19 Tomato Diseases: How to Identify, Treat, and Prevent Them

Tomato diseases can disrupt any tomato garden. There are many different kinds of disease that can strike tomatoes at different points in the growing season. In this article, gardening expert and former organic farmer Logan Hailey examines the most common diseases that will likely strike your tomatoes, as well as how to identify, treat, and prevent them from striking your tomato plants.

tomato diseases


You’ve seeded and carefully tended your baby tomato plants, but the leaves have suddenly started to look yellow or fruits are deformed. It looks like some sort of disease has overtaken those previously eager growing vines. You might be wondering, “What the heck is wrong with my tomatoes?”

Whether you’re a beginner or advanced gardener, tomato problems can be challenging to identify and overcome. It can be a little anxiety-inducing to suddenly see all your hard work falling victim to some unknown pathogen.

If you’re craving garden grown tomatoes in the peak of summer– don’t worry! All is not lost! Use this simple guide to identify, prevent, and treat the most common tomato diseases so you can keep your tomato plants thriving all season.

Early Blight

Vegetable Leaf With Brown and Yellow Spots
Symptoms of this disease are the appearance of brown spots with yellow rings in the form of a target.

Caused by the fungi Alternaria tomatophila and Alternaria solani, early blight is among the most common diseases afflicting tomatoes and their cousins, potatoes. It attacks all above-ground plant parts and can rapidly defoliate the plant, leaving flimsy fruit exposed to sun scald and reduced photosynthesis for the plant as a whole.

Because early blight is a fungal disease that begins in the soil, it is important to change out the infected soil before planting any new plants if you suspect early blight. Thankfully it is treatable if caught early, so learn the first signs to keep your plants healthy.

How to Identify

The first signs of early blight are tiny dark brown spots on the lower foliage of a plant. As the spots grow, they typically get a ring of yellow around the spot, giving a target-like appearance. The infection can spread quickly and begin causing leaves to turn yellow and brown, then fall off. You may also notice dried, dead leaves clinging to the stem.

How to Prevent

While resistant tomato varieties are available, the key to preventing early blight is to improve airflow, reduce splashing or moisture on the leaves, and ensure that you practice proper crop sanitation. This means spacing tomatoes farther apart (often 24-36” depending on variety and your trellis) and regularly pruning off lower leaves.

Avoid overhead irrigation, instead opting for drip irrigation or soaker hoses that deliver water straight to the root zone. Lastly, thoroughly remove and dispose of tomato debris at the end of the season. Leftover tomato debris from the previous crop is the most common source of disease. It can also spread by infected seeds or transplants.

How to Treat

If early blight has already taken hold of your tomatoes, you have a few options. First, carefully remove infected parts and dispose of them. Avoid doing this in windy or wet conditions because spores can easily spread. Be sure to wash your hands and sanitize your pruners after doing so.

Next, you can apply a diluted neem solution to help treat and prevent further spread. An organic copper fungicide or baking soda spray (1 tbsp. baking soda, 1 tsp. vegetable oil, and 1 tsp. mild soap in a gallon of water) can also help stop the disease).

Late Blight

Stems of Vegetable Plant Turning Black
To prevent the spread of late blight, immediately remove lightly infected plants from the area.

Unlike early blight, late blight is not caused by a fungus. A water mold called Phytopthora infestans is the hidden culprit. It is most well-known for causing the Irish Potato Famine.

Though a nationwide Tomato Famine is unlikely, late blight can still casue severe damage to a garden. This is why is it important to use sterilized garden tools and disease-resistant varieties. It can spread quite quickly, so pay close attention to your plants to find early signs.

How to Identify

First, the leaves looked like they’re soaked in water. Then, spots begin to enlarge into purple-colored oily blotches. You may notice outer rings of gray-white fuzzy on the underside of the leaves (this is the mycelia). Entire leaves and petioles will begin to die off. Fruits can also get infected by turning brown around the “shoulders” of the tomatoes.

How to Prevent

At high humidity and moderate temperatures (60-75°F), late blight can take hold in as little as 10 hours. You have to ruthlessly remove any slightly infected plants and get them off the property. Be sure that all crop debris from previous nightshade-family crops is completely removed from the garden at the end of every season. Choose blight-resistant varieties in the future.

