What Causes Black Spots On Tomatoes

If you’ve ever grown tomatoes, you’ve probably seen black spots on them. Understanding what causes black spots on tomatoes is the first step to a healthy harvest. These marks can be frustrating, but they are usually a sign of specific issues you can fix. Let’s look at the common culprits and how you can deal with them.

Black spots on your tomatoes typically come from three main sources: fungal or bacterial diseases, environmental stress, or pest damage. The appearance and location of the spot give you the best clue. Some problems affect the fruit, while others start on the leaves. Correct identification is key to choosing the right solution.

1. Fungal and Bacterial Diseases

These are the most frequent causes of black spots. They spread easily, especially in warm, wet weather.

Early Blight

Early blight is a common fungal disease. It starts as small, dark spots on the lower, older leaves. The spots often have concentric rings, like a target. Leaves turn yellow and die. Fruit can develop dark, leathery spots at the stem end.

Cause: The fungus Alternaria solani.
Favors: Warm, humid conditions with rain.
Solution: Remove affected leaves. Improve air flow. Use a fungicide labeled for early blight.

Late Blight

Late blight is a serious, fast-moving disease. It causes irregular, greasy-looking gray or black spots on leaves and stems. Fruit develop firm, brownish-black spots. This disease can wipe out plants quickly.

Cause: The water mold Phytophthora infestans.
Favors: Cool, wet weather.
Solution: Remove and destroy entire infected plants immediately. Do not compost them. Preventive fungicides are often necessary in humid regions.

Bacterial Spot

This disease creates small, water-soaked spots on leaves and fruit. The spots on fruit become slightly raised and scabby, turning dark brown or black. Leaves may get ragged holes.

Cause: Bacteria (Xanthomonas species).
Favors: Warm, rainy, and windy weather.
Solution: Copper-based sprays can help prevent spread. Remove affected plant parts. Avoid overhead watering.

Anthracnose

Anthracnose appears on ripe or ripening fruit as small, sunken, circular spots. The spots darken and may develop a concentric pattern. It’s most common on overripe fruit touching the soil.

Cause: Several Colletotrichum fungi.
Favors: Warm, humid weather.
Solution: Harvest fruit promptly. Use mulch to prevent soil splash. Ensure good plant spacing.

2. Environmental and Physiological Problems

Not all black spots are from dieases. Sometimes, the plants environment causes the issue.

Blossom End Rot

This is a very common problem, but it’s not a disease. It starts as a water-soaked spot at the blossom end (bottom) of the fruit. The spot enlarges, turns dark brown or black, and becomes leathery. It’s caused by a calcium deficiency in the developing fruit, often due to irregular watering.

Cause: Low calcium in fruit tissue, usually from uneven soil moisture.
Favors: Fluctuating dry/wet cycles in soil.
Solution: Water deeply and consistently. Mulch heavily to retain moisture. Avoid excessive high-nitrogen fertilizer.

Sunscald

Sunscald happens when fruit is exposed to direct, intense sunlight. It starts as a white or yellow patch that becomes thin, wrinkled, and papery. The area can then turn black as secondary fungi move in.

Cause: Overexposure to sun, often after leaf loss from disease or pruning.
Favors: Hot, sunny weather with inadequate leaf cover.
Solution: Avoid over-pruning. Maintain healthy foliage to shade fruit. Use shade cloth in extreme heat.

3. Pest-Related Damage

Insects can create wounds that lead to black spots.

Stink Bug and Other Bug Damage

Piercing-sucking insects like stink bugs feed on the fruit. They insert their mouthparts, leaving tiny pinpricks. These spots may be yellow at first but develop into black, cloudy areas underneath the skin.

Cause: Insect feeding wounds.
Solution: Hand-pick pests. Use row covers early in season. Keep garden clean of debris where bugs hide.

Step-by-Step Guide to Diagnosis and Prevention

Follow these steps to figure out your problem and stop it next year.

Step 1: Examine the Spot Carefully

Look at the leaves. Are they spotted, yellowing, or wilting?
Check the spot’s location on the fruit. Is it at the blossom end, sides, or stem end?
Note the texture. Is it sunken, raised, scabby, or leathery?
Check the weather history. Has it been wet, dry, or very hot?

Step 2: Immediate Action to Take

Remove and destroy badly infected plant parts or fruit. For serious diseases like late blight, remove the whole plant.
Do not compost diseased material unless your pile gets very hot.
Apply appropriate treatment, like a fungicide or adjusting your watering.
Sterilize your pruning shears between cuts with a bleach solution.

Step 3: Long-Term Prevention Strategies

Prevention is always easier than cure. Here’s how to build a resilient garden:

Choose Resistant Varieties: Look for tomato varieties with codes like “EB” (Early Blight resistant) or “LB” (Late Blight resistant) on the tag.
Rotate Crops: Don’t plant tomatoes, potatoes, peppers, or eggplants in the same spot for at least 3 years.
Water Smartly: Water at the base of the plant, not overhead. Use soaker hoses or drip irrigation. Water deeply and consistently, especially once fruit is set.
Provide Space and Support: Space plants properly for good air circulation. Use cages or stakes to keep foliage and fruit off the ground.
Mulch Generously: Apply a 2-3 inch layer of straw or wood chips. This prevents soil-borne spores from splashing onto leaves and helps keep soil moisture even.
Fertilize Correctly: Get a soil test. Avoid too much nitrogen, which makes lush leaves prone to disease. Use a balanced or tomato-specific fertilizer.

What to Do with Affected Tomatoes

You can often salvage part of your harvest. For disease spots like anthracnose, you can cut out the small, sunken spot and the rest of the tomato is fine to eat. For blossom end rot, simply cut off the blackened portion. However, if the fruit is rotten, soft, or smells bad, it’s best to toss it in the trash, not the compost. Never eat fruit with mold on it.

FAQ Section

Are tomatoes with black spots safe to eat?
It depends on the cause. If it’s blossom end rot or a small fungal spot you can cut away, the rest is safe. Do not eat fruit that is rotted, moldy, or smells off.

How do you treat black spots on tomato leaves?
First, identify the disease. Remove affected leaves. Improve air flow. For fungal issues, an organic fungicide like copper spray or chlorothalonil can help prevent further spread if applied early.

What is the best fungicide for tomato black spots?
For early blight and anthracnose, chlorothalonil is a common effective option. For bacterial spot, copper-based sprays are used. Always follow the label instructions carefully.

Can overwatering cause black spots?
Indirectly, yes. Overwatering creates humid conditions that fungi love and can lead to root rot, stressing the plant. It also contributes to blossom end rot by preventing calcium uptake.

Why are my tomato seedlings getting black spots?
Seedlings often suffer from “damping off,” a fungal disease that blackens stems at the soil line. Ensure they have excellent air circulation, well-draining soil, and are not overwatered.

Dealing with black spots on tomatoes is part of the gardening journey. By observing closely and acting quickly, you can manage most problems. Focus on building healthy soil and consistent habits. Your efforts will be rewarded with a stronger, more productive garden each season.