Common Tomato Plant Diseases
Tomato plant diseases may cause you great heartache, but buying disease resistant tomatoes and taking careful precautions before planting helps immensely. Should your tomato plants fall ill, you can diagnose many tomato problems on your own just by taking note of symptoms. Not every tomato plant disease has a cure. Find out what’s causing your tomato diseases so you can either deal with it or plant more successfully next year.
General Precautions for Avoiding Tomato Diseases
You must take some general precautions to avoid tomato plant problems.
Wash your hands with antibacterial soap before gardening (and after).
Wash your garden tools frequently with mild bleach solution (10 percent bleach, 90 percent water). Dry thoroughly before storing to prevent rust.
Use your garden tools only for gardening and if you have significant problems with tomato diseases, get a separate set of tools just for tomatoes.
Wash your clothes if you’ve been doctoring tomato plants in the garden. Some tomato diseases spread by contact, and herbicide or fungicide residue on your clothes damages healthy tomato plants. Don’t forget your shoes.
Diseased plants and tomato fruits must be completely removed from the garden. Never compost infected plant matter—some of these fungi or bacteria live through the composting process. Burn diseased tomato plants if possible, or place in heavy garbage bags and send them to the landfill.
Water below the tomato plant leaves. A drip hose will keep the leaves dry which breeds many tomato plant diseases and water the garden more efficiently than an overhead sprinkler.
Herbicide use damages tomato plants and other garden vegetables so use these chemicals only as a last resort. Be careful applying herbicide to your lawn because the mist drifts on the wind. Never mulch your garden with poisoned grass clippings, and use natural methods to control weeds in the lawn.
Several of the tomato plant problems described below may be contained by rotating crops on a four year cycle. This excellent method helps keep the garden disease free, but you must not plant peppers, potatoes, eggplants, or sunflowers in the same area as tomatoes. These plants are also susceptible to tomato diseases. Try corn—it attracts tomato pests away from your tomato plants and will not play host to tomato diseases.
Tomato Leaf Roll
Causes. Tomato leaf roll isn’t a disease, and it’s not anything for a gardener to worry about. Cool weather at any point in the tomato plant’s growth cycle causes leaf roll. Rain and cloudy days contribute to this worrisome problem as well.
Symptoms. Lower leaves curl up tight and become thick and leathery. They may also appear darker green.
Solutions. Keep baby tomato plants warm until the weather is more cooperative by placing mini greenhouses or clear plastic sheets over them. Remember to remove the plastic if the sun shines for several hours or the air temperature warms up significantly; you don’t want to cook your tomato plants.
Learn more about Tomato Leaf Roll.
Alternaria (Early Tomato Blight)
Causes. Alternaria, more commonly called early blight, is caused by the fungus Alternaria solani.
Symptoms. Early tomato blight attacks the stems and the leaves. Stems appear brown at the soil line. This is known as collar rot. Black or brown spots appear on the tomato plant, and lower leaves have dark concentric rings all over them. In a bad alternaria outbreak, ripening tomatoes may be affected as well.
Solutions. Early tomato blight begins to show clear signs in the hottest months of the summer. Since it’s caused by a fungus it is incredibly hard to eliminate completely, so clean the garden of all litter if plants are diseased. Rotate crops carefully and allow plenty of space between them. Sulfur dust or fungicides may be helpful if prevention doesn’t work for you.
Late Tomato Blight
Photo courtesy of photofarmer at Flickr.com.
Causes. Like Early Blight, Late Blight thrives on wet weather.
Symptoms. Evidence of the fungus includes moldy leaves, grey spots on the leaves and blackened stems. Tomatoes can develop large grey spots that are oily or slimy in nature.
Solutions. Infected plants cannot be effectively treated and should be removed, but a fungicide can help prevent further spread of the disease.
Septoria Leaf Spot (Tomato Leaf Blight)
Causes. Tomato leaf blight is caused by garden soil infected with Septoria lycopersici fungus splashing onto the leaves.
Symptoms. Septoria shows up as crinkly edges and brown spots all over the leaves. It looks like a case of freckles gone terribly wrong. Spots have light colored centers and dark margins.
Solutions. Mulch prevents most splashing so place two or three inches of mulch around the perimeter of each tomato plant. If you manually or automatically water your garden, do it gently in the morning so the leaves have time to dry before nightfall.
Causes. Southern tomato blight is caused by the fungus Sclerotium rolfsii which enjoys living in the soil in warm, wet states.
Symptoms. If your tomato plants are attacked by southern blight, you’ll know it: they’ll be covered with white fungus. Small brown growths appear along with the fuzzy, icky covering, and the stems rot at the soil line. Your tomato plants wilt and die in short order.
Solutions. An application of calcium nitrate at transplanting time may help keep southern blight from forming. Once it’s established, the only thing to do is dig out and destroy infected plants and rotate crops carefully. Southern blight loves rotting plant debris, moist environments, and heat, so keep your garden clean.
Tobacco Mosaic Virus
Causes. Tobacco mosaic infection is caused by the tobacco mosaic virus. The only way your tomato plants get it is by direct contact with tobacco products. If you’re a smoker, wash your hands with antibacterial soap, wear fresh clothes into the garden, and wash tools with a mild bleach solution. If you buy starters from a greenhouse, make sure all the employees practice good hand washing.
Symptoms. When a tomato catches tobacco mosaic virus the plant’s leaves crinkle and look stunted, and they look as though insects have attacked. One way to tell the difference between tobacco mosaic virus and insect infestation is that the leaves are lacy from the inside of the plant outward with TMV. Insects usually attack from the outside in.
