Early blight
Concentric "target-board" brown spots on the older leaves of potato and tomato that spread up the plant — and sink dark leathery spots into tomato fruit.
- Pathogen
- Fungus (Alternaria solani)
- Spreads by
- Wind & rain-splashed spores; debris
- Favoured by
- Warm, humid weather; stressed crop
- Main risk
- Bottom-up defoliation; fruit spots
Overview
Early blight (Alternaria solani) is a very common fungal disease of potato and tomato. It begins on the older, lower leaves as small dark-brown spots that enlarge into circular lesions marked with concentric rings — the classic "target-board" or bull’s-eye pattern — often ringed by a yellow halo.
As spots multiply the leaves yellow, dry and drop, and the disease climbs the plant, defoliating it from the bottom up and exposing potato tubers or tomato fruit to sunscald and lower yield. On tomato fruit it makes dark, sunken, leathery spots (usually at the stem end) with the same concentric rings. It is favoured by warm, humid weather with dew or light rain, and by stressed, poorly-nourished crops, and it carries over on infected debris and volunteer plants.
How to identify it
- Dark-brown circular spots with concentric rings (a "target-board" look), starting on the older, lower leaves.
- A yellow halo around the spots; as they merge, the leaf yellows, dries and drops, and the disease climbs the plant.
- In tomato, dark, sunken, leathery spots with concentric rings on the fruit, usually near the stem end.
- Bottom-up defoliation that exposes potato tubers/tomato fruit — distinct from late blight’s fast top-down collapse.
What causes it and when
- The fungus Alternaria solani, spread by wind- and rain-splashed spores and carried over on infected debris, volunteers and seed/tubers.
- Favoured by warm, humid weather with dew or light rain (a bit warmer and less wet than late blight).
- Worse on stressed, poorly-nourished or ageing crops — poor nitrogen and other stresses make plants more susceptible.
- Builds up through the season, so late-season crops and successive plantings are hit harder.
Cultural & organic control
- Grow resistant/tolerant varieties, use clean seed/tubers, and rotate away from potato/tomato (and other solanaceous crops).
- Keep the crop vigorous and well-nourished — a healthy, unstressed crop resists early blight far better.
- Give open spacing, stake tomatoes, and avoid overhead irrigation so foliage dries; mulch to stop soil-splash onto lower leaves.
- Remove and destroy infected lower leaves and crop debris, and control volunteer plants.
Chemical control
- Start protective sprays when the first spots appear on the lower leaves, before it climbs the plant.
- CIB&RC-registered fungicides for early blight — mancozeb and other protectants, plus recommended systemics — are used and rotated to avoid resistance.
- Cover the older/lower leaves well and observe the pre-harvest interval, especially on frequently-picked tomato.
- Confirm the current recommendation and rotation for your crop and area with your local KVK.
Prevent it coming back
- Use resistant varieties, clean seed/tubers and crop rotation, and destroy debris and volunteers that carry it over.
- Keep the crop well-nourished and unstressed, and manage spacing and irrigation for quick foliage drying.
- Scout the lower leaves from mid-season and act early, rotating fungicide groups.
Crops most at risk
Where this problem is called out in our crop guides — open a crop for the full package of practices.
Frequently asked questions
My potato/tomato leaves have brown spots with rings like a target. What is it?
Those concentric-ring, "target-board" brown spots on the older, lower leaves are early blight (Alternaria). It starts low and climbs the plant, drying the leaves, and on tomato it also makes dark sunken spots on the fruit. Start protective fungicide sprays at the first spots, keep the crop well-nourished, and remove infected lower leaves.
How is early blight different from late blight?
Early blight makes concentric-ring "target" spots on the older, lower leaves and spreads slowly bottom-up in warm, humid weather; the crop is stressed but not suddenly destroyed. Late blight is far more aggressive — water-soaked lesions with white mould underneath that can collapse the whole crop in a few days of cool, wet weather. They need different timing and fungicides.
Why does early blight hit stressed crops harder?
Alternaria solani is a weak pathogen that takes advantage of ageing, stressed or poorly-nourished tissue, so a crop short of nitrogen, drought-stressed or nearing maturity is much more susceptible. Keeping the crop vigorous and well-nourished — along with resistant varieties, rotation and timely protective sprays — is a real part of managing early blight.
Symptoms and control measures follow ICAR, KVK and state agricultural-university package-of-practices; any named chemical is a registered use. Always read the product label and confirm the dose for your crop and zone. editorial policy.