Photo found on Flickr, courtesy of D Sharon Pruitt.
If you’re a gardener who loves tomatoes, you know the luscious pleasure of picking a ripe tomato and eating it, with juice running down your chin. If you’re a gardener who grows tomatoes, you know that tomatoes are susceptible to a slew of problems. You know the challenge and reward of solving these problems.
But before you can figure out what to do about a problem with your tomato plants, you need to understand what the problem is. In this article we touch on some of the common problems and practical solutions.
Tomatoes are susceptible to fusarium and verticillium, two soil-borne fungal diseases that cause brown discoloration of the stems. Once a tomato plant gets either of these fungal diseases it’s too late to restore it to health. But you can prevent an attack of fusarium or verticillium by buying resistant seeds or plants; they’ll be labeled VFN-resistant.
Rotate crops and don’t plant tomatoes, potatoes, or peppers in the same place for three to four years. Be sure to remove and destroy any diseased plants or plant parts—don’t toss them in the compost.
In humid climates early blight, another fungal disease, attacks tomatoes. Dark spots in concentric rings usually start on the lower, older leaves. Affected leaves then turn yellow and drop off, leaving the fruits exposed to the sun, which can cause sunscald, which in turn results in lesions to the skin that can become infected with mold.
The best strategy to prevent early blight is to make sure the plants are spaced generously to increase air circulation. Keep leaves dry and off the ground. Avoid overheat watering and working in the garden when the leaves are wet. If you see diseased leaves, remove them to prevent spread of infection.
The tobacco mosaic virus causes leaves to crinkle and become mottled in color. Tomatoes look brown on the inside. The virus is spread through contact with tobacco, so smokers should wash their hands thoroughly before working in the garden. Again, no cure. Destroy infected plants. Tomato mosaic virus (TMV) produces a greenish-yellow mottling and stunting. Use TMV-resistant varieties.
A variety of bacterial diseases affect tomatoes. Crop rotation and resistant varieties helps prevent the spread of a number of bacterial problems.
Tomato Insect Pests
Various insects affect tomato plants and fruit. Check with your agricultural extension office to find out which pests are most problematic in your area.
Tomato hornworms are large, distinctive, green caterpillars that eat the leaves at the top of the plant. Even though they are three to four inches long, their green coloration gives them a good camouflage. Pick them off if you see them. If the problem gets out of hand, use bacillus thuringiensis (BT) for an organic control.
Aphids suck the juices out of the undersides of the leaves. They produce a sticky substance called honeydew that can attract even more problems. Spraying with insecticidal soap usually takes care of aphid infestations. Like aphids, psyllids are small insects that suck plant juices and can be controlled with insecticidal soap.
Cutworms cut off small plants near the soil surface. Home gardeners can discourage cutworms by placing collars around young plants. Planting later in spring after the caterpillars have finished feeding is another way to work around this destructive pest.
Other Tomato Problems
Blossom end rot causes a watery spot at the blossom end of the fruit that turns into a sunken, black wound. Lack of calcium due to water stress or high levels of nitrogen can produce blossom end rot. The best way to keep the problem at bay is to use mulch to preserve soil moisture. You can also have a soil test done, which will tell you how much nitrogen (if any) to apply to the soil.
Cracks that radiate from the stem scar and radial cracks around the fruit stem expose the tomatoes to fungal diseases. To prevent cracking mulch around the plants to retain moisture and plant varieties that resist cracking under the environmental conditions in your location.
During cool, rainy weather lower leaves may curl or roll and become leathery. Leaf curl, also called leaf roll, does not affect plant growth and requires no treatment.
Herbicides can damage the leaves and fruit of tomato plants. Herbicides can spread to the garden when applied to nearby lawns or from using grass clippings from herbicide-treated lawns as mulch or in compost.
Volumes have been written on tomato problems. In general, planting the right varieties for your location, feeding and watering properly, and watching for pests are good ways to prevent many troubles. Again, do not treat until you know what’s causing the problem.
For more information about specific problems and treatments, check out these websites:
Pictures of tomato disease and insect problems from Texas A & M Extension help with identification and control.
More photos and control recommendations, from the Colorado Cooperative Extension.
Video on common tomato problems and solutions from University of Nebraska Extension.
Tomato Growing Tips is a site completely devoted to tomato gardening, with a huge section on pests and diseases.
Lynne Lamstein gardens in Maine and Florida and is currently working on a sustainable landscape. She has a degree in ornamental horticulture from Temple University.