Speck and Spot are bacterial diseases with similar symptoms, causing small black specks or patches on leaves, stems, and fruit. They can be distinguished from Early Blight by the water‐soaked appearance other spots, and the fact that the spots don't cross the larger veins. Like Early Blight, these bacterial diseases are spread by water, and they can overwinter in soil and on debris from the previous season.
Control/Pest: Prevent and control these diseases as you would Early Blight, above. Bacterial spots stop spreading in dry, warm weather. Chemical controls are usually not needed.
Early Blight is a common leaf spot caused by the fungus Alternaria solani. Dark brown spots with broad yellow haloes appear on the leaves, and concentric rings can be found in the spots under bright light.
Stems and fruit can also be infected. It often progresses from the bottom of the plant upward. Cool humid weather or overhead irrigation encourage Early Blight, which is spread by splashing water and germinates on moist leaves.
Control/Pest: Avoid getting water on the leaves whenever possible, change the locations where you plant your tomatoes, mulch well around each plant, and clear away all dead or infected plant material at the end of each season. Picking off infected leaves may slow the progression of the disease until the weather is more favourable.
Late Blight is caused by Phytophthora infestans, a fungal disease most famous for the Irish potato famine. It is just as serious in tomatoes, causing dark green to purple‐brown water‐soaked spots that grow quickly on leaves and stems. The underside of infected leaves will sometimes have whitish powdery spores. Fruit turns brown but stays firm. The fungus thrives during periods of high humidity and mild temperatures (60‐78° F). Once it gets going, it can kill a plant very rapidly and spread to other tomatoes, peppers, or potatoes.
Control / Pests: Avoid sprinkler irrigation, very dense planting, or other things which keep humidity high. Remove volunteer potatoes or tomatoes, and clean up debris at the end of the season. Mulching may help prevent initial infection.
VERTICILLIUM WILT (Verticillium dahliae) is similar to Fusarium Wilt, and it can be difficult to tell them apart, though Verticillium prefers cool temperatures rather than warmth.
Controls / Pests: Management is the same as for Fusarium Wilt; resistant varieties carry a V on the label.
Powdery Mildew can appear in late summer or fall as the nights cool, but it rarely causes much damage. Irregular yellow blotches with a faint coating of white powder form on the leaves, and eventually cause brown dead patches.
Controls / Pests: No control is necessary on mature plants, but in the case of young or severely affected plants, sulfur dust (1) provides good control.
CUTWORMS are green or brown caterpillars that curl into a C shape when disturbed. They eat young plants at the soil line at night, and can leave a healthy seedling cut off entirely and lying on the ground.
Controls / Pests: Eliminate weeds around garden beds at least two weeks before planting. Hand‐picking cutworms at night may help, or you can protect seedlings with cardboard collars or one or more toothpicks
(Inserted close and parallel to the stem).
Aphids affect tomatoes, especially vigorously growing ones.
Controls / Pests: A handful of aphids won't hurt a healthy tomato plant, but if new leaves are curling or the shoots are coated in aphids, crushing aphids by hand or blasting them off with a strong jet of water will control them.
Stinkbugs are an annoyance to tomato growers, as their feeding can cause corky white patches under the skin of ripe tomatoes. These patches don't peel easily when cooking or canning the fruit.
Controls / Pests: Hand‐pick stinkbugs or snip them with garden shears; a bucket of soapy water held under them can help, as they often drop when disturbed. Eliminate weeds around garden beds at least two weeks before planting. Insecticides are not recommended.
Snails and Slugs can be a problem, especially if plants are on or near the ground. They rarely bother foliage on mature tomatoes, but they can eat large chunks of ripening fruit if they have easy access.
Controls / Pests: Keep tomato plants and especially fruit off the ground by using cages or staking.