Common Tomato Diseases Every Gardener Should Know – and How to Treat Them So You Still Get a Healthy Harvest

Tomatoes are a staple of the home vegetable garden. These tasty fruits (yes, fruits!) are generally easy to grow, but tomato diseases can cause major consternation to gardeners. When left untreated, they can diminish harvests and even kill plants. That's why learning how to identify and control common tomato diseases is so important.

The first step in fighting tomato diseases is identifying what they are. Illnesses that occur when growing tomatoes could be infectious diseases caused by bacteria, fungi, viruses, or nematodes. They could also be non-infectious diseases caused by physical, chemical, environmental, or other factors.

No matter what issue is ailing your plants, there's a way to treat your sick tomatoes and still get a good harvest – as long as long as you act fast! I'll help you learn to identify and control common tomato diseases so you can keep picking tasty tomatoes all season.

Common Tomato Diseases

A variety of factors – from harmful pathogens to environmental issues – can cause tomato diseases. These can result in everything from cosmetic damage to eventual death of the plant.

Learning the symptoms of common tomato diseases will help you manage issues and diseases that may crop up when growing tomatoes. The key is catching problems early and identifying the exact cause so you can provide the proper treatment.

There are a few different categories of common plant diseases that impact tomatoes. These include fungal, bacterial, and viral diseases as well as environmental issues that can cause problems, too. I'll break down the most common diseases in each category and teach you how to treat them.

Fungal Diseases

Fungal diseases are common in tomato plants, but they're often easy to avoid and treat. Here are the most typical problems to watch out for and how to treat them.

1. Fusarium Wilt

Fusarium wilt is a fungal disease that disrupts the uptake of water. Initial symptoms are yellowing of the lower leaves followed by wilting and leaf drop. As the disease progresses it moves up the stem of the plant, killing all the foliage. With no way to photosynthesize, the plant eventually dies.

This fungus overwinters in soil and is also spread through seeds. It is encouraged and spread by warm temperatures between 80-90°F (27-32°C), sandy soil, air movement from wind, water, and dirty garden tools.

Crop rotation along with the use of disease-resistant seeds, like these 'Magic Mountain' tomato seeds from Burpee, can limit the progression of fusarium wilt. Otherwise there is no cure for the disease. Bag up and dispose or burn infected plants. Do not put infected plants in the compost pile.

Verticillium wilt presents with the same leaf symptom, but attacks both sides of the plant at once. Many hybrids are resistant to these two tomato plant diseases. Look for the abbreviations "F" and "V" on seed packets to tell if plants are resistant to fusarium and verticillium wilt.

2. Anthracnose

Anthracnose is a common disease in tomato plants. It shows up as small circular, bruised spots on the skin that invite other fungi to infect the interior of the fruit.

Anthracnose in tomatoes is spread by high humidity and frequent rainfall as well as overhead watering. Always water plants at the base to prevent diseases. Pathogens in the soil can splash back up onto plants and spread disease quickly. Setting up an easy drip irrigation kit, like this one from Home Depot that our Content Editor Laura swears by, can help prevent anthracnose and other tomato diseases that spread from overhead watering.

You can use a fungicide spray, like this one from Amazon, to slow the progression of anthracnose, but ultimately, it is a losing battle. Thankfully, though, you can still eat tomatoes impacted by anthracnose. Just cut out any lesions first.

At the end of the season, be sure to clear out affected tomato plants to prevent overwintering the disease. Then next year, plant tomatoes in a different part of the garden to remove any chance of the disease impacting your new crop.

3. Blights

There are a few common types of blight that impact tomato plants. The three most prevalent are early blight, late blight, and Southern blight.

Early blight begins as small black lesions on the leaves and soon forms concentric rings like a target. This tomato disease's telltale mark is found at the stem end of the fruit, which turns black.

Late blight usually occurs when late-season temperatures are cool and dew is heavy. It appears as dark water-soaked spots on the leaves. The fully formed fruit rots on the vine before ripens.

Southern blight is caused by the pathogen Sclerotium rolfsii, which has a huge host range of more than 200 species. This devastating disease rapidly results in an entire tomato plant wilting.

Southern blight begins as water-soaked lesions on the stem at the soil line. The stem lesions are covered with white mold accompanied by brown sclerotia. As the disease progresses, the lesions brown, grow, and eventually girdle the stem.

This disease is fostered by high humidity, moist soil, and hot temperatures between 85 and 95°F. The sclerotia germinate in the soil and then colonize near the soil surface.

Because of the large number of sclerotia in the soil, Southern blight is difficult to control. Crop rotation reduces the incidence of the disease. Using fungicides can also help to control this disease.

In the case of any fungal disease, removing any plant debris from the site can help reduce the harmful pathogens. Keeping the area weed free can help, too. Always sanitize garden equipment as well and rotate nightshade crops each year for 3-4 years to prevent diseases impacting other vegetables in the same family.

4. Molds & Mildews

Powdery mildew should be included in any list of tomato diseases. This disease is often found where plants are closely planted and air circulation is poor. It looks like a white powdery substance on the leaves.

Thankfully, powdery mildew is more of a cosmetic concern than a life-threatening issue for tomatoes. Prevent powdery mildew by using drip irrigation instead of overhead watering and spacing tomatoes so there is good airflow between plants.

Tomato leaf mold is more common among tomatoes grown in greenhouses or high tunnels. The high humidity, heat, and lack of airflow cause this problem. Light green to yellowish spots appear on leaves, then they turn bright yellow. Tomato leaves start curling, then wither and fall off the plant. Use a fungicide spray, like this one from Bonide, to treat mold and mildew on tomatoes.

