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How To Identify and Treat the 7 Most Common Tomato Plant Diseases

Have you ever been so excited about your new tomato garden, only to go outside one morning and see spots on your leaves? You water and you tend and you do everything you know to do and the plants still don’t thrive.

Frustrating, right?!

A tomato plant infected by late blight, a devastating tomato plant disease.
Knowing about tomato plant diseases can keep this from being the outcome for your tomatoes.

Unfortunately, there are a number of different tomato diseases your plant could be suffering from, but have no fear! We’re here to help you identify, learn about, and treat or manage some of the most common tomato plant diseases.

Read on to learn more about how to identify and treat the 7 most common tomato diseases.

1. Early Blight

Early blight is caused by the fungus alernaria solani and is very common. The leaves, stems, and fruits of the plants can all be affected. Early blight may not cause the plant to die, but they will be much weaker and set fewer tomatoes than they would if they were healthy. It generally attacks older plants and stressed plants or plants in poor health are especially susceptible.

Signs of early blight on tomato plant leaves.
Signs of early blight tomato plant disease on a tomato leaf.

Causes

Early blight fungus can come from many different sources. It can already be in your soil, or it could be o the seeds or seedlings you purchase. If your plants were infected the previous year and left in the ground, the fungus can persists in the soil or debris for at least one year. Early blight can occur in any weather, but it favors damp conditions, like frequent rain or heavy dews.

Symptoms

If your tomato plant is being affected by early blight, you’ll see dark spots with concentric rings develop on older leaves first. Once that happens, the surrounding leaf may turn yellow and eventually die prematurely, exposing the fruits to sun scald.

You may also see dark lesions on the stem that start small and slightly sunken. As they grow, they’ll elongate and you’ll start to see the concentric markings like the spots on the leaves. If a spot forms near ground level, it can cause some girdling of the stem or even collar rot. Plants can survive, but they won’t thrive or produce a big harvest of fruit.

This tomato disease can get on the actual tomato, too. Spots will begin at the stem end, creating a dark, leathering, sunken area with concentric rings.

Signs of early blight on a tomato fruit.
The effect of early blight on a tomato fruit.

Treatment/Management

Early blight is common enough that you may not be able to avoid it completely, but here are a few idea that can help you keep it under control.

1. Air Circulation: Make sure there’s plenty of space for air circulation around plants. Prune away any big, bottom leaves. Good airflow will help keep the plants dry.

2. Garden Sanitation: Many tomato diseases can enter your garden through plant debris and in the soil from the previous season. It’s important to clean up and take away all plant residue at the end of the season to help prevent that transfer of fungus.

3. Fungicides: Fungicides containing the active ingredients Penthiopyrad or Boscalid will be most effective.

4. Rotate Crops: If you have an outbreak of Early Blight one season, find a different place to plant your tomatoes the following year. You can even plant them in containers for a season!

5. Remove Diseased Plants: Keep an eye on your tomato plants, especially if they’re stressed or during wet weather. If you see early blight signs on a single plant, quickly remove the entire plant to stop the fungus from spreading.

2. Late Blight

Unlike early blight, late blight is not survivable. This nasty tomato disease can wipe out an entire crop of tomatoes quickly if not identified and dealt with quickly. In fact, late blight was the cause of the potato famine in Ireland in the 1840s that killed over a million people.

Shriveled tomato plant leaves infected by late blight.
Tomato leaves showing signs of late blight tomato disease.

Causes

Late Blight is caused by a fungus, phytophthora infestans. It’s a fungus that has adapted for growth where water is present and cool temperatures persist. The moist conditions allow spores to spread among plants by splashing rain, overhead irrigation, and wind.

Symptoms

Early symptoms include irregular gray or olive-colored water-soaked lesions on the leaves and stems of your tomato plants. A mildew-like white mold may also be present on or near these lesions. While early blight causes some leaves to fall off, leaves affected by late blight usually stay attached even after they’ve turned brown and dry up. Infected fruits develop large, sunken, brown spots.

A tomato fruit showing signs on late blight infection.
How late blight tomato disease appears in the fruit.

Treatment/Management

While plants that get infected with late blight can rarely be saved, there are steps you can take to prevent and control the fungus.

1. Keep Things Dry: Keep the foliage as dry as possible. Use drip irrigation or water directly at the base of the plant rather than overhead watering.

2. Root Out Infection: Uproot and quickly dispose of any infected plants in your garden. You can bury them deep in the soil outside of your garden or put them in a plastic bag before putting into your garbage can.

3. Shop Smart: Seek out late-blight resistant varieties of tomatoes.

4. Fungicide: Use a fungicide that contains bacillus subtillis, a bacterium that will stay in your soil and control a variety of diseases, including late blight.

