Save Your Tomato Plants From These Common Diseases

Close up of beautiful tomatoes ready to be harvested
Sol de Zuasnabar Brebbia / Getty Images

Growing fresh tomatoes is one of the true joys of the vegetable gardener; however, tomatoes can suffer from all kinds of diseases and pests. Causes are often related to weather conditions, which of course can't be controlled. If you know your area is prone to a certain disease, you should look for varieties that are listed as resistant (ask your local cooperative extension service for recommendations.)

Tomato diseases can be fatal unless you take management steps in a timely manner. It is important to catch any disease early, before it spreads to all of your tomato plants and possibly other plants in the same family, such as potatoes, eggplants, and peppers. Some diseases affect the foliage, while others attack the fruit.

Early Blight

Early blight can affect the foliage, stems, and fruit of tomatoes.

Symptoms: Dark spots with concentric rings develop on older leaves first that touch infected soil. The surrounding leaf area may turn yellow. Affected leaves may die prematurely, exposing the fruits to sunscald. It also infects stems and fruit, presenting as black leathery spots on fruit.

Management: Early blight fungus overwinters in plant residue and is soil-borne. It can also come in on transplants and survives in seeds of infected plants. Remove affected plants and thoroughly clean fall garden debris. Do not compost affected plants. Wet weather and stressed plants increase the likelihood of an attack. Copper and/or sulfur sprays can prevent further development of the fungus. The biofungicide Serenade® helps to minimize problems with early blight. In areas impacted by early blight, look for cultivars that are resistant to the disease--the tag often shows "Resistant to EB (Early Blight)."

Stemphylium Gray Leaf Spot

Gray leaf spot affects mainly the leaves of tomatoes, starting with the oldest leaves, although it can also infect the stems on the plant. It does not infect the fruit, although the disease can be harbored in the seeds of the infected plant.

Symptoms: Small, dark spots that can be seen on both the top and bottom surfaces of the leaves. The brown spots are surrounded by a yellow halo. The spots enlarge and turn a grayish brown. Eventually, the centers of the spots crack and fall out. Surrounding leaf areas will turn yellow and the leaves dry out and drop. Fruit production is inhibited.

Management: Warm, moist conditions worsen gray leaf spot problems. Remove all affected plants and fall garden debris. Do not compost infected plants. Cherry and grape tomato plants are most often impacted. Select resistant varieties. Rotate crops to avoid planting in infected soil.

Late Blight

Late blight affects the leaves, stems, and fruit of tomatoes. A strain of late blight is the disease responsible for the Irish Potato Famine. Late blight spreads rapidly. Cool, wet weather encourages the development of the disease. Late blight is caused by the oomycete Phytophthora infestans, which is not a true fungus but still causes devastation to plants. If you suspect you have late blight, contact your local extension service for positive identification. There are actually many strains of late blight.

Symptoms: Greasy-looking, irregularly shaped dark brown blotches with green gray edges on leaves. A ring of white mold can develop around the spots, especially in wet weather. The spots eventually turn dry and papery. Blackened areas may appear on the stems. The fruit also develops large, irregularly shaped, greasy gray spots and can turn mushy from a secondary bacterial infection.

Management: Late blight can decimate a tomato crop. Copper sprays offer some control. Serenade® works best as a deterrent, rather than a cure. Late blight can overwinter in soil. Since strains can spread to potatoes, it also overwinters in potato debris and seed, even in colder areas. Remove all debris and don't save seed potatoes. Rotate crops to prevent infections the following year.

Blight in Tomato
FerhatMatt / Getty Images

Septoria Leaf Spot

Septoria leaf spot is sometimes mistaken for late blight. It's a fungal infection that affects leaves but not the fruit.

Symptoms: The infection appears as small, dark spots that enlarge to 1/4-inch diameter. The spot develops a tan or gray center, and the leaves eventually wilt and fall off. Older leaves are affected first.

Management: Copper sprays and Serenade® are somewhat effective at halting the spread of symptoms. Remove infected leaves to prevent the spread of spores to other leaves, as water splashing on the leaves helps transmit the disease.

Southern Blight

Southern blight manifests as a white mold growing on the stem near the soil line. In not only affects tomatoes, but it also impacts peppers, beans, cantaloupes, carrots, potatoes, watermelon, and peanuts, among others.

