brown leathery lesion that becomes somewhat flattened. This can happen to all or only some of the tomatoes on the plant, and to green as well as ripening fruit.

The best way to avoid this problem is to make sure your tomato plants don't suffer drought stress. Water them thoroughly and deeply once a week. Don't just lightly sprinkle them. On the other hand, don't water tomatoes daily since overwatering is just as bad. Use a mulch to retain uniform moisture and reduce stress conditions.

You may have heard that pruning plants and removing leaves will hasten ripening of tomatoes. On the contrary, removing leaves does not hasten ripening or do anything beneficial for the plant. It cuts down on the amount of food energy the plant can manufacture, and exposes the developing fruit to sunscald injury -- white or yellowish spots on the green fruit. Tomatoes do not need to be in the sun to ripen, so keep the leaves.

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