high severity

Bean Angular Leaf SpotIdentification & Treatment Guide 2026

Pseudocercospora griseola · Family: Mycosphaerellaceae

Bean angular leaf spot (Pseudocercospora griseola) causes angular brown lesions bounded by leaf veins, reducing yield 50-80% in common bean across Africa and Latin America. The fungus is seed-borne. Manage with resistant varieties, certified disease-free seed, crop rotation (2+ years), and fungicide sprays (mancozeb + carbendazim) starting at first flower.

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Quick Diagnosis

high

Bean Angular Leaf Spot

Affects: leavespodsstems
Peak Season: Rainy season; warm (20-25°C) wet conditions with intermittent rain
Spread Risk: Moderate
Spread By: Seed-borne (primary inoculum source), rain splash of conidia, wind-driven rain, infested crop debris

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Symptoms: What does Bean Angular Leaf Spot look like?

Visual identification guide — tap each stage for details

Small dark spots on bean lower leaves from early angular leaf spot — Initial small dark spots on lower leaves

Characteristic angular brown lesions bounded by veins on bean leaf — Diagnostic angular lesions bounded by leaf veins

Circular reddish-brown sunken lesions on bean pods from ALS — Pod lesions with dark centers — seed infection develops from these

初期段階

Small dark brown spots on lower leaves
Small dark spots appear on primary leaves and lower trifoliate leaves. Spots are initially circular but soon become angular.

中期段階

Angular brown lesions bounded by leaf veins
Characteristic angular (geometric) brown lesions bounded by major and minor leaf veins. Lesions are dark brown on the upper surface and may have gray sporulation on the lower surface. This angular shape is the diagnostic hallmark.

後期段階

Severe defoliation and pod spotting
Extensive defoliation occurs from coalescent lesions. Pods develop circular reddish-brown sunken lesions with dark centers. Seed-borne inoculum develops in infected pods, perpetuating the disease cycle.

Causes: Why is my plant getting Bean Angular Leaf Spot?

Environmental triggers and disease cycle

Planting infected seed (primary inoculum source)
Infested crop debris from previous bean crops
Warm humid weather with intermittent rain during flowering
Susceptible varieties
Continuous bean cropping without rotation

Disease Lifecycle

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Host Plant

Susceptible crop

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Pathogen

Pseudocercospora

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Conditions

Rainy season; warm (20-25°C) wet conditions with intermittent rain

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Infection

Penetrates tissue

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Symptoms

Visible signs

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Spread

Seed-borne (primary inoculum source)

Often confused with: Bean Common Mosaic Virus Disease. See our comparison guide.

How to Treat Bean Angular Leaf Spot

Tick each step as you complete it — works offline too

🌿 OrganicSafe for all farms

Organic Treatment Steps

4 steps

Plant certified disease-free seed — this is the most critical intervention to break the seed-borne infection cycle.
Plant resistant varieties carrying Phg resistance genes appropriate for local pathogen populations.
Rotate beans with non-host crops (cereals, root crops) for at least 2 seasons.
Remove and destroy crop residues after harvest to reduce field inoculum.

🧪 ChemicalUse protective equipment

Chemical Treatment Steps

4 steps

Apply mancozeb (Dithane M-45) at 2.5 g/L starting at first flower (R6) and repeat every 10-14 days during wet weather.
Alternate with carbendazim (Bavistin) at 1 g/L for systemic protection.
Apply azoxystrobin (Amistar) at 1 ml/L for long-lasting protection during pod fill.
Treat seed with thiram (3 g/kg) or carbendazim (2 g/kg) before planting to reduce seed-borne inoculum.

Prevention & Seasonal Calendar

Year-round protection plan for your crops

Pre-Planting

Use certified disease-free seed from reputable sources
Plant resistant varieties — multiple Phg genes provide broad resistance

Mid-Season

Rotate with non-host crops for at least 2 years
Remove or incorporate bean residues after harvest

Post-Harvest

Avoid planting during the wettest months if possible
Maintain adequate but not excessive plant spacing for air circulation

🛡️ Resistant Varieties

CAL 143 (Andean)Mexico 54 (Phg-2)AND 277 (partial resistance)KAT B1 (Kenya)

🌼 Companion Planting

These plants can reduce Bean Angular Leaf Spot pressure when grown nearby:

maize

View full seasonal calendar for your region →

Frequently Asked Questions

Common questions about Bean Angular Leaf Spot

Why are two pathogen gene pools important for farmers?

P. griseola has Andean and Mesoamerican lineages with different virulence patterns. A variety resistant to Andean strains (common in East Africa) may be completely susceptible to Mesoamerican strains (common in Central America). This means resistance must be tailored to local pathogen populations — a variety that works in Kenya may fail in Honduras.

Can I save seed from angular leaf spot-infected fields?

This is not recommended because the pathogen is seed-borne and can survive on/in seeds for over 2 years. Planting infected seed is the primary way the disease is introduced to new fields. Always source certified disease-free seed, especially for the first planting in a clean field.

How does angular leaf spot affect nutrition and food security?

Common bean is the primary protein source for over 200 million people in Africa. Angular leaf spot reduces both yield (50-80%) and grain quality. In East Africa, bean losses from ALS directly translate to protein deficiency, making this disease a significant food security concern. Resistant varieties are considered a high-priority intervention by CIAT and national bean programs.

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Related Disease

Bean Common Mosaic Virus Disease

Bean common mosaic virus (BCMV)

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Affected Plant

Common Bean

Phaseolus vulgaris

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Treatment Guide

Full Treatment Protocol

Detailed spray schedule & dosage guide

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