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Since tomatoes are the most popular of all vegetables so they are always going to have some problems. What problem do gardeners see most frequently?
Overwatering! People have huge big plants with no tomatoes or with green fruits that never get ripe. Commercial producers water their plants once a week or sometimes even less frequently. Tomatoes have many more problems if they are overwatered.
One consequence directly related to overwatering is showing up right now. You have patiently waited for the fruit to come. Finally the tomatoes set on and start to turn red. You get the first ripe one, pick it and then discover the bottom is covered with a leathery black spot.
Blossom-end rot has struck. It appears as a light tan water-soaked spot on the blossom end of partially grown fruits. It is most prevalent on tomatoes but also affects peppers, squash and melons. The water-soaked area becomes sunken, leathery and turns brown/black in color.
Blossom-end rot is caused by calcium deficiency inside the plant. In Utah, fluctuating soil moisture, especially moisture stress, brings it on. Contributing factors are the use of excessive amounts of nitrogen fertilizer and root damage. In the eastern United States, the problem is lack of calcium in the soil.
Recommendations for eastern areas are to apply calcium to the soil. But since we have too much calcium in the soil, adding more does not help. Keep plants uniformly moist — avoid wide cycles of wet and dry. Prevent blossom-end rot by protecting the roots from injury; don't cultivate too close to the plants. Use plastic or organic mulch, as this helps provide a more uniform moisture supply.
The good news is that blossom-end rot usually affects the first clusters of tomato fruits and then is not as bad on subsequent production.
Curling tomato leaves are another frequent problem that plagues tomato growers. Although the symptom is common, it is caused by three different conditions. The older, lower leaves of some varieties curl and become stiff and leathery. The problem is more pronounced with high light intensity and hot, dry weather. Fruit is not affected by this condition and the tomatoes grow normally. Since there is nothing to do, simply forget about it.
Other causes of leaf curl are more serious. Tomatoes are very sensitive to chemical injury from 2,4-D, which is commonly used as a lawn weed killer. Exposure to 2,4-D causes distorted leaves, twisted stems, flower drop and fruit abnormalities. Don't use these products anywhere near tomatoes or when temperatures exceed 85 degrees F.
Curly top also causes curled leaves. The intensity of the disease varies, and unfortunately this year, the problem is widespread and severe. Plants develop yellow leaves with purple veins along with the curled leaves. The plants stop growing, and the fruit ripens at the size it was when the disease developed. It is worthless as it has an insipid flavor.
The disease is caused by a virus spread by the sugar beet leafhopper. This pest comes north as the deserts dry up, and it spreads the disease as it samples the plants. It does not like tomatoes, but the momentary feeding affects the plants for life. Since there is no cure for virus diseases, the plants are best removed, even though the disease is only spread by the leafhopper that passed through the area much earlier.
Look for tomato varieties that resist cracking. Fruit cracking makes the fruit less marketable and more likely to spoil. It varies with variety and, 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've 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.
Some tomatoes tend to be very misshapen on the blossom end and have large amounts of scar tissue. This symptom is known as cat facing. Cold weather at the time of blossom set intensifies the deformities, but damage from insects also causes cat facing or distortion.
Tomato hornworms are the giant of the vegetable garden. They may reach 4 inches in length and eat foliage and fruit. Occasionally they attack potatoes and eggplants and will also attack flowering tobacco. The best control is hand-picking the worms as they appear.
Most vine crops in the garden are susceptible to verticillium or fusarium wilt. 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, causing the wilt symptom.
Even though tomatoes suffer from some problems, there is certainly no comparison between those you grow and hard, flavorless supermarket varieties. Vegetables fresh from the garden have no substitute, and the flavor and enjoyment make the battle with the pests worthwhile.
