What Blight Looks Like on Tomato Leaves and Stems

Early blight starts as small brown spots with concentric rings—like a target—on the lowest leaves of your plant. These spots are usually less than half an inch across and have a tan or dark brown center surrounded by a yellow halo. As the disease spreads, the rings become more obvious, and the entire leaf may yellow and drop off within days.

Late blight looks different: it appears as water-soaked, greasy-looking patches on leaves, often starting at the leaf edges or tips. The spots are usually larger and less defined than early blight spots. On the underside of the leaf, you may see a white, powdery coating—this is the fungal spores. Stems develop dark, sunken lesions that can girdle the plant and cut off water flow.

Both types of blight can spread to fruit. On tomatoes, you'll see dark, sunken patches that look like the fruit is rotting from the outside in. The fruit becomes inedible even if the rot hasn't reached the center yet.

Key Takeaways

  • Early blight shows up as small brown spots with concentric rings and a yellow halo, starting on lower leaves first.
  • Late blight appears as water-soaked, greasy patches with a white powdery coating on the leaf underside, and spreads much faster than early blight.
  • Both types can move to the fruit and stems, creating dark, sunken patches that make tomatoes unusable.
  • Blight spreads through water splash and humid air, so wet leaves and crowded plants are the biggest risk factors.

When Blight Appears During the Growing Season

Early blight typically shows up in mid to late summer, once your plants are established and the lower leaves have been exposed to soil splash for weeks. You'll usually notice it in July or August in most regions, though it can appear earlier in wet springs.

Late blight is the more aggressive threat and can strike at any point once temperatures drop below 75°F and humidity stays high. It spreads fastest in cool, wet weather—spring in warm climates and late summer in cooler ones. Late blight can destroy a healthy plant in three to five days once it takes hold, so speed matters when you spot it.

Where Blight Starts on the Plant

Early blight almost always begins on the lowest leaves, the ones closest to the soil. This is because soil splash carries the fungal spores up onto the foliage. If you see those telltale rings on a lower leaf, check the rest of the plant when ready—the disease is already established.

Late blight can start anywhere on the plant but often appears first on the newest growth at the top, since the fungus spreads through the air rather than soil splash. It can also start on the stem and work its way down. Check both the top and bottom of leaves, since the white spore coating on the underside is often the first sign you'll catch.

How to Tell Blight Apart from Other Tomato Problems

Yellowing leaves alone are not blight—that's usually nitrogen deficiency or normal aging. Blight always includes spots or patches with defined edges, not just color change. Early blight spots have that distinctive target pattern; if you see concentric rings, you have early blight. If the rings are absent and the spots are larger and water-soaked, suspect late blight.

Septoria leaf spot, another common tomato disease, creates small circular spots with dark borders and gray centers—but no rings and no yellow halo. Powdery mildew looks like a white dust on leaves but doesn't create the water-soaked patches or stem lesions that late blight does. When in doubt, look for the combination of spots plus a yellow halo (early blight) or water-soaked patches plus white spore coating on the leaf back (late blight).

What Happens if You Don't Treat Blight

Early blight spreads slowly at first—you might have a week or two before it moves beyond the lower leaves. If you remove infected leaves and improve air circulation, you can often slow it enough to harvest most of your crop. Left untreated, it will eventually defoliate the plant, exposing the fruit to sunscald and stopping the plant from producing new tomatoes.

Late blight is far more serious. It can move from a few spotted leaves to the entire plant in days. Once the stems are infected, the plant often collapses and dies. Late blight can also spread to nearby plants and overwinter in soil, making it a threat to next year's garden. If you see late blight, removing infected leaves when ready and improving drainage around the plant are your first moves.

Environmental Conditions That Trigger Blight

Both types of blight thrive in wet conditions. Overhead watering that wets the leaves creates the perfect environment for spores to germinate. Water the soil at the base of the plant instead, and water in the morning so any splash dries quickly. Crowded plants with poor air circulation trap humidity around the leaves—space your tomatoes at least 24 inches apart and prune lower branches to improve airflow.

Temperature matters too. Early blight prefers warm, wet weather (65–75°F). Late blight strikes in cooler, humid conditions (below 75°F). In regions with frequent rain or high humidity, blight is nearly inevitable without prevention. Mulching around the base of the plant keeps soil from splashing up onto leaves, which stops early blight spores from reaching the foliage in the first place.

Frequently Asked Questions

Can I eat a tomato with blight spots on it?

No. If blight has reached the fruit, the fungus has invaded the tissue. Even if you cut away the visible spot, the spores have likely spread into the fruit. Discard any tomato with blight lesions. Tomatoes with only leaf damage are safe to harvest and eat.

Does blight kill the whole plant or just the leaves?

Early blight usually stays on the leaves and stems, though it can eventually defoliate the plant and stop it from producing. Late blight is more aggressive and can kill the entire plant, including the stem, within a week. Both types can end your harvest if left untreated.

If I see blight on one leaf, should I remove the whole plant?

Not when ready. If it's early blight on a single lower leaf, remove that leaf and the ones directly above it, then monitor closely. If it's late blight, remove the infected leaf and watch for new spots daily—late blight spreads fast, so you may need to pull the plant if new spots appear within 48 hours.

Can I prevent blight by spraying my plants?

Preventive sprays with copper or sulfur can reduce blight risk if applied before the disease appears, but they don't stop it once infection starts. Spacing plants well, watering at soil level, and removing lower leaves as the plant grows are more reliable than sprays for most home gardeners.

Will blight come back next year if I plant tomatoes in the same spot?

Late blight can overwinter in soil and plant debris, so remove all infected plant material and don't compost it. Early blight spores survive in soil too. Rotating your tomato bed to a different location each year, or replacing the top 6 inches of soil, reduces the risk of both diseases returning.