How to Treat

Late blight is a tough one to beat because it spreads so rapidly. There is no real cure, but you can stop spread with preventative fungicides like copper, sulfur, or the safest option: neem oil.

Blossom End Rot

Unripe Fruit With Rotting Hole
To prevent this disease, regular watering and maintaining the correct level of calcium are necessary.

Though it’s not technically a disease, blossom end rot looks a lot like a pathogen. This physiological disorder is actually caused by a calcium deficiency in the soil.

Once it takes hold of the fruit, they have to be removed and discarded. This can be a bummer for gardeners who have worked hard to keep their tomatoes alive all summer! Thankfully, this untreatable problem in tomatoes can easily be prevented with proper soil nutrients.

How to Identify

The bottom ends of fruits (where the flower once was) look black, greyish, or sunken-in as if they are rotten.

How to Prevent

Consistent watering and proper calcium levels are the most important factors for preventing this problem. Use a soil test and, if necessary, amend with lime, bone meal, or eggshells. Ensure that plants are not heat or water stressed.

How to Treat

Once a fruit has begun to rot at the end, it is irreversible. Remove the affected tomatoes and try to fix the root cause to save future yields.

Botrytis (Gray Mold)

Red Fruits With Gray Mold Growing on Them
Botrytis appears on fruit when the environment has high humidity.

This gray mold is the bane of any gardener’s existence! In high humidity, botrytis fungus attacks a wide range of crops, from squash to grapes to tomatoes. It is usually the culprit for postharvest rotting of tomatoes in the grocery store or on the kitchen counter.

Though it is impossible to control humidity in the air when growing tomatoes, you can control how you space the plants when planting them into the ground. You can prune them to ensure proper airflow as well. It is also a good idea to never water tomatoes from overhead.

How to Identify

Gray mold typically begins by covering tomato flowers and young fruit. It looks like circular white spots that later turn yellow.

How to Prevent

Always avoid overhead irrigation with tomatoes. If you live in a moist climate, create more air circulation by increasing the spacing and pruning of your plants.

How to Treat

In the case of severe gray mold infections, remove all infected leaves or fruit. Sanitize your hands and pruners. Apply a neem oil, a horsetail (Equisetem) spray, or a diluted fungicide to kill any spores and prevent more infection.

Powdery Mildew

Vegetable Leaf With Powdery White Substance
To prevent the spread of the disease, clean the garden frequently by removing plant debris and maintaining airflow.

While zucchini and cucumbers are the most notorious victims of powdery mildew, this fungus readily attacks tomato foliage as well. Hot, dry weather in mid-summer – especially when coupled with moist cool nights – tends to cause the worst mildew infections.

Powdery mildew is another fungal disease on this list. Proper watering from underneath, as well as attentive garden maintenance, are good ways to prevent this disease. However, it can creep up in just about any vegetable garden.

How to Identify

Powdery mildew looks like a gray or white flour has been sprinkled on your tomato leaves. Circles of dead tissue may be surrounded by a yellow halo.

How to Prevent

Resistant varieties (labeled “PM” in seed catalogues) tend to be the easiest means of prevention. You should also focus on cultural controls like cleaning up crop debris, removing pruning, maintaining airflow, and avoiding overhead irrigation.

How to Treat

The biofungicide Bacillus pumilus is one of the safest and most effective sprays for powdery mildew. However, most gardeners remove infected foliage, prune more leaves, and then apply a diluted neem solution before resorting to fungicide applications.

Fusarium Wilt

Gloved Hand of a Gardener Holding Stem of a Diseased Vegetable Plant
The most characteristic symptom of this disease is the ‘yellow flag effect’.

This devastating wilt is caused by a fungus called Fusarium oxysporum f. sp. lycopersici. This crazy long name is almost a metaphor for how long these spores can live in the soil– you don’t want to mess around with this one!

There is no cure for fusarium wilt. The key to avoiding its awful fate is buying disease-resistant tomato seeds. Thankfully, there are a number of tomato varieties to choose from that were bred to be disease-resistant.

How to Identify

Infected yellowing leaves rapidly wilt, no matter how much water they receive. The most notable characteristic of this particular disease is the “yellow flag effect” where only one side of the plant wilts, while the other remains green and normal.

