Angular leaf spot
Angular, brown spots bounded by the leaf veins in a distinctive "stained-glass" pattern, with a grey fungal growth on the underside in humid weather — heavy spotting causes early leaf drop and cuts pod fill.
- Pathogen
- Fungus (Pseudocercospora griseola)
- Spreads by
- Wind and rain splash; infected seed and debris
- Favoured by
- Warm, humid conditions; dense stands
- Main risk
- Early leaf drop cutting pod fill and yield
Overview
Angular leaf spot is caused by the fungus Pseudocercospora griseola, a leaf-spot disease of French bean and related beans that gets its name from the distinctive angular shape of its lesions — bounded on all sides by the fine veins of the leaf, giving a mosaic or "stained-glass" appearance rather than the round spots typical of many other leaf diseases.
In humid weather a fine grey fungal growth develops on the underside of the spots, which is where the fungus produces the spores that spread it further. Heavy infection causes the spots to merge, yellows and browns large areas of the leaf, and brings on early leaf drop — which directly cuts the leaf area driving pod fill and lowers yield, especially when infection builds up during flowering and pod development.
How to identify it
- Angular, brown spots on leaves, sharply bounded by the fine veins — a distinctive mosaic or "stained-glass" pattern.
- A fine grey fungal growth on the underside of spots in humid weather.
- Spots merging into larger dead patches as infection builds, followed by yellowing and early leaf drop.
- Can also appear as small lesions on pods in a heavy attack, though leaves are affected first and worst.
What causes it and when
- The fungus Pseudocercospora griseola, spread by wind and rain splash between plants and fields.
- Favoured by warm, humid conditions and dense, poorly-ventilated stands where leaves stay wet for long periods.
- Can be carried on infected seed and in crop debris left in the field after harvest.
Cultural & organic control
- Choose a variety with documented resistance where available (Pant Anupama, for humid hill/tarai conditions) rather than a susceptible one on land with a history of the disease.
- Sow with wider spacing for better airflow, and avoid overhead irrigation late in the day so foliage dries before nightfall.
- Rotate away from French bean and other beans for a season or two on an infected field, and clear and destroy crop debris after harvest.
Chemical control
- A protective fungicide such as mancozeb from the first spots, repeated at 10–14 day intervals in wet weather, observing the pre-harvest interval since pods are picked every 2–3 days.
- Confirm the current recommended product and dose for your area with your local KVK.
Prevent it coming back
- Use certified seed and a resistant variety on fields with a history of the disease.
- Keep the canopy open with adequate spacing and avoid working in wet foliage, which spreads spores on hands and tools.
- Clear and destroy infected residue after harvest rather than leaving it to carry the fungus into the next crop.
Crops most at risk
Where this problem is called out in our crop guides — open a crop for the full package of practices.
Varieties to consider
Named seed varieties whose resistance or susceptibility to this problem is documented on their own variety page.
Frequently asked questions
How is angular leaf spot different from the other brown spots I see on French bean leaves?
Its defining feature is the sharp, angular shape of each spot, bounded on all sides by the fine leaf veins, giving a mosaic or "stained-glass" look — round or irregular spots without that boundary are more likely a different disease such as anthracnose or Cercospora leaf spot. In humid weather, checking the underside of a spot for a fine grey fungal growth helps confirm it.
Is there a French bean variety resistant to this disease?
Pant Anupama, bred by GBPUAT, Pantnagar, carries documented resistance to angular leaf spot along with common bacterial blight and mosaic virus, and is a strong choice specifically for the humid hill and tarai belt where this disease is common.
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.