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?!

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 a very common fungal tomato disease that affects almost every single part of the plant. While it won’t normally kill the plant, it will weaken it, resulting in a much lower yield of tomatoes. Older or stressed (too much heat, too little water) plants are highly susceptible.

Causes

The fungus that causes early blight can be introduced to your garden in a couple of different ways. It could be there because the seeds or seedlings you bought were already infected. Or it might’ve already been in your soil.

If any of your plants were infected previously and were left in the soil, the fungus can stay in the soil for up to a year. So even if you pulled them up at the end of the season and started fresh in the spring, the fresh baby plants could get infected from the fungus left behind from last season.

Early blight also loves wet conditions. If you’re in an area with a lot of rain or really heavy dews in the morning, you may be fighting this fungus more than in other areas of the country.

Symptoms

The first sign of early blight you’re going to see is dark spots with rings like a bullseye that will develop on older leaves first. The leaves may then turn yellow and fall off, which is going to leave any fruits already growing exposed to direct sun.

After the rings on the leaves, you might also see dark spots on the stem that start small and look like they’re eating away at the stem. As the spots get bigger, you’ll start to see a bullseye forming around the center of them, too. If a spot shows up near the ground, it may leave your plant with collar rot, meaning it’s not going to get enough nutrients up the stem to the leaves and fruit.

This tomato disease can get on the actual tomato, too. Dark spots will appear near the stem and will eventually turn into a dark, sunken bullseye.

Treatment/Management

Early blight is common enough that you may not be able to avoid it completely, but here are a few ideas 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. This will help keep everything from staying damp, which is where early blight thrives.

2. Garden Sanitation: Since many diseases can stick around in soil from the previous season, make sure to quickly and completely remove all plants and debris from your garden at the end of the season.

3. Fungicides: Fungicides containing the active ingredients Penthiopyrad or Boscalid will work the best to fight early blight fungus.

4. Rotate Crops: If Early Blight attacks your plants one season, move your tomato plants to another area of your garden or into containers the next year to give the soil time to rid itself of the fungus.

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.

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

The earliest symptoms of late blight are going to be irregularly shaped gray and yellow spots on the leaves and on the stem of your plant. A fuzzy white mold might also appear around those spots. One thing that differentiates early and late blight is that in late blight, leaves that have spots don’t fall off once they’ve been affected. Tomatoes on an infected plant will eventually show big, soft, brown spots.

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 plant as dry as possible. Use something like drip irrigation near the base of the plant or water with a hose directly at the base instead of from above the whole plant.

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 into your garbage can.

3. Shop Smart: Look for 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 several different diseases for an extended period of time.

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.

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.

Treatment/Management

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

1. Water Consistently: Don’t overwater or underwater. If you forget, don’t overwater to try to make up for the missed watering. If it’s rainy, skip watering 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 soil you bought from the store, it will probably already have more than enough calcium in it. If you’re planting your tomatoes in soil you’ve used before, the soil may need a little help getting calcium levels where they need to be. Test it (tests are readily available at your local home and garden store) and see what the levels are. If the levels are lower than they should be for your variety of tomatoes, add some organic matter like finely crushed up eggshells to add calcium.

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.

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!

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.

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.

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!

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!

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