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Tomato Problems

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Larry A. Sagers Regional Horticulturist Utah State University Extension Thanksgiving Point Office All rights reserved

Tomatoes are the most popular vegetable grown in home gardens in America. They are productive, require only a small area and bear repeatedly. They are easy to grow and are widely adapted with many uses for cooking, fresh eating and preserving. The fruit is rich in vitamin C and low in calories. As with anything else we like, they also have their share of problems. One of the most notable problems this year has been flower drop. Flower drop occurs when nighttime temperatures are lower than 55 degrees F. or if daytime temperatures are above 95 degrees. Hot, dry winds intensify this problem. If it sounds like I have just read the weather report, you will know why many gardeners are not getting good yields on their Hope for better weather because there is not much else to do. Tomato fruit set may have helped in the early spring but does not work in hot weather.

Blossom end rot is another very common problem. It appears as a depressed, brownish area on the blossom end. The affected areas are one half to two inches in diameter. The leathery spot is not harmful but the affected tomatoes are poor quality. The condition is caused by a calcium imbalance in the plant. Garden texts written in the eastern United States, recommend control by adding calcium to the plant. That control does not apply here! We have too much lime in our soil already. Control the problem by even watering, not too wet nor dry. Do not cultivate deeply and damage feeder roots. Use mulch after the tomatoes start to set fruit.

Fruit cracking varies with variety. As with blossom end rot, cracking is increased by variations in soil moisture. Cracking is worse if water gets on the fruit. One variety I have grown that is resistant to cracking is Celebrity. Other problems with tomatoes include sunscald and poor color. Sunscald is worse on tomatoes exposed to the sun. The high temperatures retard the development of good color. Sunscald is localized damage to the tissue and is prevented by a good foliage cover. Oft time’s tomatoes tend to be very misshapen on the blossom end and have large amounts of scar tissue. Cold weather at the time of blossom set intensifies the deformities but damage from insects also causes cat facing or distortion. Cat facing is generally a problem on extremely large fruited beefsteak type tomatoes.

Another common symptom, leaf curl, has three different causes. The older lower leaves of some varieties curl and become stiff and leathery. The problem is greater with high light intensity and hot dry weather. Fruit is not affected by this condition and the tomatoes grow normally except for curled leaves.

Other causes of leaf curl are more serious. Tomatoes are very sensitive to injury from 2, 4-D, a common lawn weed killer. Exposure to 2, 4-D causes distorted leaves, twisted stems, flower drop, and fruit abnormalities. Do not use these products near tomatoes or when temperatures exceed 85 degrees F. Do not use a sprayer that contained 2, 4-D.

Curly top also causes curled leaves. The intensity of the disease varies and fortunately, this year the problem is not severe. Plants develop yellow leaves with purple veins along with the curled leaves. The fruit ripens at the size it was when the disease developed and is worthless as it has a strong, insipid flavor.

Tomatoes are not affected by many insects but a few cause considerable damage. Flea beetles are shiny black beetles about 1/16" in length. They attack the plants and eat many small holes in the leaves. Sprays are necessary to control them in severe cases. Tomato hornworms may reach 4 inches in length and eat foliage and fruit. The best control is hand picking the worms as they appear. Severe outbreaks or large acreages may require the use of BT (dipel or thuricide). B.T.has no harvest restrictions so it will not interfere with enjoyment of the tomatoes.

The corn earworm (called tomato fruit worm on tomatoes) occasionally attacks tomato fruits. Because the problem is not usually severe, no sprays are recommended.

Spider mites are not an insect but they still cause problems. The tiny mites are barely visible to the naked eye. They cause small yellow specks on the tomato leaves and often form very fine webs. Controls for mites on tomatoes include nicotine sulfate and insecticidal soaps. Sprays must be applied to the bottom side of the leaf.

True diseases on tomatoes also cause serious problems. Unlike the physiological conditions mentioned at the first of the article, fungi cause these.

Early blight causes round, dark brown spots usually on the lower leaves. The concentric rings within the spots give a target like appearance. The tissue surrounding the spots turns yellow and if the spots become numerous the leaves wither and dry. Control by spraying fixed coppers, or chlorothalonil (daconil). Tomato leaf diseases are only problems if the plants are overwatered.

Tomatoes are susceptible to verticillium or fusarium. The fungus is inside the plant and cannot be controlled by sprays. Affected plants show discoloration and streaking in the interior of the stem as the fungus plugs off the water conducting tissue thereby causing the wilt symptom. Most garden soils are infested with the disease and rotation is not practical because the disease survives in the soil for up to 20 years. The only practical control is resistant varieties, listed as VF. Resistance unfortunately does not immunity and plants still die.

Even though tomatoes do suffer from some problems, there is certainly no comparison between a homegrown tomato and the hard, flavorless supermarket varieties. Whether you enjoy them in salads, on BLT sandwiches or fresh from the garden there is really no substitute, and the flavor and enjoyment make the battle with the pests worthwhile.

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