3. Southern Blight

While tomatoes do really well in warm temperature, when warm rains follow dry, hot weather, southern blight can rear its ugly head and destroy your tomato plants! Like late blight, it’s not a slow tomato disease. It can knock out your entire tomato bed seemingly overnight.

Causes

Southern blight is caused by a fungus called sclerotium rolfsii. It’s a fungus strain that can hide, living dormant, in soil for three to four years. You can unknowingly transfer it via garden tools and pots, unsterilized soil, or even on the treads of your sneakers, tracked in from the nursery you visited earlier in the day.

Symptoms

The most common symptom is dark, round spots appearing on the lower stem near the soil line. The brown/black lesion will grow rapidly and can completely cover the stem, preventing the plant from taking water and nutrients.

The fungus will easily infect tomatoes that are touching the infested soil. Spots will first appear as sunken and slightly yellow areas that will turn into water-soaked, star-shaped, soft spots. In 3 to 4 days, white mycelium may fill the lesion cavity.

Treatment/Management

Once a plant is infected with fungus, the only way to get rid of it is to uproot and dispose of it, but there are steps you can take to mitigate the risk of southern blight.

1. Plan Planting Well: When planning your garden, modify planting dates to avoid conditions in which the fungus thrives.

2. Stake Plants: Stake tomato plants in a way that prevents them from touching soil. You can also prune the lower leaves that may still touch the soil.

3. Mulch: Apply a thick layer of mulch on top of the soil that will act as a barrier between the possibly infected soil and your tomato plants.

4. Sanitize: Take care to sanitize garden tools and wash hands thoroughly after each use.

4. Blossom End Rot

Unlike the problems we’ve talked about so far, blossom end rot isn’t caused by a fungus or bacteria. It’s actually a physiological disorder, attributed to a calcium deficiency during fruit set. Thankfully, the whole plant won’t be affected, just individual fruits.

Person holding unripe tomato with blossom end rot lesion.
Blossom end rot tomato disease.

Causes

As mentioned above, blossom end rot comes from not enough calcium being available to the tomato plants while the fruit is setting. It could be caused by uneven watering, too much high-nitrogen fertilizer, soil pH that’s either too high or too low, or even cold soil. It’s most common when the season starts out wet and then quickly becomes dry when fruit is setting.

Symptoms

The damage from blossom end rot won’t appear until the fruits are about half their full size. At the bottom of the fruit, where the blossom would’ve been, a water-soaked area will appear, enlarge, and turn a leathery dark brown. Eventually, that area will begin rot, so the fruit will need to be picked and discarded.

Person holding red tomato with blossom end rot lesion.

Treatment/Management

This tomato disease is something you’ve got to proactively treat and manage.

1. Water Consistently: Don’t water too much or too little. If you forget to water, don’t overwater to try to make up for the missed watering. If it’s rainy, skip watering it until the soil starts to dry out. As a general rule, water thoroughly once or twice a week until the soil is moist as deep as 6 inches.

2. Be Patient in Planting: Because cold soil will prevent the plant from absorbing nutrients correctly, wait until the soil is warmed up to 70°F.

3. Watch the Calcium: If you’re using new soil you bought from the store, it’s likely going to have more than enough calcium in it as it is. If you are growing in older soil, calcium levels may be lower than needed. Test it (tests are readily available at your local home and garden store) and see what the levels are. If calcium is low, add in an organic source of calcium like bonemeal, lime, or even finely crushed up eggshells.

4. Be Gentle: Avoid digging or cultivating near the roots of your tomato plants. Root damage will affect their ability to effectively absorb nutrients and water.

5. Verticillium Wilt

Don’t let the name fool you. While sometimes presenting as wilted plants, other times, your tomato plants will simply have yellow, dry leaves with no other answer besides verticillium wilt. While this disease won’t kill your tomato plant completely, it will leave the leaves dead or wilting and is going to stunt the plant’s growth and fruit production.

Causes

Verticillium wilt is caused by a fungus that lives in soil. It created threads that get into and infect plants through their root hairs. Verticillium thrives in early spring because it loves cool and wet conditions. A lot of times, your plants will be infected in the spring but not show any symptoms until summer when they’re older and more established.

Symptoms

If your tomatoes are infected with Verticillium wilt, the lower leaves will begin to show yellow spots that will eventually transform into dead brown lesions. It starts at the bottom and works its way up the plant. The fungus stunts the plant’s growth and fruit output, as well as making the tomatoes suffer from sun-scalding due to the shriveled and dying foliage not offering protection from the sun.

Tomato plant with spotted, shriveled leaves possibly due to verticillium wilt.

