Angular leaf spot of bean

Pseudocercospora griseola Pseudocercospora griseola (Sacc.) Crous & U. Braun, 2006 · formerly or also: Phaeoisariopsis griseola, Isariopsis griseola

mancha angular · Spanish, Latin America
mancha-angular do feijoeiro · Portuguese, Brazil
taches anguleuses du haricot · French, France and Africa

Angular leaf spot covers bean leaves with grey to brown spots that are angular because they are bounded by the small veins. Underneath the spots, the fungus forms tiny dark tufts of spores. Leaves yellow and drop early, and pods develop reddish-brown spots. It is one of the most damaging bean diseases in the tropics and subtropics, especially in Africa and Latin America, where losses can reach half of the crop or more.

Microscope view of a spore-bearing tuft (synnema) of Pseudocercospora griseola, the angular leaf spot fungus. Photo: Meswaet Y, Mangelsdorff R, Yorou NS, Piepenbring M (MycoKeys 2021), CC BY 4.0, via Wikimedia Commons.

Type: Fungal disease · Fungus (ascomycete)
Classification: Fungi › Dothideomycetes › Mycosphaerellales › Mycosphaerellaceae
Main crops: Common bean, Green bean
Found in: Africa, Latin America, Asia, Europe and North America
Chemical groups: FRAC 3, FRAC 11, FRAC M05 (mode-of-action groups, not products)
Last reviewed: 2026-10-20

What causes angular leaf spot of bean?

Angular leaf spot of bean is caused by Pseudocercospora griseola Pseudocercospora griseola (Sacc.) Crous & U. Braun, 2006, a fungus (ascomycete) (order Mycosphaerellales, family Mycosphaerellaceae).

Older or alternative scientific names: Phaeoisariopsis griseola, Isariopsis griseola.

Where it occurs

Found in bean-growing areas worldwide, most damaging in warm, humid tropical and subtropical regions of Africa and Latin America, and also in Asia, Europe and North America.

Region	Status
Africa	Widespread; major in East and southern Africa
Latin America	Widespread
Asia	Present
Europe and North America	Present; usually less severe

Symptoms and identification of angular leaf spot of bean

The organism

A fungus that produces dark, bristle-like bundles of spore-bearing threads (synnemata) on the undersides of leaf spots and on pods. Pathogen populations are divided into Andean and Mesoamerican groups that match the two main gene pools of cultivated beans. Andean-group strains mostly attack large-seeded Andean beans, while Mesoamerican strains attack both groups, which is why varieties from one gene pool can fail when grown in a new area.

Signs in the crop, stage by stage

Crop stage	What you see
Leaves	Grey to brown angular spots limited by veins, often with a yellow halo; dark grey tufts of spores on the undersides; spots merge and leaves yellow and drop.
Pods	Oval to round reddish-brown spots with darker borders; poorly filled pods.
Stems and seed	Elongated brown lesions on stems and branches; shrivelled or discoloured seed.

Disease cycle of angular leaf spot of bean

Life cycle of Angular leaf spot of bean — diagram drawn by Laisha from the stages below. Durations depend on temperature.

The fungus survives on infected crop debris and on seed. In humid weather it produces spores that are spread by wind and rain splash to leaves, where they infect through pores. New spots produce spores within about a week or two, so several cycles occur in a season.

Stage	Duration	Notes
Survival on debris and seed	Between seasons	Debris can carry it for many months.
Infection	During humid periods	Through stomata.
Lesion development and sporulation	About 9-12 days	Tufts on leaf undersides.
Spread	Repeated cycles	Wind and rain splash.

Temperature

Most severe at moderate temperatures of about 16-28 °C with alternating wet and dry periods.

Generations

Several cycles per season.

Conditions that favour it

Moderate temperatures with periods of high humidity, infected debris from previous crops, farm-saved infected seed, continuous bean cropping and susceptible varieties.

Economic threshold level (ETL)

There is no numeric economic threshold; protection relies on clean seed, rotation and resistant varieties, with fungicides started when the first spots appear in susceptible varieties where this is economic.

Thresholds are local. They depend on crop price, control cost, variety and natural-enemy activity, so use the figure your local extension service publishes where one exists.

