moderate severity

Cotton Bacterial Blight (Angular Leaf Spot)Identification & Treatment Guide 2026

Xanthomonas citri pv. malvacearum · Family: Xanthomonadaceae

Cotton bacterial blight (Xanthomonas citri pv. malvacearum) causes angular water-soaked leaf spots, black arm on stems, and boll rot. Yield losses reach 10-35%. The bacterium is seed-borne. Manage with acid-delinted seed, resistant varieties, crop rotation, and copper sprays. Avoid working in wet fields. Remove and burn severely infected plants.

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Quick Diagnosis

moderate

Cotton Bacterial Blight (Angular Leaf Spot)

Affects: leavesstemsbollsbracts
Peak Season: Mid-season during warm (25-35°C) wet weather with windstorms
Spread Risk: Moderate
Spread By: Seed-borne (primary), rain splash, wind-driven rain, contaminated gin trash

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Symptoms: What does Cotton Bacterial Blight (Angular Leaf Spot) look like?

Visual identification guide — tap each stage for details

Angular water-soaked spots on cotton leaf from bacterial blight — Angular water-soaked spots bounded by leaf veins

Dark black arm lesion on cotton stem from bacterial blight — Black arm — dark elongated stem lesion that can girdle branches

Cotton boll rot from bacterial blight with stained lint — Boll rot with stained degraded lint — reduced quality and yield

Early Stage

Small angular water-soaked spots on leaves
Small (2-5 mm) angular, dark green, water-soaked spots appear on lower leaves, bounded by veins. Spots look translucent when held to light.

Mid Stage

Angular brown leaf lesions and black arm
Spots enlarge, dry to brown, and may coalesce. Stem infection produces long, dark (black) lesions on branches and main stem — the 'black arm' phase. Girdling can cause branch or plant death.

Late Stage

Boll rot and lint staining
Boll infection through bracts causes internal rot. Lint becomes stained and degraded. Bolls may fail to open properly or shed prematurely. Severely infected fields show 10-35% yield loss.

Causes: Why is my plant getting Cotton Bacterial Blight (Angular Leaf Spot)?

Environmental triggers and disease cycle

Planting infected seed (primary inoculum)
Warm rain and windstorms spreading bacteria
Hail or wind damage creating wounds for bacterial entry
Continuous cotton cropping
Gin trash (contaminated ginning residues) in field

Disease Lifecycle

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Host Plant

Susceptible crop

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Pathogen

Xanthomonas

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Conditions

Mid-season during warm (25-35°C) wet weather with windstorms

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Infection

Penetrates tissue

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Symptoms

Visible signs

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Spread

Seed-borne (primary)

Often confused with: Cotton Leaf Curl Disease. See our comparison guide.

How to Treat Cotton Bacterial Blight (Angular Leaf Spot)

Tick each step as you complete it — works offline too

🌿 OrganicSafe for all farms

Organic Treatment Steps

4 steps

Plant resistant varieties — the most practical management for smallholder cotton farmers.
Use acid-delinted seed or hot water treated seed (56°C for 10 minutes) to eliminate seed-borne bacteria.
Remove and burn severely infected plants (showing black arm) to reduce field inoculum.
Rotate with non-malvaceous crops (cereals, legumes) for 2 years minimum.

🧪 ChemicalUse protective equipment

Chemical Treatment Steps

3 steps

Apply copper hydroxide (Kocide 2000) at 2 g/L every 10-14 days during wet weather after disease detection.
Streptomycin sulfate at 100 ppm combined with copper provides better control than copper alone in heavy disease.
Seed treatment with carboxin + thiram (Vitavax Power) provides partial seed disinfection and seedling protection.

Prevention & Seasonal Calendar

Year-round protection plan for your crops

Pre-Planting

Plant resistant varieties from national cotton breeding programs
Use certified, acid-delinted or treated seed

Mid-Season

Rotate cotton with non-host crops for at least 2 years
Plow in cotton stubble and gin trash after harvest

Post-Harvest

Avoid working in fields when foliage is wet
Report unusual or severe outbreaks to cotton extension services

🛡️ Resistant Varieties

Varies by region and raceMany modern varieties carry multiple R genesConsult national cotton research program for current ratings

View full seasonal calendar for your region →

Frequently Asked Questions

Common questions about Cotton Bacterial Blight (Angular Leaf Spot)

What is the 'black arm' symptom?

Black arm refers to dark, elongated bacterial lesions on cotton stems and branches. When bacteria spread from leaf spots into the vascular tissue of the stem, they cause black necrotic streaks that can girdle branches, causing them to wilt and die. The affected stem tissue turns dark brown to black, hence 'black arm.' It is the most destructive phase of the disease.

Does acid delinting kill the bacteria on seed?

Yes. Concentrated sulfuric acid delinting removes the lint (fuzz) from cottonseed and simultaneously kills bacteria on the seed surface. It is the most effective seed treatment for bacterial blight elimination and is standard practice in commercial cotton seed processing. Small-scale farmers without access to acid delinting can use hot water treatment instead.

Can bacterial blight survive in the soil?

The bacterium survives primarily in and on seed and in cotton crop debris (stalks, leaves, bracts). It does not persist long in bare soil without plant material. Plowing in crop debris accelerates decomposition and reduces carryover. The 2-year rotation recommendation is primarily to ensure complete debris decomposition.

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Related Disease

Cotton Leaf Curl Disease

Cotton leaf curl virus (CLCuV complex)

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Affected Plant

Cotton

Gossypium hirsutum / G. barbadense

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Treatment Guide

Full Treatment Protocol

Detailed spray schedule & dosage guide

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