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Early Blight

Early Blight

Alternaria solani, Alternaria tomatophila

Fungalalso: Alternaria leaf blight

A very common fungal disease of tomato and potato that shows up nearly every season. It starts on the oldest, lowest leaves as brown spots with target-like rings and works its way up the plant, stripping foliage and exposing fruit. A small amount is normal late in the season, but an early, heavy case can sharply reduce yield.

🔎 How to spot it

Look for round brown to black leaf spots up to half an inch across with dark concentric rings that look like a target or bullseye, usually ringed by a yellow halo. Spots appear first on the oldest leaves near the ground. On stems they form oval dark sunken lesions, and on fruit they appear as leathery black sunken patches with concentric ridges near the stem end. Affected leaves yellow, brown, and drop.

🥀 Damage it causes

Infected leaves yellow and fall, working upward until the plant is badly defoliated. Loss of leaf cover stresses the plant, lowers yield, and exposes fruit to sunscald. Seedlings can be girdled at the soil line by collar rot and die. Fruit lesions make the fruit unusable.

🔬 What causes it

Early blight is caused by the fungi Alternaria solani and Alternaria tomatophila, which overwinter in infected plant debris and soil and can ride in on seed or transplants. The fungus is splashed onto the lowest leaves by rain and irrigation. Disease develops in moderate to warm weather, from about 59 to 80 F, and is worst with wet weather, heavy dew, or humidity above 90 percent.

🛡️ Prevent it

Rotate tomatoes and potatoes to a new spot on a two to three year cycle. Mulch under plants to block soil splash, water at the base with drip or a soaker hose rather than overhead, and space, stake, or cage plants for airflow. Prune off the lowest leaves so they do not touch the soil. Choose resistant or tolerant varieties and remove crop debris at season end.

🧯 If it is already here

Remove and destroy infected leaves as soon as they appear and sanitize your tools. Keep the foliage dry and the lower leaves pruned. Home gardeners rarely need to spray, but protective organic fungicides such as copper or a Bacillus subtilis biofungicide, applied early and repeated, can slow spread. Resistant varieties reduce severity but do not give complete control.

💡 Good to know

Early blight occurs nearly every season wherever tomatoes and potatoes are grown, so the goal is to slow it, not eliminate it. It is easy to confuse with Septoria leaf spot, but early blight spots are larger with target rings, while Septoria spots are smaller with tan centers and tiny black dots. Both start on the lowest leaves after fruit set.

🌱 Plants it affects

72 plants in the library can be affected by this problem

Adirondack Blue PotatoAji Amarillo Pepper🥔All Blue PotatoAmish Paste TomatoAnaheim PepperBanana PepperBeauregard Sweet Potato🍅Beefmaster TomatoBetter Boy Tomato🍅Big Beef TomatoBig Boy TomatoBlack Beauty EggplantBlack Cherry TomatoBlack Krim Tomato🍅Box Car Willie TomatoBrandywine TomatoCarolina Reaper PepperCayenne PepperCelebrity TomatoCherokee Purple TomatoCosmic Purple CarrotCubanelle PepperEarly Girl TomatoFairy Tale EggplantFingerling PotatoFresno PepperGerman Butterball Potato🍅German Queen TomatoGhost PepperGreen Bell PepperGreen Zebra TomatoHabanero PepperHungarian Wax PepperIndigo Rose TomatoItalian EggplantJalapeño PepperJapanese EggplantJuliet Grape TomatoKellogg's Breakfast TomatoKennebec Potato🍅La Roma IV TomatoLemon Boy Tomato🍅Mortgage Lifter TomatoMr. Stripey TomatoNorland PotatoOrange Bell PepperPadrón PepperPimento PepperPineapple TomatoPoblano PepperPurple Bell Pepper🥔Purple Majesty PotatoRed Bell PepperRed Pontiac PotatoRoma Tomato🍆Rosa Bianca EggplantRusset Potato🍅Rutgers TomatoSan Marzano TomatoScotch Bonnet PepperSerrano PepperShishito Pepper🍅Striped German Tomato🍅Sungold Cherry TomatoSweet 100 Cherry TomatoSweet Banana PepperThai Chili Pepper🍅Tiny Tim Cherry TomatoTrinidad Scorpion PepperYellow Bell PepperYellow Pear TomatoYukon Gold Potato

For educational and informational purposes only. Disease management advice is general guidance drawn from university cooperative extension sources; always identify a problem positively and read and follow the label on any product before use, especially around food crops, children, and pets.