Damage and yield loss from angular leaf spot of bean

Early defoliation and pod infection reduce yield and seed quality; losses of 40-80% have been reported in susceptible varieties in Africa and Latin America.

Monitoring

Inspect leaves from flowering onward, turning them over to look for dark spore tufts under angular spots.
Check pods for reddish-brown spots and record disease levels to guide variety choice.
Compare plots of different varieties at the same site; large differences in spotting are a quick guide to which varieties resist the local pathogen population.

How to control angular leaf spot of bean (integrated management)

Control works best as a sequence: prevent, monitor, then act only when a threshold or a risk forecast says so, using the least disruptive option that works.

Cultural control

Use clean, certified seed; avoid saving seed from infected crops.
Rotate beans with non-legume crops for at least one or two seasons, and remove or bury crop debris.
Avoid planting new bean crops next to infected older ones.
Intercropping beans with maize, common on small farms, can slow spore spread between bean plants, though the effect varies with spacing and season.
Where seed is saved on the farm, select seed only from healthy plants and pods without spots.

Biological control

Some biological products have been tested with limited and variable results.

Host resistance

Resistance genes (named Phg genes) are available from both Andean and Mesoamerican beans; combining genes from both gene pools gives more durable resistance because pathogen groups specialise on each pool.

Chemical control of angular leaf spot of bean — by mode-of-action group only

Laisha names chemical options only by their resistance-committee mode-of-action group (IRAC for insects, mites and nematodes, FRAC for fungi, oomycetes and bacteria, HRAC for weeds), never by active ingredient or product. What is registered differs by country and changes over time; the label and your local plant-protection authority decide what may be used, on which crop, at what rate and with what pre-harvest interval.

Foliar fungicides applied at the first symptoms and repeated during humid weather reduce losses in susceptible varieties. What is registered differs by country and changes over time; follow the label and your local plant-protection authority.

Scheme	Group	Mode of action	Notes
FRAC	3	Demethylation inhibitors (DMI)	Medium resistance risk.
FRAC	11	Quinone outside inhibitors (QoI)	High resistance risk; use in mixtures.
FRAC	M05	Chloronitriles (multi-site)	Protectant.

Resistance management

Alternate and mix fungicide groups and rely on resistant varieties and clean seed.

Look-alikes and how to tell them apart

Bean anthracnose — Dark reddish to black lesions along the veins on leaf undersides and sunken pod lesions with pink spore masses.
Bean rust — Small raised reddish-brown pustules that release powdery spores.
Common bacterial blight — Water-soaked spots with yellow edges that turn brown and papery, without spore tufts.

Host range

Common bean and other Phaseolus species (such as runner bean); occasionally other legumes in tests.

What is still uncertain

Pathogen diversity is high and changes the effectiveness of single resistance genes.
Loss estimates differ widely between regions and seasons.
How long the fungus survives on buried debris under tropical conditions is not well documented.

Grow guides for its host crops

How to grow the crop well is the first line of defence. Laisha's free grow guides cover each crop from sowing to harvest:

How to grow Common bean How to grow Green bean

Not sure this is what you are seeing?Ask Laisha: describe the symptoms or send a photo, and get a reasoned first read with what to check next — for your crop, your stage and your region.Ask Laisha

Sources

Pseudocercospora griseola (angular bean leaf spot) datasheet — CABI Compendium. https://doi.org/10.1079/cabicompendium.40010
Pseudocercospora griseola (PHAIGR) — EPPO Global Database. https://gd.eppo.int/taxon/PHAIGR
Angular leaf spot: a disease caused by the fungus Phaeoisariopsis griseola on Phaseolus vulgaris — Advances in Applied Microbiology (Elsevier). https://doi.org/10.1016/s0065-2164(03)01009-8
Status and management of angular leaf spot disease of beans caused by Phaeoisariopsis griseola — Indian Phytopathology (Springer). https://doi.org/10.1007/s42360-023-00626-9

Written by Laisha from the sources above, in its own words. This page is general reference, not a prescription: confirm identification locally and follow the label and your plant-protection authority.