How to Prevent

The best prevention is growing resistant varieties (labeled “F”, “FF”, or “FW” in seed catalogues). Some of our favorites are ‘Big Beef Plus’, ‘Sun Gold’, Better Boy’, ‘Beefmaster’, or ‘Early Girl’.

You also want to control root knot nematodes in your tomato patch, as they can damage the roots and cause plants to be more susceptible. Certain companion plants for tomatoes (such as white mustards and marigolds) can help suppress nematodes.

How to Treat

Unfortunately, fusarium wilt is incurable. It can become permanent and live in the soil for decades. You can suppress the spread by removing infected plants and some volume of the infected garden soil. Always clean and sanitize garden tools and boots after dealing with this pathogen.

Fusarium Root Rot

Dry Yellow Leaves on the Stem of a Vegetable Plant
Fusarium root rot spreads most in waterlogged soils.

Like fusarium wilt, this root rot is detrimental. The spores are long-lived and affect a wide variety of crops as well as weeds. They especially love waterlogged soils, so it is very important to use well-draining soil when planting and make sure you are watering your tomatoes at the proper rate.

This disease begins at the plant’s roots and works its way up the stem and into the leaves and fruit. You may notice yellowing leaves as the first sign of infection. Once the plant starts showing symptoms, it is most likely going to need to be dug up and disposed of.

How to Identify

Fusarium root rot attacks the roots of young or weak plants, causing wilting and stunting. Above-ground, the oldest leaves begin to show symptoms first. They start to turn yellow along the edges and rapidly die.

How to Prevent

Maintain properly aerated, well-drained soil by adding plenty of organic matter, regularly broadforking, and avoiding tillage. Don’t overwater tomatoes. Choose resistant varieties (labeled “FOR” in catalogues), including ‘Supersweet 100’, ‘Cherry Bomb’, ‘Sakura’, or ‘New Girl’.

How to Treat

There are no known controls for this disease. Prevention and sterilization practices are key.

Black Mold

Small Red Vegetable Decaying From Disease
Black mold likes wet fruit, so avoid overhead irrigation.

When you get a bunch of late-season rains, this nasty disease can suddenly attack ripe tomatoes hanging on the vine. It is caused by the fungus Alternari alternata, which loves wet fruit.

Though we cannot control the rain, we can control the method we use to water our tomatoes. Always water vegetables, including tomatoes, from underneath! This will help prevent the spread of fungal diseases or mold.

How to Identify

In warm and humid weather, you will notice black velvety lesions on tomato fruits. These will grow into circular, sunken lesions that decay ripe fruits.

How to Prevent

The easiest means of prevention is to simply harvest your tomato fruits just before they fully ripen (especially if rain is on the way). Always avoid overhead irrigation, particularly during the late summer. Try to keep fruit as dry as possible.

You should also try to protect fruits from sun scald by keeping them shaded beneath leaves. Remove dead or infected parts out of the garden.

How to Treat

In rainy years, both organic sprays (like neem) and conventional fungicides (like calcium chloride) may be necessary to kill Black Mold. However, you will have to thoroughly wash fruits before consuming. It is much easier to harvest them a little earlier and ripen near bananas in your kitchen.

Tobacco Mosaic Virus

Vegetable Plant Leaves With Viral Infection
A symptom of the Tobacco Mosaic Virus is a mosaic pattern on the leaves.

Tobacco Mosaic Virus (TMV) attacks tobacco and all of its nightshade cousins, including tomatoes. Unfortunately, research has found that this persistent virus can survive up to 100 years in dead, dry plant debris.

This is why it is crucial to remove any dead or dying plants that have this disease. Keeping them around can cause the virus to stay in the soil. Do not compost it either! It will survive in the compost pile and infect other plants in the garden.

How to Identify

A mosaic-like pattern on tomato leaves is the characteristic symptom. The leaves may become deformed, curled, and fern-like.

How to Prevent

Never smoke or use tobacco products near your tomato plants. Choose resistant cultivars (labeled “TMV”) and always source from a reputable disease-tested seed company.

How to Treat

There is no way to treat TMV.

Tomato Spotted Wilt Virus

Red Fruits Suffering From a Viral Infection in a Garden
Tomato Spotted Wilt Virus is spread by pests such as thrips.

