Tomato Plant Diseases

Septoria Leaf Spot on Tomato Leaves and Stems
Although it is called Septoria leaf spot, the disease can also infect the stems, blossoms and other parts of the tomato plant. Photo: Paul Bachi, University of Kentucky Research and Education Center, Bugwood.org

Growing fresh tomatoes is one of the true joys of the vegetable gardener. But tomatoes can suffer from all kinds of diseases and pests. Problems growing tomatoes are often the result of weather conditions. This is something that is out of the gardener's control. However, if you know your area is prone to a certain disease, you should look for varieties that are listed as resistant. Your local Cooperative Extension Service should be able to help you there.

Tomato diseases are rarely fatal if the proper management is employed. It is important to catch any tomato 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. Here are some common tomato diseases, their symptoms and what to do if tomato diseases threaten your home vegetable garden.

Tomato Diseases - Foliage

Early Blight

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

Symptoms: Dark spots with concentric rings develop on older leaves first. The surrounding leaf area may turn yellow. Affected leaves may die prematurely, exposing the fruits to sun scald.

Management: Early Blight fungus overwinters in plant residue and is soil-borne. It can also come in on transplants. Remove affected plants and thoroughly clean fall garden debris. Wet weather and stressed plants increase the likelihood of attack.

Copper and/or sulfur sprays can prevent further development of the fungus. The biofungicide Serenade® lessens problems.

Gray Leaf Spot

Gray Leaf Spot affects only the leaves of tomatoes, starting with the oldest leaves.

Symptoms: Small, dark spots that can be seen on both the top and bottom surfaces of the leaves.

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 will dry and drop. Fruit production is inhibited.

Management: Warm, moist conditions worsen gray leaf spot problems. Remove all affected plants and fall garden debris. Select resistant varieties. 

Late Blight

Late blight affects both the leaves and fruit of tomatoes. Late Blight is the disease responsible for the Irish Potato Famine. Late Blight spreads rapidly. Cool, wet weather encourages the development of the fungus. If you suspect you have Late Blight, contact your Local Extension Service for definite ID.

Symptoms: Greasy looking, irregularly shaped gray spots 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.

Management: Copper sprays offer some control. Serenade® works best as a deterrent, rather than a cure.

The Late Blight fungus can overwinter in frost-free areas. Since it spreads to potatoes, it also overwinters in potato debris and seed, even in colder areas.

Remove all debris and don't save seed potatoes. More info and photo

Septoria Leaf Spot

Septoria Leaf Spot is sometimes mistaken for Late Blight.

Symptoms: The papery patches on the leaves develop tiny, dark specks inside them. Older leaves are affected first.

Management: Copper sprays and Serenade® are somewhat effective at halting the spread of symptoms. More info and photos

Southern Blight

Southern Blight manifests as a white mold growing on the stem near the soil line.

Symptoms: Dark, round spots will appear on the lower stem and both the outer and inner stem will become discolored. Southern Blight fungus girdles the tomato stem and prevents the plant from taking up water and nutrients. Young plants may collapse at the soil line.

Management: Crop rotation seems to help. There has also been some evidence that extra calcium and the use of fertilizers containing ammonium offer some protection.

Get  more info about control from Minnesota Extension Service.

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 it 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: Wilting during the hottest part of the day and recovering at night, yellowing and eventually browning between the leaf veins starting with the older, lower leaves and discoloration inside the stems. Verticillium Wilt inhibits the plant's ability to take in water and nutrients and will eventually kill the plant. Verticillium wilt is more pronounced in cool weather. (Verticillium wilt can often be confused with Fusarium wilt.)

Management: Remove affected plants and choose resistant varieties. More info and photo from Vegetable MD Online

Read more about tomato diseases that affect the fruit.


Tomato Diseases - Fruit

Anthracnose

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

Symptoms: Small, round, sunken spots appear on the fruit. The spots will 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 Early Blight spots or dying leaves. Wet weather 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" of leaves, to avoid contact with the soil. Don't water the leaves, just the base of the plant. More info and photo from Cornell University Cooperative Extension

Bacterial Speck

There are several bacterial problems that affect tomatoes including Bacterial Speck.

Symptoms: Tiny, raised, dark spots, usually with a white border.

Management: Copper fungicide at first signs of symptoms. ​

Blossom End Rot

Blossom End Rot is as good a description as any.

Symptoms: Dark brown/black spots develop at the blossom end of the fruit and enlarge as the fruit rots. Management: Generally attributed to a lack of calcium during fruit set. This could be caused by too much high nitrogen fertilizer or uneven watering, resulting in fluctuations of nutrient availability.

Management: Remove affected fruit and provide regular, deep waterings. More info and photo

Buckeye Rot

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

Symptoms: Buckeye Rot is similar to Blossom End Rot, except on green fruit. On ripened fruit, the rotting area will appear water-soaked, but not dark in color. The rot develops on the area of the fruit that touches the soil. The spot will enlarge and develop concentric rings that resemble a buckeye. The affected area is smooth, distinguishing it from Late Blight, which has a rough surface.

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

Gray Wall 

Gray Wall is essentially a ripening problem.

Symptoms: The green fruits may have a gray cast or gray blotches. Ripe fruit will have green or brown areas on the inside of the fruit.

Management: Good growing conditions will prevent gray wall. Make sure plants aren't heavily shaded, 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.More info and photo from Cornell University Cooperative Extension