Tomato plant diseases are caused by bacteria, fungi, and viruses. The diseases can spread through the soil, water, air, infected tools, animals, and even gardeners themselves.

Spot diseases on your tomato plants sooner so you can treat plants before they are destroyed by disease and can successfully manage symptoms. Here is a three-step approach to keeping vigilant about the presence of tomato plant diseases:

1. Research the risks. Find out about tomato diseases that are prevalent in your geographic area. When possible, buy disease-resistant tomato plant varieties to avoid diseases in the first place—many hybrid tomato varieties have been specifically designed to resist certain diseases.
2. Examine plants daily. Check your tomato plants every day to be sure no disease symptoms are present or emerging.
3. Spot diseases early. Catch and treat disease quickly so your plants can recover and thrive.

Tomato diseases can affect the leaves, stems, crowns, and fruit. Here are possible disease symptoms to look for to spot potential infection.

Tomato leaves:

• dark, gray, or white spots
• yellowed or spotted/blotched foliage
• curling leaves

Tomato stems:

• softness or mushiness
• dark, gray, or discolored streaks
• mold or mildew
• stunted growth

Tomato crowns:

• malformations at the plant crown
• rotting roots

Tomato fruit:

• sunken or discolored spots
• spotted/blotched skin
• mold or mildew
• misshapen or undeveloped fruit

Make your own natural disease and pest control spray with benign materials. Mix one tablespoon of baking soda, 1/2 teaspoon of a mild dish detergent, and 2 1/2 tablespoons of olive oil in a gallon of water to make a solution that will repel all kinds of bugs, as well as a fungicide for blight and mildew on the tomato plant leaves. Shake it well in your bottle before spraying, and repeat every week for it to be continuously effective.

We’re believers in not using toxic materials in the garden—they can hurt the plants, hurt the soil, damage the environment, and harm you.

Preventive Measures to Avoid Tomato Plant Diseases

Try some of these techniques for avoiding tomato diseases in the first place:

Rotate crops regularly. Many bacteria, fungi, and viruses live in the soil for years and are just waiting to prey on your tomato plants! Minimize the likelihood of these diseases when you plant tomatoes by planting no more than once every three years in the same location.

Avoid planting other crops such as potatoes, peppers, or eggplants nearby, too. As members of the same plant family as tomatoes, these crops are susceptible to the same diseases as tomatoes and having them nearby could facilitate rapid spread of any developing disease.

Now, in a perfect gardening world, you would be able to implement a crop rotation plan that spans decades. There are some soilborne diseases that can live in the soil for up to 20 years!

Even so, it’s a good idea to switch things up from season to season. Here’s a list of vegetable crops by category. The general rule of thumb here is to plant crops from one list in the growing space of the crops in the following list in the next growing season. So, you would go from List 1 to List 2 to List 3 to List 4 and then back to List 1.

1. 1. Root, solanaceous (nightshade), and tuberous crops
      • tomatoes
      • carrots
      • celery
      • eggplant
      • parsnips
      • potatoes
      • bell peppers
      • sweet potatoes
      • taro

 

1. 1. Brassicas
      • broccoli
      • Brussels sprouts
      • cauliflower
      • kale
      • kohlrabi
      • mustard
      • radishes
      • rutabaga
      • turnips

 

1. 1. Legumes and pod crops
      • broad beans
      • lima beans
      • okra
      • peas
      • runner beans
      • snap beans

 

1. Alliums
   • bulb onions
   • garlic
   • leeks
   • oriental bunching onions
   • scallions
   • shallots
   • Welsh onions

Here’s a short example of common crop rotations:
tomatoes > corn > cabbage > peas > tomatoes > beans > root crops > squash/potatoes > onions

If you can’t do a complete crop rotation, consider alternating what you grow from one season to the next—a virtual crop rotation of sorts. With containers and raised beds, you have the option of changing out the soil, depending on what you want to grow there. Some container soil, especially, will be severely depleted of nutrients at the end of the growing season and should just be replaced.

Improve your soil composition. Before planting your tomatoes, add a good amount of compost or organic matter to improve the soil. Extra nutrients and good aeration help grow stronger plants that will resist disease and infection.