Bacterial Diseases

Bacterial diseases are caused by microscopic, single-celled organisms that multiply quickly. They are usually transmitted via contaminated seeds or transplants. They can spread in the rain, wind, from equipment, people, insects, or pets. Here are the most common types to watch out for.

1. Bacterial Leaf Spot

Bacterial leaf spot survives on plant debris and seeds and is promoted by wet temperatures from 75-85°F. It appears as dark brown, greasy-looking spots on leaves, fruit, or stems of the plant at any stage of growth. Heavily spotted areas become chlorotic followed by the rapid death of leaves from lower to higher on the plant.

Spots on green fruit are raised, scabby, and dark brown. On ripe fruit, they become more sunken. These leaf spots look very similar to those caused by another bacterial disease called tomato bacterial speck as well as the fungal disease septoria leaf spot.

Bacterial speck affects both leaves and green fruit causing small dark brown spots with a yellow halo. Like bacterial spot, bacterial speck is fostered by wet conditions but cooler temperatures of 55-77°F.

Control for both diseases is the same. Use certified clean seeds and transplants, preferably ones that are disease-resistant, like these 'Cherokee Purple' tomato seeds from Burpee.

Remove any diseased plant debris, rotate crops, and use drip irrigation to reduce the incidence of bacterial diseases. Also, a weekly application of a mix of copper and fungicide, like this spray from Amazon, can reduce the incidence of the disease and increase yields.

2. Bacterial Canker & Wilt

Bacterial canker and wilt are two other bacterial diseases known to afflict tomatoes. Tomato bacterial canker produces a number of symptoms making it difficult to diagnose. However, bacterial wilt results in rapid wilting of the entire plant and coincides with brown decay inside the stems of the plant. Bacterial wilt is easy to diagnose. When the stem is cut open, it disgorges a slimy, milky stream.

The bacterial canker pathogen is transmitted by seeds or transplants and can survive for a time on plant debris, nightshade weeds, or volunteer tomato plants. It is spread through water splash, dirty garden equipment, and activity around the plants.

Use certified clean seeds and transplants to control both bacterial diseases. Rotate crops. Bactericides are not effective. There is no cure for either of these diseases. Remove and destroy infected plants immediately.

Viral Diseases

Viral diseases in tomatoes can be difficult to treat. The best control method, as with any plant problem, is prevention. Watch for the signs of these common diseases in tomato plants to keep them at bay.

1. Curly Top Virus

Curly top virus, also called western yellows disease, is caused by the beet curly top virus. A severe disease of tomatoes, the virus can spread great distances and is transmitted by the beet leafhopper, which can infect 300 different host plants. Interestingly, leafhoppers do not feed on tomatoes, so their infection is generally solitary, rather than affecting an entire crop.

Symptoms begin as curly, pale green upper leaves. As the disease progresses, all the foliage becomes twisted and pale. Leaves also become thick with obvious purple veining. Early infection of tomatoes will kill the plant.

To control curly top virus in tomatoes, you have to reduce the numbers of leafhoppers attracted to them. You can do this by intercropping, varying the crop pattern, planting tomatoes in shaded areas, or by covering the fruit with row covers, which you can buy on Amazon. There are no resistant varieties and insecticides are ineffective against this disease.

2. Tobacco Mosaic Virus

Tobacco mosaic virus is a minor viral disease, due to the ready availability of resistant varieties. It is spread by mechanical and human interactions with plants.

Symptoms vary depending upon the strain of virus, but generally present as small, curled and mottled areas on foliage. Fruit is usually unaffected, although in some cases, mosaic patterns may be present.

There is no cure for tobacco mosaic virus, but again, there are many resistant varieties. Botanical Interests has a wide variety of disease-resistant tomato seeds you can grow in your garden. Wash hands well after using tobacco products and before handling plants.

3. Tomato Spotted Wilt

Tomato spotted wilt is the result of two viruses that are spread by thrips in the greenhouse or field. They most commonly affect tomatoes and peppers. Fruit loss can be a major issue in areas of high infection, especially early in fruit development.

Symptoms may vary but generally appear as brown spotting of young leaves, stunted growth, and streaking of stems. Ringspots may also be present on foliage. Because symptoms of the disease vary, definitive diagnosis can be made through your local extension office.

Management consists of the use of healthy transplants in the field. In the greenhouse, avoid cultivating veggie transplants along with ornamentals and enclose the structure with thrip proof fine meshed screens. Also inspect any incoming plants for signs of thrip infestation.

Controlling the thrip population with insecticides is ineffective. Plant resistant tomato varieties. Remove and destroy infected plants.

4. Alfalfa Mosaic Virus

Alfalfa mosaic is a viral disease with a large host range. In the case of tomatoes, the disease is transmitted by aphids to healthy plants or mechanically. This disease is most commonly present when tomatoes are cultivated near infected alfalfa fields.

Alfalfa mosaic presents as a yellow mosaic pattern on newly emerging foliage combined with extensive browning and splitting of the fruit. This disease can be prevented by the removal of infected plants and not planting tomatoes near alfalfa fields.

Environmental Issues

• Temperature, humidity, soil health, and fertilizing can all affect the health of your tomatoes. Temperatures below 50°F and above 90°F can result in tomato blossom drop and lack of pollination. High humidity makes pollination difficult.
• Arid soils can result in fruit drop and salt rich soil can damage cells and thwart water uptake.
• Too much nitrogen fosters foliage but not fruit growth. In the presence of developing fruit, excess nitrogen results in cracking.
• Catfacing is another issue caused by environmental factors. Catfacing is when the fruit is physiologically damaged resulting in cavities forming at the blossom end of the fruit.
• Herbicide drift, water stress, lack of or too many nutrients, frost injury, and sunscald are also environmental stressors that can damage tomato plants.

Frequently Asked Questions