Treatment/Management

Like the other fungal diseases, there’s not much you can do for your tomato plants once you see them infected with Verticillium Wilt, but there are steps you can take to manage this tomato disease and prevent it from spreading or happening again in the future.

1. Plant Wisely: There are varieties of tomatoes naturally resistant to Verticillium Wilt. They will have the letter “V” after the name to show you which ones to buy.

2. Keep It Clean: The fungus is easily spread from plant to plant, so if you’re working with a plant you know is infected, wash and disinfect your hands and tools before moving on to an unaffected plant.

3. Crop Rotation: If you keep planting susceptible tomato plants in the same soil year after year, the fungus will build up and infections will keep happening. Every other year, plant something like cover crops, corn, or grains (all not as vulnerable to the fungus) where you planted your tomato plants to help reduce the fungus in the soil.

6. Anthracnose

Also known as leaf, shoot, or twig blight, anthracnose affects a wide variety of plants, including tomatoes. That makes knowing how to identify and control it that much more important!

Tomato fruit showing effect of anthracnose tomato disease.
Anthracnose tomato disease.

Causes

Anthracnose is a disease caused by a fungus that usually attacks plats in the spring when the weather is wet and cool. It usually presents on leaves and twigs. The disease can be cyclic, stopping during dry and hot weather and starting again when things cool down, but it’s rarely fatal.

Symptoms

Anthracnose is regularly misidentified as other tomato diseases, but there are ways to be sure. You’ll start seeing dark lesions along the leaves and veins. In order to determine if what you’re seeing is indeed anthracnose, you’ll need to carefully look at the underside of the leaves affected. Look for small tan or brown dots, about the size of a pin head. That’s what differentiates it from other diseases and is going to be the giveaway.

Tomato on the vine showing early signs of anthracnose.
Early signs of anthracnose tomato disease.

Treatment/Management

Because Anthracnose is known to rely on water to spread, there are several steps you can take to prevent it initially or stop/slow the spread after your plants are infected.

1. Spread Them Out: Again, make sure you plants have plenty of room to breathe. It’s recommended to plant them 18 to 24 inches apart. This gives them space to dry out and to not lean over and touch each other, furthering the fungus spreading.

2. Keep Everything Dry: Make sure you’re not working with the plants immediately after watering them. Anthracnose can spread between plants in the water on your hands, tools, shoes, or anything else it may stick to. Plan to prune, tend, and harvest during a time of day you know everything will be completely dry.

3. Fungicides: Copper based fungicides have been proven to help battle anthracnose.

7. Gray Wall

When your plants are looking good but your tomato fruit is still looking weird and off when it should be fully ripe, chances are good that you’re dealing with Gray Wall. While there’s no known pathogen associated with gray wall, there are ways to prevent it.

Causes

There are several causes that all work together to cause your tomatoes to ripen poorly or unevenly. Extreme heat, high humidity, or fluctuation in temperatures can stress plants into producing fruit with gray wall. Overly wet, compacted soil or too much shade can also cause blotchy ripening. The makeup of your soil can also have effects on your fruit. Too much nitrogen or not enough boron or potassium can also lead to gray wall.

Symptoms

Tomatoes affected with gray wall ripen unevenly, usually splotchy with red and yellow areas. The mottling starts to appear on green fruit before they begin to ripen and then as the fruit matures, these areas sometimes can turn gray and sink in. When an affected tomato is cut up, you’ll see the walls of the fruit are yellow, brown, green, or gray. Basically, anything but red.

Person holding tomato fruit affected by gray wall or blotchy ripening tomato plant disease.
Graywall, or blotchy ripening, tomato disease.

Treatment/Management

1. Prune Wisely: When skies are overcast but temperatures are very hot, clip some of the leaves above ripening fruit to allow sufficient light to reach them. Be careful to not over-prune, which could lead to sun-scald.

2. Remove Bad Fruit: This isn’t a tomato disease that will spread from fruit to fruit. Simply remove the bad fruit and do your best to help the other fruit get what they need to prevent it from happening again.

3. Watch the Soil: Test your soil to see what nutrients your tomato plants may be missing. Be careful to not overly compact the soil so that they is plenty of room for good drainage.

You Can Win the War Against Tomato Plant Diseases!

Closeup of healthy, thriving tomato plants with ripe, unblemished fruit.
Healthy, thriving tomatoes — the reward for knowing how to fight tomato plant diseases.

Now that you know so much about the common tomato plant diseases, you’ve got what you need to fight back whatever is in your garden and enjoy the fruits of your labor!

Let us know in the comments— what are you dealing with? How has this information helped you combat tomato diseases infecting your plants? Anything else we can help with? We love hearing from you! Click here for our other tomato blog posts.