Plant disease-resistant tomato varieties. Many hybrid tomato varieties have been developed specifically to resist particular tomato diseases. You can plant disease-resistant tomato varieties to always have the healthiest plants and harvest. Tomato disease resistant codes are listed on seed packets or seedling containers in capital letters. They include:

• • V = Verticillium Wilt
    F = Fusarium Wilt
    N = Nematodes
    A = Alternaria
    T = Tobacco Mosaic Virus
    St = Stemphylium (Gray Leaf Spot)
    TSWV = Tomato Spotted Wilt Virus

Water your garden properly. Don’t underwater or overwater your tomato plants. By keeping a regular watering schedule, you’ll keep your plants vibrant and healthy. Overwatering and watering directly on the plants—instead of the preferred watering method, directly at the stem on the soil—leads to consistently wet conditions, which allows bacteria, fungi, and viruses to thrive and multiply.

Destroy infected plants. Throw away or burn infected plants. Don’t keep infected plants over the winter in your garden, and don’t throw them on your compost pile. Disease-ridden plants, even when dead, will spread disease to other plants or even your soil.

Common Tomato Diseases

Here are some of the usual culprits that might infest your tomatoes. Remember, it’s important to remove infected plant material (leaves and roots) to prevent the spread of disease once it’s found its way onto your plant.

Anthracnose

Cause: Fungus

Symptoms:

• leaves turn yellow at the tips, eventually turning brown all around
• browned, dying leaves
• dark, sunken lesions on fruit and/or stems

How it spreads:

• spores spread by rain and splashing water
• wind

Treatment:

• remove all infected parts
• clear ground of leaf and twig litter
• apply liquid copper fungicide to reduce recurrence

Prevention:

• prune plant to provide good air circulation and access to sunlight
• provide proper water and fertilizer

Bacterial leaf spot

Cause: Bacteria

Symptoms:

• leaves have circular spots with irregular edges
• spots may turn yellow and water-soaked
• leaf drop

How it spreads:

• water
• wind
• garden tools
• thrives in warm, moist conditions

Treatment:

• remove and discard infected leaves
• if infection becomes serious, discard entire plant
• do not compost infected plant material

Prevention:

• mulch around plants to prevent water from splashing onto leaves
• avoid overhead watering; water at soil level
• make sure plants have good air circulation and lots of sun
• sterilize garden tools before each use
• spray plants weekly with neem oil or a commercial fungicide, such as Bonide Revitalize
• rotate crops annually

Blossom-end rot

Cause: Calcium deficiency

Symptoms:

• water-soaked area on end of fruit where the flower was
• lesion on side of fruit
• lesion enlarges and turns brown and leathery

How it spreads:

• caused by a calcium deficiency in the soil

Treatment:

• keep soil pH between 6.5 and 6.8
• lime soil to increase calcium content
• mulch to retain soil moisture

Prevention:

• test soil before planting
• water consistently
• avoid excessive amounts of nitrogen fertilizer

Cercospora leaf spot

Cause: Fungus overwinters in infected plant material and emerges in warm, humid weather, most commonly after a rainy spell. It does not affect the fleshy root of the plant. In the U.S., this infection is most prevalent in the southeastern states.

Symptoms:

• yellow and brown spots on the underside of leaves
• leaves may curl and turn upward

How it spreads:

• fungus overwinters in infected plant material
• wind, insects, and birds

Treatment:

• removed and destroy infected areas

Prevention:

• apply liquid copper fungicide
• if necessary, apply sulfur-based fungicide
• plant disease-resistant varieties
• remove plant debris
• rotate crops annually; see crop rotation guidelines above

Damping-off

Cause: Fungus

Symptoms:

• water-soaked, decomposing seeds
• infected roots are gray and water-soaked
• seedlings grow but then collapse and die
• older plants that get infected are severely stunted

How it spreads:

• spores thrive in moist soil and cool temperatures

Treatment:

• if infection is severe, apply liquid copper fungicide
• remove and discard infected parts

Prevention:

• minimize soil moisture
• plant in well-draining areas
• avoid overhead watering; water at soil level
• treat seeds with fungicides before planting
• rotate crops annually; see crop rotation guidelines above

Fusarium wilt

Cause: Fungus

Symptoms:

• leaves wilt and turn yellow

How it spreads:

• splashing water (rain, irrigation) disturbs spores
• warm temperatures favor growth

Treatment:

• destroy infected plants

Prevention:

• purchase disease-free plants
• plant in well-draining areas
• use homemade fungicides
• choose planting sites with good air movement

Gray leaf spot

Cause: Fungi present in the soil

Symptoms:

• small red-brown spots on leaves
• lesions expand and turn lighter in the middle
• mature lesions have white or gray centers and dark margins
• leaf drop

How it spreads:

• splashing water
• contact with other infected plants

Treatment:

• remove and discard infected plant matter

Prevention:

• buy disease-free seeds
• avoid overhead watering; water at soil level
• make sure plants have good air circulation and lots of sun
• rotate crops annually; see crop rotation guidelines above

Mosaic virus

Cause: Viruses

Symptoms:

• small, light-colored spots on the youngest leaves of the plant
• leaves turn pale yellow between the veins
• leaf death
• stunted roots

How it spreads:

• aphids

Treatment:

• disease is not treatable
• discard all infected plant material
• do not compost

Prevention:

• keep aphids away from plants; once aphids appear, plants are at risk of infection
• use floating row covers with hoops to accommodate plant growth
• use companion plants like asters, nasturtiums, and nettles to attract aphids away from tomato crops
• plant repellent plants like catnip, dill, and marigold
• interplant cilantro, cosmos, and geraniums to attract ladybugs, which love aphids
• spray plants with a mixture of 4 parts mineral oil to 1 part dish soap to smother any insects that land on the leaves
• do not save seeds from infected plants
• avoid planting in cool, wet weather
• avoid overhead watering; water at soil level
• make sure plants have good air circulation and lots of sun
• rotate crops annually; see crop rotation guidelines above

Southern blight

Cause: Fungi present in the soil

Symptoms:

• leaves wilt and turn brown
• fungus visible on plant stem and surrounding soil
• discolored stem

How it spreads:

• fungi living in the soil
• disease emerges in times of high temperatures, high humidity, and acidic soil
• most frequently found in southern U.S.

Treatment:

• remove and discard infected plant matter

Prevention:

• buy disease-free seeds
• avoid planting in cool, wet weather
• avoid overhead watering; water at soil level
• make sure plants have good air circulation and lots of sun
• rotate crops annually; see crop rotation guidelines above

Powdery mildew

Cause: Fungus overwinters on infected plant debris and emerges in warm, humid weather

Symptoms:

• white, powdery patches on leaves
• leaves may curl and turn upward
• new shoots appear stunted
• older infections look like a tan or reddish-brown felt covering; these contain spores
• heavy mildew infections can stunt a plant’s growth

How it spreads:

• fungus overwinters in infected plant debris
• spores do not need moisture to germinate; often called a “dry weather disease”
• wind, insects, and birds

Treatment:

• removed and destroy infected plant matter

Prevention:

• apply liquid copper fungicide
• if necessary, apply sulfur-based fungicide
• plant disease-resistant varieties
• remove plant debris
• rotate crops annually; see crop rotation guidelines above

This is not an exhaustive list of the ailments that may plague your tomato crop. Other potential bacterial, fungal, or viral infections include:

• Bacterial canker
• Verticillium wilt
• Magnesium deficiency
• Nitrogen deficiency
• Tomato spotted wilt virus
• Phytophthora blight

If you’re not sure what’s wrong with your tomato plants, take good close-up pictures and contact your local garden center or extension center for advice. Many diseases present with similar symptoms, but the treatment for them may vary. In general, you can reduce the likelihood of fungal infections with careful, consistent watering. It’s not a failsafe, but it’s good gardening practice.

Which diseases have you had to treat on your tomatoes? Please tell us how you prevent and handle diseases. If you spot other symptoms on your tomatoes that are not mentioned here, contact your local extension center or garden center for a consult—and please let us know what you discover.