Symptoms: Dark, round spots appear on the lower stem near the soil line, and both the outer and inner stem become discolored. Southern blight fungus, Athelia rolfsii, girdles the tomato stem and prevents the plant from taking up water and nutrients. Young plants may collapse at the soil line. Fruit near the stem can become infected as well.

Management: Use a fungicide as a preventative. The fungus remains in the soil for several years. Dispose of infected plants and plant debris--do not compost. Rotate crops.

Rotten Moldy Tomato
DIMUSE / Getty Images

Verticillium Wilt

This name can be misleading, as sometimes the leaves will turn yellow, dry up, and never appear to wilt. Verticillium wilt is caused by a soil-borne fungus and can affect many different vegetables. The fungus can persist in the soil for many years, so crop rotation and selection of resistant varieties is crucial.

Symptoms: Yellow blotches on lower leaves that eventually turn into brown dead spots. Symptoms start on older, lower leaves and move upward. Verticillium wilt stunts the plant, producing smaller fruits that may suffer from sunscald. Verticillium wilt is most pronounced in cool weather. Note: Verticillium wilt can often be confused with fusarium wilt.

Management: Remove affected plants and choose resistant varieties. Look for a "V" on the plant tag. Rotate crops.

Anthracnose

Anthracnose is a very common fungus that causes tomato fruit to rot.

Symptoms: Small, round, sunken spots appear on the fruit. The spots increase in size and darken in the center. Several spots may merge as they enlarge. The fungus is often splashed onto the fruit from the soil. It can also take hold on spots of early blight or on dying leaves. Wet weather and poorly drained soils encourages the development of anthracnose. Overripe tomatoes that come in contact with wet soil are especially susceptible.

Management: Copper sprays offer some resistance. Remove the lower 12 inches of leaves to prevent contact with the soil. Water only the base of the plant, not the leaves. Spores overwinter in soil, so practice crop rotation.

Bacterial Speck

Bacterial speck is one of several bacterial problems that affect tomatoes. Caused by the bacteria Pseudomonas syringae pv. tomato, it reduces yields. There's no cure for the plants once infected. It's most prevalent in cool, moist weather.

Symptoms: Tiny, dark spots, usually with a yellow border, on fruit and leaves. The spots may be raised, flat, or sunken.

Management: Avoid splashing water on leaves. The disease can be transmitted to healthy plants by water, hands, and garden tools. Remove affected plants and debris--do not compost. Rotate crops.

Blossom End Rot

Blossom end rot is generally attributed to a lack of calcium availability during fruit set. This could be caused by too much high-nitrogen fertilizer or uneven watering, resulting in fluctuations in nutrient availability. It's a physiological disorder, not a disease, but it still results in loss of fruit.

Symptoms: Dark brown/black spots develop at the blossom end of the fruit and enlarge as the fruit rots. The spots look water-soaked.

Management: Remove affected fruit and provide regular, deep waterings. Add garden lime to soil to help with the uptake of water and nutrients. Use a fertilizer low in nitrogen and high in phosphorous.

Blossom end rot on beefsteak tomatoes (Solanum lycopersicum) caused by irregular watering
John Beedle / Getty Images

Buckeye Rot

Buckeye rot is more common in Southern states, especially during warm, wet periods.

Symptoms: Buckeye rot affects both green and ripe fruit. The small brown spot will enlarge and develop concentric rings that resemble a buckeye. The affected area may appear round or oblong, and the firm lesion with smooth margins becomes soft and decayed as the disease progresses.

Management: Remove affected fruit and keep future fruits from contact with the soil. Avoid surface water.

Gray Wall 

Gray wall is essentially a ripening problem. There's no known associated pathogen.

Symptoms: The green fruits may have a gray cast or flattened, gray blotches. Ripe fruit have a mottled appearance and green or brown areas on the inside of the fruit.

Management: Good growing conditions help prevent gray wall. Make sure plants are not heavily shaded and are receiving even waterings and fertilizer and that the soil is not compacted around the roots. Cool temperatures and stressed or unhealthy plants also contribute to the problem.

Article Sources
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  1. Early Blight of Tomato. University of Minnesota Extension

  2. Common Diseases of Tomatoes. Mississippi State University Extension

  3. Late Blight of Tomato. University of Maryland Extension

  4. Southern Blight of Tomato and Pepper. North Carolina State Extension

  5. Anthracnose - Vegetables. University of Maryland Extension

  6. Vegetable: Tomato, Buckeye Rot. University of Massachusette Center for Agriculture