UNIVERSITY PARK, Pa. -- Most backyard gardeners grow tomatoes, but when a crop turns out to be less than appetizing, vegetable enthusiasts often are at a loss to figure out what went wrong.

"By the time you see diseased or poorly developed tomatoes it may be too late to do anything about it," says Pete Ferretti, professor of vegetable crops. "Depending on the cause, there may be little you can do. But next year, you may be able to manage your plants to prevent some of these conditions."

Ferretti lists some common problems afflicting tomatoes and recommends some possible solutions.

--Catfaced and Misshapen Fruit: Misshapen fruit is most commonly caused by improper pollination or from flower parts sticking to the reproductive parts of the plant. "Tomato plants will have malformed fruit when the fruit has set in low temperatures," Ferretti explains. "Malformed fruit is more likely to appear early in the harvest."

--Blossom-end Rot: This malady, which produces fruit with dark, sunken and leathery bottom ends, is caused by calcium deficiency during pollination. Ferretti recommends proper liming, not cultivating around plant roots and taking care not to over-fertilize. "Excess salts in fertilizer can suppress calcium uptake," Ferretti says. "Too little or too much moisture also can upset calcium nutrition, so be sure to mulch and irrigate properly."

--Poor Color Development: Good color fails to develop if temperatures are too high or too low during ripening. "The best red color develops when ripening occurs at temperatures between 65 and 70 degrees Fahrenheit," Ferretti says. "Higher temperatures speed up ripening, but the final color is more orange than red."

Ferretti says tomato color will be affected if summer temperatures rise above 85 degrees F or below 50 degrees F for prolonged periods. "Below 50 degrees F, flavor can be greatly diminished, so don't store tomatoes in the refrigerator," he says.

--Blotchy Ripening, Graywall, Internal Browning: Affected areas of tomatoes with these disorders have poor flavor and off-color. Portions of the tomato will have well-defined margins that remain green, yellow-green or gray-green while the rest of the tomato turns red.

Because these problems can be caused by viruses, nutrition, light intensity, moisture and variety characteristics, no one solution exists.

--Sunscald: This problem appears when green tomatoes on plants with inadequate foliage are exposed to the sun. It appears as yellow or white patches on the exposed section of the fruit. "The patches will stay yellow or white as the tomato ripens, but the tissue usually is so damaged that the patches shrink and the surface dries out," Ferretti says. "You'll see sunscald on plants that have lost foliage from disease or other problems."

--Growth Cracks: Cracked fruit can be traced to several causes. It is common during rainy periods when temperature and humidity is high. "Cracking is especially prevalent when rains follow a long dry period," Ferretti says.

Ferretti says cracking is more likely to develop on fully ripened tomatoes. Tomatoes exposed to direct sun are more likely to develop concentric cracks. "Picking tomatoes before they have a full, deep red color reduces the likelihood of cracking," he adds.

--Leaf Roll: Most tomato plants have a characteristic leaf roll that is genetic in origin, ranging from mild to severe. Ferretti says severe leaf roll can expose tomatoes to too much sun, causing sunscald and other problems.

Leaf roll can show up when plants are severely pruned, or when heavy rains maintain an excessive amount of moisture in the soil. "If you plant on well-drained soil, leaf roll is less likely to appear, but it still can occur during periods of heavy rainfall," Ferretti says.

--Walnut or Butternut Tree Injury: A chemical, called juglone, oozing from the roots and other parts of black walnut or butternut trees can lethally wilt or stunt tomato plants. Ferretti recommends not planting under the tree's canopy or in the root zone.

--Chemical Injury: Tomatoes are highly sensitive to injuries caused by many weedkillers, especially growth-regulating chemicals. Injuries include distorted leaves, twisted stems, flower drop and abnormal fruit. Pesticides can drift from as far away as a half-mile or more.

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EDITORS: To contact Pete Ferretti, please call 814-863-2313.