What Blight Looks Like on Tomato Leaves and Stems
Blight appears as dark, water-soaked spots that start small and spread outward in concentric rings, usually beginning on the lower leaves of your tomato plant. Early blight, the most common type, shows brown spots with a target-like pattern—lighter rings alternating with darker ones. Late blight looks different: it starts as pale green or grayish spots on leaves, often with a white mold-like coating on the underside, and spreads much faster than early blight.
On stems and branches, blight creates elongated lesions that can girdle the stem and cut off water flow to the plant above that point. The affected tissue becomes papery and may crack open. If you see yellowing leaves below the spotted area, that is a sign the disease is blocking nutrients from moving up the plant.
The key difference between blight and other tomato diseases is the pattern and speed. Blight spots have defined edges and a deliberate appearance, not the fuzzy or powdery look of fungal mildew. Early blight progresses slowly over weeks; late blight can destroy a plant in days.
Key Takeaways
- Early blight shows brown spots with concentric rings on lower leaves, while late blight appears as pale green spots with white mold underneath.
- Blight spots have clear, defined edges and often form a target pattern, which separates them from powdery mildew or other leaf diseases.
- The disease spreads upward from the bottom of the plant first, so check lower leaves before upper growth.
- Wet conditions and poor air circulation make blight spread faster, so the pattern you see depends partly on your watering and spacing habits.
Early Blight: Brown Rings and Gradual Spread
Early blight starts on the oldest leaves at the base of the plant and works its way up over the course of several weeks. The first sign is a small brown spot, usually less than a quarter inch across. Within a few days, that spot develops the characteristic target pattern—alternating rings of brown and tan that look like a bullseye.
As the disease progresses, the entire leaf yellows around the spotted area, then the leaf drops off. You will lose leaves gradually, starting from the bottom, which is why the plant looks progressively more bare at the base while the top stays green. The spots themselves stay relatively small, rarely larger than half an inch, but they multiply across the leaf surface.
Early blight thrives in warm, wet conditions—typically between 60 and 80 degrees Fahrenheit with high humidity or frequent watering. If you water from above or the plant sits in morning dew for hours, you are creating the exact environment the disease needs. Soil splash from rain or watering spreads spores from the ground to the lower leaves, which is why the disease always starts low.
Late Blight: Pale Spots and Rapid Destruction
Late blight is the more aggressive disease and the one that caused the Irish potato famine in the 1840s. It looks completely different from early blight: the spots start pale green or grayish, not brown, and they lack the concentric rings. The spots often have an irregular shape and may have a water-soaked appearance, as if the leaf is rotting from the inside.
The underside of the leaf is the giveaway. Look there and you will see a white or grayish mold-like coating, which is actually millions of spores. This coating spreads quickly and can cover an entire leaf in a few days. The leaf then turns brown and papery and falls off. Unlike early blight, late blight can destroy a healthy plant in a week or less, especially in cool, wet weather.
Late blight spreads through the air as well as through soil splash, which is why it moves so fast. A single infected plant can infect your entire garden. The disease prefers temperatures between 60 and 70 degrees Fahrenheit and thrives during rainy periods or when humidity stays above 90 percent for extended hours.
Where Blight Appears First and How It Spreads
Blight always starts on the lower leaves because that is where moisture collects and where soil-borne spores land. If you see spots on the top of the plant but the bottom looks clean, you are probably looking at a different disease. With blight, the bottom is always affected first.
The disease spreads upward as the spores move from leaf to leaf, usually following the path of water. If you water from above, you are actively spreading spores upward. If you water at the soil level and keep the foliage dry, you slow the spread significantly. Wind also carries late blight spores, so a plant downwind of an infected neighbor's garden can catch the disease even if you have never touched it.
Once blight reaches the fruit, the spots appear as dark, sunken lesions that start small and expand. The fruit becomes inedible. Fruit infection is less common than leaf infection, but it happens when spores land directly on the tomato or when rain splashes spores upward from infected leaves.
Blight Versus Other Common Tomato Leaf Problems
Septoria leaf spot, another common tomato disease, looks similar to early blight but has smaller spots—usually the size of a pinhead—with a dark border and a gray center with tiny black dots. The spots do not have the concentric rings of blight. Septoria also starts on lower leaves but spreads more slowly.
Powdery mildew appears as a white, dusty coating on leaves, usually on the upper surface, and does not create the defined brown spots that blight does. Fusarium wilt causes yellowing and wilting but no spots at all. Sunscald creates pale, papery patches on fruit exposed to direct sun, not on leaves.
The surest way to tell blight from other diseases is the target pattern on early blight and the white mold coating on the underside of leaves with late blight. If you see those two signs, you have blight. If you see something else, you are dealing with a different problem that may need a different solution.
Environmental Conditions That Make Blight Visible
Blight symptoms show up faster and spread more visibly when conditions favor the disease. Heavy rain, overhead watering, and high humidity all accelerate the appearance of spots and the progression of the disease. If you have had a wet week, check your plants carefully—blight may be further along than you think.
Cool nights combined with warm days also speed up blight development. A stretch of weather in the 60s and 70s with high moisture is ideal for the fungus. In hot, dry climates, blight is rare because the spores cannot germinate without moisture on the leaf surface for at least several hours.
Poor air circulation makes blight worse because leaves stay wet longer after rain or watering. Plants crowded together, planted too close to walls or fences, or surrounded by tall weeds all develop blight faster than plants with good airflow. If you can see the disease spreading quickly, the first thing to check is whether water is sitting on the leaves.
Frequently Asked Questions
Can I eat tomatoes from a plant with blight?
Tomatoes on the plant are safe to eat if the fruit itself has no spots. The disease affects leaves and stems, not the inside of the fruit. Harvest any ripe or nearly ripe tomatoes before the disease gets worse, and wash them before eating. Do not compost infected leaves or stems—throw them in the trash.
Does blight always start on the bottom leaves?
Early blight almost always starts on the lowest leaves because soil splash carries spores upward. Late blight can start anywhere on the plant if spores land there, but it still spreads fastest on lower, more humid leaves. If you see spots only on the top of the plant, you may be looking at a different disease.
How fast does late blight spread compared to early blight?
Early blight takes weeks to defoliate a plant. Late blight can destroy the entire plant in five to seven days under wet conditions. Late blight also spreads through the air, while early blight spreads mainly through soil splash and direct contact. This is why late blight is considered the more dangerous of the two.
What does the white coating on the underside of leaves mean?
That white coating is the spore-producing structure of the late blight fungus. It is a sign the disease is actively reproducing and spreading. If you see it, the plant is highly contagious to other tomatoes nearby. Remove the affected leaves when ready and dispose of them in the trash, not the compost.
Can blight spread to other plants in my garden?
Early blight spreads mainly through soil splash and direct contact, so it can spread to other tomatoes if you touch them after handling an infected plant. Late blight spreads through the air, so it can reach potatoes, peppers, and other tomatoes downwind. Wash your hands and tools after handling infected plants to prevent spread.