Another viral disease, Tomato Spotted Wilt Virus (TSWV) can infect a massive range of vegetables and ornamentals. It used to only be a problem in tropical regions like Hawaii, but it has since spread globally. TSWV is unique because it is spread by specific tomato pests called thrips.

Thrips are very small insects that have fringed wings. They feast on fruits by puncturing the outer layer and sucking the insides out, like little fruit vampires. If you ever see thrips in your garden, blast them with a hose or use an insect repellant.

How to Identify

Young leaves turn bronze and then accumulate dead spots on the surface. Ripened tomatoes can also show symptoms of blotchy yellow spots with rings on the outside (it’s safe to cut them off and still eat the fruit).

How to Prevent

Controlling thrips is actually the secret to keeping this virus at bay. Try interplanting with aromatic tomato companions that repel pests and attract predatory insects.

You can also opt for resistant cultivars like ‘Summerpick’, ‘Big Beef Plus’, ‘Plum Regal’, or ‘Red Defender’.

How to Treat

There is no known control. Practice crop rotation to try to avoid re-contamination.

Alfalfa Mosaic Virus

Gardener Holding an Infected Unripe Fruit
This virus is spread by aphids, so prevention methods should be aimed at getting rid of these pests.

This fatal disease mainly affects gardeners who grow tomatoes near alfalfa fields. Almost all commercial alfalfa fields in the U.S. have the AMV virus. It is easily spread between species via aphid feeding. You may need to investigate neighboring gardens or farms to see if this is the culprit.

Aphids are tiny bugs that survive by sucking sap from plants. They can be black, green, red, gray, or orange. Releasing natural predators, such as ladybugs, can be one way to deter aphids from eating your plants and spreading diseases.

How to Identify

Yellowing leaves with mottled, mosaic-like patterns are the primary symptom. There may also be concentric rings of dead spots on fruit.

How to Prevent

Avoid planting tomatoes near alfalfa. Plant beneficial companions to keep aphid populations in check. One experimental prevention strategy is to use reflective silver mulch below the tomato planting to help repel aphids and stop spread. This can have mixed results, but it’s worth a shot if you’re in alfalfa-country.

How to Treat

There are no known chemical controls. Getting rid of aphids may help lessen the spread.

Bacterial Leaf Spot

Vegetable Leaves With Bacterial Infection
As the disease spreads, the leaves may begin to die back.

This disease can range from moderate infections to killing whole plants. It frequents warm, wet climates in the midwest and the eastern U.S. Caused by Xanthomonas campestris pv. vesicatoria, this disease is known by small spots that spread on the foliage.

Bacterial leaf spot affects edible plants as well as ornamental. It is one of the most destructive and prevalent diseases for vegetable gardens. Prevention is of utmost importance becasue once your plants are heavily infected, there is no saving them. However, it can be treated if caught early enough.

How to Identify

Bacterial spots can occur on all above-ground plant spots. First, leaves may have water-soaked circular lesions. The spots start out green or yellow, then darken to reddish-brown. As it progresses, severe leaf yellowing and death occurs. On fruit, spots may look like raised blisters with a yellow halo.

How to Prevent

Preventing this bacterial disease is all about sourcing pathogen-free seeds and transplants. Keep tomato leaves dry and avoid handling them when wet. Sanitize your tools and hands after touching potentially infected areas. Practice crop rotation and always burn or dispose of tomato debris.

How to Treat

Plants with bacterial leaf spot can’t be cured, but you can try to stop the spread with copper or neem applications. Avoid eating infected fruit.

Bacterial Wilt

Vegetable Plant With Wilting Leaves
The main symptoms of bacterial wilt disease are rapid wilting of the leaves and yellowing.

Unlike bacterial spot, bacterial wilt is a soil-borne disease. It is most common in subtropical southern regions of the U.S. It can spread to tomatoes, potatoes, peppers, tobacco, and a range of Solanaceous ornamentals.

Becasue this disease can spread so rapidly, it is best to remove all infected plants and destroy them. It is also recommended to not plant anything else in that soil until it has been remediated. It is a tough disease to control so early prevention is the only way to keep it out of the garden.