Solutions. Some tomato varieties are resistant to TMV, so choose plants or seeds labeled with a T or VFNT. Remove tobacco mosaic infected tomato plants.
Tomato Spotted Wilt Virus (TSWV)
Causes. Tomato spotted wilt virus sounds scary, and it can cause complete destruction of your tomato plants. TSWV is spread by thrips, tiny transparent flying insects. A similar virus, impatiens necrotic spot virus (INSV), spreads to tomato plants from diseased impatiens or other ornamental flowers.
Symptoms. Dark canker spots show up on the leaves and gradually spread to the stems, and leaves turn a bronze color before they drop to the ground. The leaves appear stiff and dry. Tomato spotted wilt virus also shows up in the tomato fruits themselves as large yellow spots or rings.
Solutions. There is no cure for TSWV, unfortunately, so prevention is important. Remove infected plants and tomatoes from the garden and don’t compost. Thrips love weeds so keep the weeds in the garden down and mow around garden borders. Certain varieties of tomato seeds and plants are TSWV free and virus resistant, so look for those.
Vascular Wilt Disease
Causes. Vascular wilt disease is caused by Verticillium albo-atrum and Fusarium oxysporum fungi that live in your garden soil. When they invade tomato stems they rob tomato plants of nutrition and the plants die.
Symptoms. Tomato plants that have caught verticillium wilt may appear to recover at night, but don’t be fooled. The leaves yellow in a V shape, handy for identifying this fungus. With fusarium wilt, your tomato plants start to die from the ground up and their leaves shrivel and yellow. Cutting a stem reveals spongy brown growths that feel slimy to the touch. In rare cases, tomato fruits are infected with fusarium wilt. Brown rings and lines appear on the inside when you cut the fruit.
Solutions. There is no cure for fungal rot so prevention is your only option. Keeping the soil’s pH at 7 stunts the growth of fungus without affecting your tomato plants. Rotate your crops on a four year cycle, and don’t plant tomatoes, peppers, and potatoes in the same spots since they’re all susceptible to vascular wilt disease. Completely remove diseased plants from the garden space. Heirloom tomatoes are most susceptible to verticillium and fusarium fungi. Choose seeds labeled “VFN” if you start your own tomatoes, or ask your greenhouse associate if starters are resistant.
Learn more about Vascular Wilts of Tomatoes. This resource gives tips on determining the difference between fusarium wilt and verticullium wilt. There’s more information on verticullium wilt below. And, here’s a link to photos of tomato fusarium wilt.
Symtoms. Though the name implies that plant leaves wilt when infected with this fungus, leaves can instead simply dry up or turn yellow in color. It is most common in cooler environments, and is a slow killer. Verticillium Wilt stops the flow of nutrients and water to the plant. Not all plants are susceptible to the disease; crop rotation is vital to eliminating any traces of the fungus that can live in soil for many years.
Solutions. Tomato plants infected with Verticillium Wilt should be removed.
Grey Leaf Spot
Causes. Grey leaf spot is a fungal disease. These spores can be passed by wind or rain, and tend to prefer moist leaves. Keep an eye out for Grey leaf spot when there is a rainy climate, heavy dews, or high humidity.
Symptoms. The leaves of tomato plants are most affected by Grey Leaf Spot. The disease is usually not fatal, but plant growth and fruit production can be severely inhibited by this fungus.
You’ll notice brown spots forming on the tomato plant leaves. Typically, the spots will grow to be about 2 millimeters and some may turn grey in the center. The lesions on the leaves can turn yellow and drop off the plant. While this fungus does not affect the fruit, the fruit can sunscald due to lack of plant leaves.
Solutions.Try moving tomatoes to a different location and planting a crop that is immune to Grey Leaf Spot in its place. Fungicides can be used as a preventative, but are useless in treating a plant with a current infection.
Learn more about Grey Leaf Spot.
Causes. This disease is caused by a fungus and can be mistaken for Blossom End Rot. This fungus can deteriorate a plant on its own, or piggy-back on another disease as well by invading previously established fungi abrasions.
Symptoms. Unlike Blossom End Rot, Anthracnose develops black, sunken lesions all over the fruit.
Solutions. Tomato plants can be shielded from infection by trimming the leaves from the lower sections of the plant to prevent contact with infected soil.
Causes. Buckeye rot fungal diseases and is indigenous to warm, moist climates.
Symptoms. Tomatoes infected with Buckeye Rot obtain light-colored, rotting spots with rings around the outer edges. The rotting area becomes watery and smooth. These spots are susceptible to other bacteria once they are fully developed.
Solutions. Fungicides are useful in preventing Buckeye Rot, but they must be applied several weeks before harvest time.
Getting Help With a Tomato Disease Diagnosis
If tomato plant diseases spring up in your garden, a knowledgeable local garden center associate or county extension agent may be able to help you diagnose tomato disease symptoms. Cut some leaves, place in a zip-top plastic bag, and bring them to the plant doctor.
While chemicals rarely help control tomato diseases, new products are being introduced to the market all the time. Ask an expert if there are solutions, and always use chemicals carefully.
Also, check out Cornell University’s Tomato Disease Identification Key. Click on the part of tomato plant showing symptoms: crown, leaves, fruit, or general health of the plant. The site shows diagnostic photos of tomato diseases for you to identify any tomato plant problems.
Want to learn more about tomato plant diseases?
The University of Colorado Extension has a good page with several photos that cover a few types of tomato diseases and pests.
Texas A&M’s Tomato Problem Solver is a great resource. It is an identification guide to common tomato problems.
Don’t forget to make sure your plant disease is a really a plant disease. Check out these pictures of mineral deficiencies in tomatoes. Sometimes they can look similar.