The three diseases that cause black spots on tomato leaves and fruit

Black spots on tomato plants almost always come from one of three fungal diseases: early blight, late blight, or septoria leaf spot. Early blight starts on the lowest leaves as small dark circles with concentric rings (like a target), then spreads upward as the plant grows. Late blight looks similar but moves much faster and can kill a plant in days—it also spots the fruit itself, not just leaves. Septoria leaf spot creates tiny dark specks with gray centers and a dark border, and the spots are smaller and more numerous than early blight.

All three are caused by fungi that live in soil and plant debris, spread by water splash and humidity, and thrive in warm, wet conditions. The difference matters because the treatment changes depending on which one you have. Early blight and septoria are slow and manageable; late blight is an emergency.

Key Takeaways

  • Early blight appears first on lower leaves as target-shaped rings and spreads upward; late blight moves fast, spots fruit, and can kill a plant within days.
  • All three diseases spread through water splash and high humidity, so watering at soil level (not overhead) and spacing plants for air flow are the strongest prevention steps.
  • Removing infected leaves as soon as you see spots stops the disease from moving up the plant and reduces spores in your garden.
  • Fungicide sprays work best as prevention before spots appear, not as a cure after infection; copper and sulfur are common organic options.
  • If late blight appears, remove the entire plant when ready—it spreads too fast to save with pruning or spraying.

Why humidity and water splash create the perfect conditions

Fungal spores need moisture to germinate and infect leaves. When you water overhead with a sprinkler or hose, you create exactly the wet leaf surface these fungi need. Water sitting on a leaf for even a few hours in warm weather gives spores time to break through the leaf's outer layer and establish infection.

The same happens during rain or heavy morning dew. Soil splashing up onto the lowest leaves during a storm carries spores from the ground directly onto the plant. This is why early blight always starts at the bottom—those lower leaves are closest to the soil where the fungus lives.

High humidity (above 85 percent) without direct water also favors these diseases. Crowded plants that don't get air flow trap moisture between leaves, creating a greenhouse effect that fungi love. A plant in full sun with space around it dries faster and resists infection better than one squeezed between neighbors.

How to prevent black spots before they start

The strongest prevention is changing how you water. Water at soil level only, early in the morning, so the soil has time to absorb water before the day heats up. Drip irrigation or soaker hoses are ideal because they wet only the soil, never the leaves. If you must use a sprinkler, run it in early morning so leaves dry quickly as the sun rises.

Space plants far enough apart that air moves freely between them. Tomatoes need at least 24 to 36 inches of space depending on the variety. Prune lower leaves once the plant is established—remove the bottom 6 to 12 inches of foliage, which are closest to soil splash and most vulnerable. Do this pruning in dry weather and wash your hands and tools afterward so you don't spread spores to other plants.

Remove fallen leaves and plant debris from the ground around your tomatoes. These are where the fungus overwinters and waits for next season. At the end of the season, pull the entire plant (don't leave it in the bed) and throw it away or burn it if your area allows it. Do not compost diseased plant material unless your compost reaches 140 degrees Fahrenheit, which most home piles do not.

What to do if you spot black marks on leaves

Act when ready. Pinch or cut off the affected leaf as soon as you see spots, removing the entire leaf at its stem. Do this in dry weather and dispose of the leaf in the trash, not the compost. Wash your hands and disinfect your pruners with rubbing alcohol or a 10 percent bleach solution (one part bleach to nine parts water) before touching another plant.

Remove all leaves below the lowest fruit cluster, even if they look healthy. These lower leaves are at highest risk and removing them improves air flow. Continue removing spotted leaves as they appear. On early blight and septoria, this pruning alone often stops the spread if you catch it early.

If the disease is spreading faster than you can prune, a fungicide spray may help. Copper fungicides and sulfur dust are organic options available at garden centers. Spray every 7 to 10 days starting when you first see spots, coating both the top and bottom of remaining leaves. Follow the label directions exactly—some fungicides damage tomatoes in heat above 85 degrees, and sulfur can burn leaves if applied within two weeks of an oil spray.

Late blight is different—remove the plant when ready

Late blight moves so fast that pruning and spraying usually fail. If you see spots that are spreading to new leaves within days, or if you see spots on the fruit itself, assume it is late blight and pull the entire plant out of the ground. Do not try to save it by removing leaves. Do not compost it. Bag it and throw it away, or burn it if your area allows it.

Late blight can wipe out a whole garden in a week if left unchecked. The fungus also infects potatoes, so if you grow potatoes nearby, check them when ready. If late blight appears, increase spacing and air flow on your remaining tomatoes, water only at soil level, and watch closely for any new spots. You may need to spray preventively with copper every 7 days for the rest of the season.

Choosing tomato varieties that resist disease

Some tomato varieties are bred to resist early blight, late blight, or septoria leaf spot. Look for varieties labeled with disease codes on the seed packet or plant label. The codes are usually letters: EB means early blight resistance, LB means late blight resistance, and S means septoria resistance. A plant labeled "EB LB S" resists all three.

Resistant varieties are not immune—they still get infected in severe conditions—but they slow the disease down and give you more time to manage it. If you live in a region where late blight is common (cool, wet summers in the Northeast and Pacific Northwest), choosing a resistant variety is one of your best defenses. Heirloom and open-pollinated varieties often have less resistance than modern hybrids, so if disease is a problem in your garden, hybrid varieties are worth trying.

When to call a professional or your local extension office

If you are not sure which disease you have, take a photo of the spotted leaf and contact your county extension office. They can identify the disease from a photo or a sample and recommend the best treatment for your region. Extension offices are free and exist specifically to help home gardeners solve plant problems.

If the disease spreads despite your efforts, or if it appears on multiple plants, a professional may be able to recommend a stronger fungicide or a different approach. Some regions have specific disease management guides for tomatoes that account for local weather patterns and which diseases are most common in your area.

Frequently Asked Questions

Can I eat tomatoes that have black spots on them?

If the spots are only on the leaves, the fruit is safe to eat. If the spots are on the fruit itself, cut out the spotted area and discard it—the fungus is only in the spotted tissue. Wash the tomato first. If more than a quarter of the fruit is spotted, discard the whole tomato.

Do I need to spray fungicide every week even if I don't see spots?

Preventive spraying is most useful if the disease appeared last year or if conditions are very humid. If your plants are healthy and you are watering at soil level with good air flow, you may not need to spray at all. Start spraying only when you see the first spots or when weather turns warm and wet.

Can I save a plant with late blight by removing all the leaves?

No. Late blight spreads through the plant's vascular system, not just on the leaves. Removing leaves will not stop it. Pull the plant and dispose of it to prevent the fungus from spreading to other plants in your garden.

What is the best time of year to plant tomatoes to avoid black spot diseases?

Plant early enough that tomatoes mature before late summer humidity peaks, but not so early that cool spring weather slows growth. In most regions, planting in late spring (after the last frost) gives you the best window. In areas with late blight pressure, some gardeners plant extra early to harvest before late summer rains arrive.

Does neem oil work on black spot fungus?

Neem oil is not effective against the fungi that cause black spots on tomatoes. Copper and sulfur are the most reliable organic options. Some gardeners also use baking soda spray (one tablespoon per gallon of water with a drop of dish soap), though it is less proven than copper or sulfur.