Early blight on tomatoes

Early blight is the most common foliage disease of tomatoes in the eastern US, and in most summers it is also inevitable. Nearly every tomato planting shows some early blight by late July or August, even with good management. The practical goal is not elimination -- it is slowing the rate of.

—- title: "Early blight on tomatoes" slug: early-blight-on-tomatoes hub: problems category: "Disease-by-host" description: "Early blight defoliates tomatoes from the bottom up every summer. Identify the target-spot lesions, apply mulch and fungicides at the right time, and understand why some years are worse than others." date: 2026-06-10 updated: 2026-06-10 author: "Thomas A." reading_time: 8 —-

Early blight is the most common foliage disease of tomatoes in the eastern US, and in most summers it is also inevitable. Nearly every tomato planting shows some early blight by late July or August, even with good management. The practical goal is not elimination — it is slowing the rate of defoliation enough that plants continue producing fruit through the season.

I don't grow tomatoes at my Long Island property, so this guide draws on University Extension research.

The pathogen

Early blight is caused by Alternaria solani. Per Cornell Cooperative Extension, the fungus overwinters in infected plant debris in soil and on seeds. Conidia (spores) are produced on infected tissue and splash-dispersed from soil and lower leaves onto upper foliage. The disease is favored by warm temperatures (75–85°F, 24–29°C) with intermittent wet periods, which describes most of the tomato-growing summer in the mid-Atlantic.

Note: Alternaria solani also causes early blight on potatoes (see Early blight on potatoes), but tomato and potato strains are closely related and management is similar.

Identification

Leaf lesions

Per Penn State Extension, the characteristic lesion is:

• Target spot pattern — concentric rings of lighter and darker brown tissue creating a bull's-eye appearance, 0.25–0.5 inch in diameter
• Angular to oval outline — lesions often have a slightly irregular edge
• Yellow halo — a chlorotic (yellow) ring often surrounds the lesion, a plant response to the fungal toxins
• Lower leaf location — early blight progresses from the oldest (lowest) leaves upward; the tops of healthy plants remain green while the base browns and defoliates

Stem and fruit symptoms

Per Cornell Cooperative Extension, A. solani can also infect:

• Stems — dark, sunken lesions on stem tissue, particularly at the soil line (collar rot)
• Fruit — dark, leathery, sunken lesions at the stem end with concentric rings; less common than foliar symptoms but can occur late in the season on fruit in contact with infected foliage

Distinguishing from Septoria leaf spot

Per Clemson HGIC, Septoria leaf spot (Septoria lycopersici) also starts on lower leaves and progresses upward, but its lesions are smaller (0.1–0.25 inch), circular, with tan-gray centers and dark borders — no target-spot rings. Tiny black dots (pycnidia) are visible in Septoria lesion centers under magnification. Early blight lesions are larger, have the concentric ring pattern, and lack the central dots.

Both diseases can occur simultaneously on the same plant.

Disease cycle

Per Penn State Extension:

1. The pathogen survives in infected plant debris in soil
2. Rain or irrigation splashes conidia from soil onto lower leaves
3. Leaf infection occurs when temperatures are 75–85°F (24–29°C) and leaves are wet for 1–2 hours
4. Lesions produce secondary conidia that infect progressively higher leaves as the season progresses
5. Warm, wet weather in July and August accelerates the upward progression

Plant stress amplifies the disease

Per Cornell Cooperative Extension, early blight progresses faster on stressed plants. Nitrogen deficiency, water stress, and other diseases that weaken plants accelerate early blight progression. A well-fertilized, consistently watered tomato plant in good health will show later and slower early blight progression than a stressed plant.

Management

Mulching

Per Penn State Extension, applying 2–3 inches of organic mulch (straw, wood chips) under plants reduces soil splash of conidia onto lower leaves. This is the most consistently effective single management step. Apply at transplant time, before disease pressure begins.

Remove lower leaves

Per Clemson HGIC, removing the lowest 12 inches of foliage — the leaves nearest the soil surface — in early July eliminates the primary infection sites and reduces the spore load available for upward spread. Remove leaves that show lesions first. Carry removed leaves off-site rather than leaving them on the soil.

Crop rotation and residue management

Per Cornell Cooperative Extension, rotate tomatoes and potatoes to different beds on a 2–3 year cycle and remove all plant debris at season's end. The pathogen survives in intact residue; thorough cleanup reduces the starting inoculum the following season.

Avoid overhead irrigation

Per Penn State Extension, drip or soaker hose irrigation eliminates the leaf-wetness events that trigger infection. Overhead irrigation in the afternoon creates leaf wetness that persists overnight — prime infection conditions. Water in the morning if overhead irrigation is necessary.

Fungicides

Per Penn State Extension, preventive fungicide applications reduce early blight severity when begun before symptoms appear or at first symptom. Begin applications when plants are 12 inches tall or at first sign of disease, repeating every 7–10 days during warm, wet weather. Registered active ingredients:

• Chlorothalonil — broad-spectrum protectant; widely available
• Mancozeb — effective protectant; observe pre-harvest intervals
• Copper-based fungicides — OMRI-listed for organic production
• Azoxystrobin (group 11 strobilurin) — systemic; resistance documented in some populations; rotate with other modes of action

Per Clemson HGIC, fungicides protect healthy tissue from new infections; they do not restore destroyed leaves.

Resistant varieties

Per Cornell Cooperative Extension, some varieties have better early blight tolerance than others. 'Mountain Supreme' and 'Juliet' (cherry) show better tolerance in NC State and Cornell trials. No variety is immune, but tolerant varieties maintain green canopy later into the season under disease pressure.

Common problems table

Frequently Asked Questions

Does early blight kill tomato plants?

Per Penn State Extension, early blight rarely kills established tomato plants outright. It reduces yield by defoliating plants progressively, limiting photosynthesis. Plants often remain alive and productive through severe defoliation, though fruit quality and quantity are reduced.

Is early blight the same as late blight?

Per Cornell Cooperative Extension, no. Early blight is caused by Alternaria solani; late blight is caused by Phytophthora infestans (an oomycete). They produce different lesion types and require different fungicides. Early blight produces target-spot lesions on lower leaves; late blight produces large, water-soaked, fast-spreading lesions that can kill plants within days. See Late blight on tomatoes for comparison.

What year does early blight appear for the first time in a new garden?

Per Clemson HGIC, early blight is endemic in most soils that have grown tomatoes or potatoes. In a genuinely new garden space with no prior solanaceous crops, the first year may show less disease, but spores can arrive via wind and rain from nearby sources. Expect some disease in most years once you are growing tomatoes.

Should I pull up badly defoliated plants?

Per Penn State Extension, if a plant retains any productive foliage and has fruit in development, leaving it in place until the first frost or until it has no remaining healthy tissue is usually more productive than removal. Plants compensate for foliage loss with residual capacity if the defoliation is not complete.

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Sources

1. Cornell Cooperative Extension — Early Blight of Tomato
2. Penn State Extension — Early Blight of Tomato
3. Clemson HGIC — Tomato Diseases and Other Problems