Bean common mosaic and bean common mosaic necrosis

Bean common mosaic virus and Bean common mosaic necrosis virus ICTV species: Potyvirus phaseovulgaris (BCMV) and Potyvirus phaseoli (BCMNV) · formerly or also: BCMV, BCMNV (formerly the NL-3, NL-5 and NL-8 strains of BCMV)

mosaico común del frijol · Spanish, Latin America
mosaico-comum do feijoeiro · Portuguese, Brazil
mosaïque commune du haricot · French, France and Africa
black root · English, Worldwide (necrotic form)

Bean common mosaic and its close relative bean common mosaic necrosis are virus diseases that mottle bean leaves light and dark green, make them curl and pucker, and stunt plants. Both viruses are carried in seed and spread by aphids. In bean varieties that carry the resistance gene called I, the necrosis virus can kill plants by causing 'black root', a blackening of the vascular system. Clean seed and resistant varieties are the main defence.

Bean leaves with bean common mosaic: light and dark green mottling. Photo: Howard F. Schwartz, Colorado State University, Bugwood.org, CC BY 3.0, via Wikimedia Commons.

Type: Virus disease · Virus (potyviruses with RNA genomes), spread by seed and aphids
Classification: Patatavirales › Potyviridae › Potyvirus
Main crops: Common bean, Green bean, Cowpea
Found in: Africa, Americas, Europe and Asia, Oceania
Last reviewed: 2026-10-20

What causes bean common mosaic and bean common mosaic necrosis?

Bean common mosaic and bean common mosaic necrosis is caused by Bean common mosaic virus and Bean common mosaic necrosis virus, a virus (potyviruses with RNA genomes), spread by seed and aphids (order Patatavirales, family Potyviridae).

Older or alternative scientific names: BCMV, BCMNV (formerly the NL-3, NL-5 and NL-8 strains of BCMV).

Where it occurs

BCMV is found wherever beans are grown, carried around the world in seed. BCMNV is thought to have originated in Africa and is most common there, but also occurs in Europe, Asia and the Americas.

Region	Status
Africa	Both viruses widespread; BCMNV common
Americas	BCMV widespread; BCMNV present
Europe and Asia	Both present
Oceania	BCMV present

Symptoms and identification of bean common mosaic and bean common mosaic necrosis

The organism

Flexuous, rod-shaped RNA viruses detected by ELISA or RT-PCR. Both are seed-transmitted in common bean, at rates that can be high in susceptible varieties, and spread between plants by many aphid species in a non-persistent way within seconds of probing.

Signs in the crop, stage by stage

Crop stage	What you see
Plants from infected seed	Mosaic of light and dark green on the first true leaves; leaves narrow, curled downward and puckered; plants stunted.
Plants infected by aphids	Mosaic and leaf distortion on new growth; fewer pods, often deformed.
Black root (varieties with the I gene)	Wilting and death of the growing tip, brown to black discoloration of the vascular tissue in stems and roots, and rapid death of the plant, especially with BCMNV or at high temperatures.

Disease cycle of bean common mosaic and bean common mosaic necrosis

Life cycle of Bean common mosaic and bean common mosaic necrosis — diagram drawn by Laisha from the stages below. Durations depend on temperature.

Infected seed gives rise to infected seedlings scattered through the field. Aphids probing these plants pick up the virus within seconds and spread it to nearby plants during their flights. Infection of plants before flowering can lead to infected seed, carrying the viruses into the next crop and across regions.

Stage	Duration	Notes
Infected seed	Between seasons	Main source and long-distance spread.
Aphid spread	Seconds to minutes	Non-persistent.
Symptom development	About 1-3 weeks	Mosaic or black root.
Seed infection	When infected before flowering	Carries virus forward.

Temperature

Symptoms vary with temperature; black root in plants with the I gene is more likely at high temperatures with some strains.

Generations

Spread continues during aphid activity; carry-over through seed.

Conditions that favour it

Planting farm-saved or uncertified seed, susceptible varieties, high aphid numbers, and nearby infected bean crops or legume weeds.

Economic threshold level (ETL)

There is no economic threshold; seed certification schemes set tolerances for seed-borne virus, and field management is preventive.

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 bean common mosaic and bean common mosaic necrosis

Yield losses range from small to more than half of the crop, and are highest when plants grow from infected seed; black root can kill whole patches of plants. Infected seed lots lose value. Losses are lower when plants are infected late, after flowering, but such plants can still produce infected seed.

Monitoring

Inspect young plants for mosaic and leaf distortion, especially plants scattered through the field from infected seed.
Remove and test suspect plants in seed crops.
Watch for wilting and blackened stems in varieties carrying the I gene.
In seed production, test seed lots in the laboratory before sale or sowing, since infected seeds look normal.

How to control bean common mosaic and bean common mosaic necrosis (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

Plant certified, virus-tested seed and avoid saving seed from infected crops.
Rogue infected plants early in seed crops; avoid planting next to older infected bean crops.
Control legume weeds that may carry the viruses.
Plant early so that crops are past their most sensitive stage before aphid numbers peak.

Biological control

Natural enemies of aphids reduce colonies but cannot prevent non-persistent virus transmission by passing aphids.

Host resistance

Combining the dominant I gene with recessive resistance genes (such as bc-3 or bc-2 with bc-u) protects against both viruses and prevents black root; many improved varieties carry such combinations.

Chemical control of bean common mosaic and bean common mosaic necrosis — 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.

No chemical controls the viruses, and insecticides do not stop non-persistent aphid transmission. What is registered differs by country and changes over time; follow the label and your local plant-protection authority.

Resistance management

Not applicable to chemicals; rely on clean seed and stacked resistance genes.

Look-alikes and how to tell them apart

Bean golden mosaic and other whitefly-transmitted viruses — Bright yellow mosaic with whiteflies present, rather than a green mosaic with aphids.
Mungbean yellow mosaic — Bright yellow patches in mung bean, black gram and other Vigna crops, spread by whiteflies.
Herbicide injury — Leaf distortion appearing at once across rows after spraying, without a mosaic.

Host range

Common bean and other Phaseolus species; some strains of BCMV (including the former blackeye cowpea mosaic virus) infect cowpea and other legumes.

What is still uncertain

Strain composition differs between regions, so the protection given by particular gene combinations can vary.
Seed transmission rates vary with variety and time of infection.

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 How to grow Cowpea

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

Potyvirus bean common mosaic virus datasheet — CABI Compendium. https://doi.org/10.1079/cabicompendium.122024
Potyvirus phaseoli (BCMNV0) — EPPO Global Database. https://gd.eppo.int/taxon/BCMNV0
Bean common mosaic virus and bean common mosaic necrosis virus: relationships, biology, and prospects for control — Advances in Virus Research (Elsevier). https://doi.org/10.1016/bs.aivir.2015.04.002
Bean common mosaic: Dry Beans Pest Management Guidelines — UC IPM. https://ipm.ucanr.edu/agriculture/dry-beans/bean-common-mosaic/
Potyvirus phaseovulgaris (BCMV00) — EPPO Global Database. https://gd.eppo.int/taxon/BCMV00

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.