How to Identify

As the name implies, rapid sudden wilting and yellowing of leaves are the main symptoms of bacterial wilt in tomatoes. To decipher it from other wilt-causing pathogens, look in the inside stems of infected plants. Take a clean, cut section of the diseased stem and place it in clear water. It will appear brown and decaying, with a milky slime of bacterial cells streaming into the water.

How to Prevent

Removing and destroying infected plants is an important means of prevention. Maintain well-drained soil and take care to control root knot nematodes (which can exacerbate thew bacterial infection). Avoid damaging or wounding tomato plants during planting. You should also always remove all plant debris from the garden.

How to Treat

Once soils are infected with bacterial wilt, it isn’t technically curable. Your best bet is planting tomatoes in other parts of the garden. You can also try remediating the soil with diverse soil inoculants of beneficial microorganisms that can outcompete the pathogens.


Vegetable With Fungal Disease on a Vine
To prevent this anthracnose fungus, avoid sprinklers and provide well-drained soil.

This is a very common disease that can infect any part of the plant but mostly appears in ripe or overripe fruit that are still on the vine. The fungus Collectotrichum coccodes prefers hot weather and plants damaged by flea beetles or early blight.

Anthracnose can also affect tomatoes in storage or when they are ripening postharvest. There are copper based fungicides that can be used to prevent this disease but removing the infected fruits also works. As long as you cut out the infected area, the infected fruit is safe to eat.

How to Identify

Small, circular, and/or sunken lesions on fruit begin about one-half inch in diameter and later turn brown. You can often see a small black speck in the center of the lesion, which is why this disease is also called “tomato black dot” rot. Similar symptoms can appear on lower leaves and roots, leading to widespread rotting.

How to Prevent

This fungus primarily takes hold on wet leaves and fruit, so avoid overhead irrigation at all costs. Rotate nightshade family crops around the garden and ensure well-drained soil.

How to Treat

Standard organic or conventional fungicides can control anthracnose, however, many gardener’s opt to remove infected fruit and wait for the next round of tomatoes.

Septoria Leaf Spot

Fungal Disease on the Leaves of a Nightshade Plant
This fungus overwinters in tomato debris, so it is necessary to sanitize before sowing.

Wet, humid weather is a recipe for disaster in tomatoes. The fungus Septoria lycopersici loves to colonize tomato leaves in mid-summer rain storms after the first fruit set. It overwinters in tomato debris, so sanitation is the first key step to prevention.

Disinfecting all garden equipment, especially pruning shears, is the first step to preventing fungal diseases such as septoria leaf spot. Proper spacing of the plants when plating in the garden also improves airflow, meaning moisture has less of a chance of being trapped.

How to Identify

Septoria leaf spots are circular and less than ¼ inch in diameter. They are speckled around the leaf and begin on the oldest growth first. The disease may start to cause yellowing, browning, and death of leaves. The spots won’t usually show up on fruit.

How to Prevent

Improving air circulation is key for this disease. Avoid overhead irrigation, control weeds, and mulch around the base of the plants to prevent rainfall splash.

How to Treat

Remove and dispose of all diseased leaves. In a severe infection, you can apply fungicides such as copper or neem to stop the spread.

Southern Blight

Tomato Plant Suffering From Blight Disease
One of the important preventive measures is the removal of fallen leaves and plant debris.

Dry, hot weather that alternates with warm summer rains creates the perfect conditions for this fungus. It is typically minor, but it can wipe out whole plantings of tomatoes in just a few hours in ideal conditions.

If the fruit begins to look off, usually squishy and juicy, then it is possible it may be infected with southern blight. There will also be lesions near the soil line on the stem. You may also notice white fungus growing around the base of the plant. Once it takes hold of there plant, there is little you can do.

How to Identify

Rapid yellowing and wilting appear first. Then comes a white fungal appearance at the soil line near the base of the plant, as well as lesions that appear wet or soaked on the stems. Fruit also can take on a rotten, watery appearance.

How to Prevent

The number one most important preventative method is removing dead leaves and plant debris. This fungus lives in the top few inches of soil, persisting on decomposing tomato matter. You should also purchase only disease-free plants, remove infected plant parts, avoid overhead irrigation, and sanitize garden tools. Widen spacing if it is a recurring problem.

