Aphids do little damage in small numbers. They are extremely prolific, however, and populations can rapidly build up to damaging numbers during the growing season. Damage occurs when the aphid sucks the juices from tomato leaves. Aphids feed on nearly every plant in the garden and are spread from plant to plant by wind, water, and people. Aphids can also spread other plant diseases, such as viral infections.

Blossom-end rot on tomatoes, peppers, squash, and watermelons is caused by a lack of calcium in the developing fruit. This comes from slowed growth and damaged roots, the result of any of several factors. 1. Extreme fluctuations in soil moisture, from very wet to very dry. 2. Rapid plant growth early in the season, followed by extended dry weather. 3. Excessive rains that smother root hairs. 4. Excess soil salts. 5. Cultivation too close to the plant. The first fruits are affected most severely. The disorder always starts at the blossom end, enlarging to affect up to half of the fruit. Moldy growths are from fungi or bacteria invading damaged tissue. The rotted area is unsightly, but the rest of the fruit is edible.

This plant disease is caused by a fungus (Alternaria solani) that attacks tomatoes at any stage of growth. Some leaf spotting appears early in the season, but most occurs as the fruit matures. Plants heavily loaded with fruit and those that are poorly fertilized are most susceptible to attack. Severe early blight causes partial to complete defoliation that weakens the plant, reduces the size and quality of fruit, and exposes the fruit to sunscald. Infected fruit should not be canned but can be eaten fresh if the diseased portion is removed. The spores survive in plant debris in the soil for at least a year. The fungus is most active in humid weather with a temperature range of 75° to 85°F.

This wilt disease is caused by a soil-inhabiting fungus (Fusarium oxysporum lycopersici) that infects only tomatoes. The fungus persists indefinitely on plant debris or in the soil. Fusarium is most prevalent in warm-weather areas. The disease is spread by contaminated soil, seeds, plants, and equipment. The fungus enters the plant through the roots and spreads up into the stems and leaves through water-conducting vessels in the stems. These vessels become discolored and plugged. This plugging cuts off the flow of water and nutrients to the leaves, causing leaf yellowing and wilting. Affected plants may or may not produce fruit. Fruit that is produced is usually deformed and tasteless. Many plants die.

Manduca quinquemaculata and M. sexta Hornworms feed on the fruit and foliage of tomatoes, peppers, and eggplants. Although only a few worms may be present, each worm consumes large quantities of foliage and causes extensive damage. The large gray or brown adult moth with yellow-and-white markings emerges from hibernation in late spring and drinks nectar from petunias and other garden flowers. The worms that hatch from eggs laid on the undersides of leaves feed for 3 to 4 weeks. Then they crawl into the soil and pupate, later emerging as adults to repeat the cycle. One generation occurs per year in the North and two to four in the South.

This disease affects many plants in the garden, including tomatoes, potatoes, eggplants, peppers, strawberries, and raspberries. It is caused by a soil-inhabiting fungus (Verticillium) that persists indefinitely on plant debris or in the soil. It is more prevalent in cool-weather areas. The disease is spread by contaminated seeds, soil, plants, and equipment. The fungus enters the plant through the roots and spreads into the stems and leaves through the water-conducting vessels in the stems. These vessels become discolored and plugged. Water and nutrients cannot flow to the leaves, causing the leaves to yellow and die. Affected plants may or may not produce fruit; if they do, the fruit is usually small, deformed, and tasteless. The plant is not usually killed.