Insects and diseases, part II: Disease can catch up with tomatoes

Tomatoes are a favorite of America’s home gardeners. They taste great and also are good for you. What a perfect food. No fat and lots of vitamins C and A. Tomatoes were once known as “love apples” because they were thought to be an aphrodisiac, but at my age, that would be a terrible waste of a juicy, red tomato fresh-picked from the garden.

Growing tomatoes requires some TLC. Water, heat, insects and diseases cause great stress on growing tomato plants. Tomatoes are prone to a number of leaf, stem and fruit diseases that can drastically cut your home yield. Less than 10 diseases and only a handful of insect pests are responsible for the majority of tomato problems.

Here is a list of some of the more prevalent tomato disease in southeastern North Carolina and the cure:

Bacterial leafspot, canker or speck are caused by a wide range of bacteria that are generally spread on seed or transplants from water splash (from the soil). Symptoms will vary depending on which part of the plant is affected, but in general, small lesions (1/16th of an inch) will first look dark and water-soaked, and then appear brown. For control, use disease-free transplants. Spray with copper fungicides at first appearance of disease and repeat at 7-10 day intervals.

Early blight, a common killer of home tomatoes, is caused by a fungus—irregular brown spots that are 1/4-inch in diameter with miniature “bull’s-eye spots” appearing first on lower leaves. The disease will often move from the lower to upper leaves. Fruit will often develop dark brown sunken lesions near the stem. Spray one of the fungicides labeled for tomatoes and follow label directions.

Late blight is a serious disease of tomatoes caused by the same pathogen (Phytophthorainfestans) that caused the great potato famine in Ireland in the late 1840s. Dark water-soaked patches appear on leaves during humid, wet weather that eventually cause the leaves to shrivel and brown until all leaves have fallen. The fungus is most active during cool nights (45-60-degrees) and warm days (70-85-degrees). Use the same fungicide and controls as used for early blight.

Leafspots are caused by fungi. Septoria is perhaps the most common. Follow the same procedures as outlined for early blight and late blight.

Verticillium wilt and fusarium wilt are the fungal equivalents of bacterial wilt and symptoms are somewhat similar. The main stem of the tomato will have brown streaks just inside the stem when sliced lengthwise. Plant genetically resistant varieties. For example, VFN used in the name of a tomato means that a variety is resistant to verticillium wilt (V), fusarium wilt (F), and root-knot nematodes (N).

Southern bacteria wilt is a terrible bacterial disease that clogs the water-conducting vessels in the plant stem. Plants with this disease show gradual stem wilt and eventually die. No pesticide is really effective. Use genetically resistant plant varieties to verticillium wilt (V), fusarium wilt (F), and root-knot nematodes (N).

Viruses, like tobacco mosaic virus (TMV) and cucumber mosaic virus, cause older leaves to be mottled yellow and green, curled and deformed. Viruses are spread by insects, on the hands of tobacco smokers and when infected plant juices come in contact with non-infected plants. Immediately discard infected plants to prevent further infection in the garden, as there is no cure. Use genetically resistant varieties if available when planting your garden.

Blossom-end rot is a physiological disease of the fruit that causes the blossom end of the tomato to have a dark brown, leathery rot. The problem is caused by a calcium deficiency and is often induced by hot, dry weather, poor soil fertility or a combination of factors. Lime according to soil test recommendations, irrigate plants regularly in dry weather and spray to drip with one-half ounce of either (but not both) calcium chloride or calcium nitrate in one gallon of water weekly after the first appearance of the disease.

Nematodes are terrible on tomatoes in sandy soils. No pesticides are available to the homeowner that does a respectable job of nematode control in the garden. Incorporate lots of organic matter into your garden (manures, mulches, etc.). Research has shown high chitin (e.g. the material making up shrimp shells, crab shells and fish scales) containing compost inhibits nematode populations. Use varieties of tomatoes that have genetic resistance to nematodes (see verticillium wilt).

Send your gardening questions or comments to: Brunswick County Master Gardener Column, P.O. Box 109, Bolivia, NC 28422, or call 253-2610. Enclose a self-addressed stamped envelope if requesting information or a reply. Answers may be printed in this column.