What Causes Brown Spots On Tomatoes

If you’re finding brown spots on tomatoes in your garden, you’re not alone. This is a common garden problem with several possible causes, ranging from simple fixes to more serious diseases. Let’s look at the main reasons so you can identify and adress the issue on your plants.

Those unsightly brown, black, or yellow spots can appear for many reasons. The key is to look closely at the pattern, location, and timing. Is the spot on the leaf, the stem, or the fruit itself? Is it a small dot or a large blotch? Answering these questions is the first step to a healthy garden.

1. Blossom End Rot: A Calcium Problem

This is one of the most frequent causes of brown spots on tomato fruit. You’ll see a dark, leathery spot on the bottom (blossom end) of the tomato. It often starts when the fruit is green.

It’s not caused by a fungus or bacteria, but by a lack of calcium in the fruit.
This calcium deficiency is usually due to irregular watering. Dry soil stops the plant from taking up available calcium.
Fast growth or root damage can also contribute.

How to fix it:

Water deeply and consistently. Aim for 1-2 inches per week, more in extreme heat.
Mulch around plants to help soil retain moisture.
Avoid over-fertilizing with high-nitrogen fertilizers, which promote fast growth.
Check soil pH; it should be between 6.5 and 6.8 for proper calcium uptake.

2. Early Blight: The Classic Fungal Foe

Early blight is a widespread fungal disease. It shows up as circular, target-like brown spots with yellow halos on lower leaves first. Stems and fruit can also develop dark, sunken spots.

It thrives in warm, humid weather and spreads via water splash.
Spores live in soil and on old plant debris.

How to manage it:

Water at the base of plants, not overhead, to keep leaves dry.
Space plants properly for good air circulation.
Remove and destroy badly infected leaves.
Use a fungicide containing chlorothalonil or copper, following label instructions carefully.
Rotate crops yearly; don’t plant tomatoes in the same spot for 3 years.

3. Late Blight: A Serious Disease

Late blight is more severe and can destroy plants quickly. Look for irregular greasy-looking gray-green spots on leaves that turn brown. White fuzzy mold may appear underneath in humid conditions. Fruit develop large, firm brown spots.

It spreads rapidly in cool, wet weather.
This is the same disease that caused the Irish Potato Famine.

How to manage it:

Remove and bag infected plants immediately. Do not compost them.
Prevention is critical. Choose resistant varieties when possible.
Apply preventative fungicides before weather turns favorable for the disease.

4. Bacterial Spot and Speck

These are less common but cause distinct symptoms. Bacterial spot creates small, water-soaked spots on leaves and fruit that turn brown and scabby. Bacterial speck causes tiny, dark brown spots on fruit, often with a white halo.

They spread in warm, rainy weather.
The bacteria can come from infected seeds or transplants.

How to manage it:

Buy certified disease-free seeds and transplants.
Avoid working in the garden when plants are wet.
Copper-based sprays can offer some protection but are not a cure.
Remove and destroy infected plants at season’s end.

5. Septoria Leaf Spot

This fungus causes many small, circular brown spots with tan centers and dark borders on lower leaves. The centers may have tiny black specks (fungal spores). Leaves turn yellow and fall off.

It weakens the plant by reducing its leaf area.
It spreads easily through water splash.

How to manage it:

Follow the same cultural practices as for Early Blight: water at base, space plants, remove infected leaves.
Mulch heavily to prevent soil from splashing onto leaves.
Apply appropriate fungicides early in the season if you’ve had problems before.

6. Sunscald: An Environmental Issue

This isn’t a disease. Sunscald appears as pale white or yellowish patches on green or ripening fruit that later turn dry, papery, and brown. It happens when fruit that was shaded is suddenly exposed to intense sun, often after leaf loss from pruning or disease.

It’s most common in hot, sunny climates.
The affected area can be invaded by secondary rot.

How to prevent it:

Avoid excessive pruning that removes to much leaf cover.
Manage diseases that cause leaf drop.
Use shade cloth during peak summer heat if needed.

7. Nutrient Deficiencies

Sometimes, brown or yellow spots on leaves signal a lack of key nutrients. Potassium deficiency, for example, causes yellowing and browning along leaf edges and between veins.

A soil test is the best way to confirm a deficiency.
Over-fertilizing can cause problems too, like salt burn on roots.

How to fix it:

Get a soil test every few years to guide your fertilization.
Use a balanced, slow-release fertilizer or one formulated for tomatoes.
Amend soil with compost annually to improve overall nutrient availability.

8. Pest Damage

Certain pests can cause spotting that looks like disease. Stink bugs and leafhoppers pierce fruit and leaves, leaving small, cloudy spots or specks that may turn brown.

Check the undersides of leaves for insects.
Pest damage is often more scattered than disease patterns.

How to manage it:

Hand-pick larger insects like stink bugs.
Use insecticidal soaps or neem oil for smaller pests.
Encourage beneficial insects like ladybugs by planting flowers nearby.

Prevention is Your Best Strategy

A healthy plant is your first line of defense. Start with these foundational practices to prevent many causes of brown spots on tomatoes.

Choose Resistant Varieties: Look for letters like “EB” (Early Blight), “LB” (Late Blight), or “VFN” (Verticillium, Fusarium, Nematodes) on plant tags.
Water Wisely: Deep, infrequent watering is better than daily sprinkles. Soaker hoses or drip irrigation are ideal.
Mulch Thoroughly: A 2-3 inch layer of straw or wood chips prevents soil splash and keeps moisture even.
Clean Up: At the end of the season, remove all tomato plant debris from the garden to reduce overwintering spores.
Rotate Crops: Don’t plant tomatoes, peppers, potatoes, or eggplants in the same bed for at least two years.

When to Use Fungicides and Other Sprays

Chemical controls should be a last resort. If you need them, here’s how to use them effectively.

Identify the problem correctly first. Using the wrong product wastes time and money.
Start applications early, often before you even see disease, if it’s a recurring issue.
Always follow the label directions for mixing, application, and safety gear.
Rotate between different fungicide classes (if applicable) to prevent resistance.
Spray on calm days to ensure the product goes on your plants, not your neighbors yard.

FAQ: Brown Spots on Tomatoes

Are tomatoes with brown spots safe to eat?
It depends on the cause. Fruit with blossom end rot, sunscald, or minor pest damage is fine to eat if you cut away the affected area. Do not eat fruit rotted by fungal or bacterial diseases.

What is the most common cause of brown spots?
For the fruit itself, blossom end rot is extremely common, especially early in the season. For leaves, Early Blight and Septoria Leaf Spot are the usual suspects.

Can overwatering cause brown spots?
Yes, indirectly. Overwatering stresses roots and creates a humid environment that encourages fungal diseases like blight, which cause brown spots.

How do you treat brown spots on tomato leaves?
First, identify the cause. Remove badly infected leaves. Improve air circulation and watering habits. For fungal issues, an organic fungicide like copper or a synthetic one like chlorothalonil can help protect healthy growth.

Should I remove leaves with brown spots?
Yes, carefully remove and dispose of severely spotted leaves. This improves air flow and reduces the source of new spores. Don’t remove to many, as leaves are the plant’s energy factory.

Why are there brown spots on my tomato stems?
Brown spots or cankers on stems can be a sign of Early Blight, Late Blight, or bacterial diseases. It’s often a sign of a more advanced infection. Check the rest of the plant closely and consider removing it if the problem is widespread.

Figuring out what causes brown spots on tomatoes takes a little detective work. By observing carefully and acting quickly with the right cultural practices, you can often save your crop and have a much healthier garden next year. Remember, consistent care and good sanitation are the most powerful tools you have.