How to Treat

Solarization of soil with clear plastic has proven successful for many growers. You can also use organic or conventional fungicides.

White Mold (Timber Rot)

Vining Fruit With White Fuzz on the Plant
Stems affected by this disease look discolored and withered.

This disease is fortunately quite rare, however, it can be detrimental when it appears. This fungus produces massive amounts of spores that are spread by wind. It will typically appear on the plant when it flowers.

Stems will the the first to look infected. This is becasue the fungus lives in the soil and moves up in the stems of the plant. It will eventually be seen in the fruit and leaves of the plant if untreated.

How to Identify

You will notice stems that start to look bleached and dried out, like a dead tree. The black scleorita (hard fungal structures) hang out in the soil near the base of the plant.

How to Prevent

Continuous wetness and high humidity seem cause the highest infection rates. Keep the soil near the base of the plant as dry as possible using subsurface drip irrigation and a fluffy, lightweight mulch like straw. Avoid overhead irrigation and maintain proper aeration between plants.

How to Treat

In severe infections, copper and sulfur fungicides can be used.

Phytophthora Root Rot (Buckeye)

Red Vegetable Infected With Rotting Disease
To avoid the appearance of Buckeye, systematic and proper watering is necessary.

The worst damage from this root rot happens in compacted, poorly drained, and overwatered soils. Like many soil-borne fungal diseases, it is vital to properly manage moisture and irrigation to keep this pathogen at bay.

Fruits that are incontact with infected soil are typically the first to display symptoms. This is why it is important to plant tomatoes in soil that is well-draining, do not allow the soil to become waterlogged, and never water your plants from overhead.

How to Identify

Tomato roots first get distinctive brown lesions when infected with this fungus. They turn brown or yellowish and may begin to girdle or rot away. The above ground symptoms include wilting or death of plants in hot weather. If fruits come in contact with the pathogen, they get brown and tan concentric rings on the surface (hence the name “buckeye”).

How to Prevent

Double-dig tomato beds with a broadfork and thoroughly amend with organic matter to improve drainage and soil structure. Avoid compacted soils and flooding at all costs. Try to maintain consistent soil moisture rather than fluctuating between dry and wet periods. Gardeners have seen some success mitigating the infection when the rotate with cover crops.

How to Treat

In soils with very poor drainage, you may opt for fungicide use.

Bacterial Canker

Gardener Holding Red Fruit With Small Yellow-Brown Spots
Buy seeds from a reputable company, as infected seeds are the primary culprit in disease development.

In ultra-wet weather or greenhouse conditions, the bacteria Clavibacter michagensis can wreak havoc on tomatoes, causing a total crop loss. Infected seeds are the primary culprit, so it is vital that you source your tomatoes from a reputable company.

These companies can be found online or at your local plant nursery. Some big box garden centers will also have seeds you can purchase. If you are uncertain of the quality of the seeds, there is one way to treat the seeds to rid of any harmful pathogens.

How to Identify

Wilted and stunted growth are the initial signs of infection. Leaves may begin to turn yellow and brown, then get the characteristic curled appearance. Sometimes there are “bird’s eye spots” on fruit that look like raised circles with a white margin.

How to Prevent

Researchers at the University of California Davis have found that soaking tomato seeds in hot water (above 130°F) for 25 minutes before planting can eliminate the pathogen. You should also thoroughly sanitize greenhouse structures and garden tools. Rotate nightshades around the garden every year.

How to Treat

Copper can be used to help control the infection, but it won’t completely eliminate bacterial canker. Always remove and destroy affected crop debris.

Final Thoughts

Tomatoes are among the easiest, most vigorous garden crops. However, they still have a range of pathogens as eager to eat them as you are! Keeping these diseases out of your garden can be relatively easy with a few key preventative steps.

  • Maintain airflow: Proper spacing and pruning of tomato plants can help prevent disease.
  • Dispose of diseased plants: Throw away diseased plant parts, do not compost.
  • Ensure well-drained soil: Amend with organic matter and keep soil well drained.
  • Avoid overhead irrigation: Watering from the base of the plant will prevent most diseases.

With the proper care and disease prevention, tomatoes will eagerly yield all summer long. If you’re in an extra humid or disease-prone area, choose resistant hybrid varieties for the best results.