Bean rust

Uromyces appendiculatus Uromyces appendiculatus (Pers.) Unger, 1836 · formerly or also: Uromyces phaseoli

roya del frijol · Spanish, Latin America
ferrugem do feijoeiro · Portuguese, Brazil
rouille du haricot · French, France and Africa

Bean rust covers bean leaves with small, raised, reddish-brown pustules that release powdery, rust-coloured spores, usually on the undersides of leaves and often with a yellow halo. Heavily infected leaves dry and drop early, reducing yield, especially when infection begins before flowering. The rust has hundreds of races, so resistant varieties need several resistance genes to stay effective.

Green bean leaves with bean rust: many small yellowish rust spots. Photo: Rasbak, CC BY-SA 3.0, via Wikimedia Commons.

Type: Fungal disease · Fungus (rust fungus, basidiomycete)
Classification: Fungi › Pucciniomycetes › Pucciniales › Pucciniaceae
Main crops: Common bean, Green bean, Lima bean
Found in: Africa, Americas, Asia, Europe and Oceania
Chemical groups: FRAC 11, FRAC 3, FRAC M05 (mode-of-action groups, not products)
Last reviewed: 2026-10-20

What causes bean rust?

Bean rust is caused by Uromyces appendiculatus Uromyces appendiculatus (Pers.) Unger, 1836, a fungus (rust fungus, basidiomycete) (order Pucciniales, family Pucciniaceae).

Older or alternative scientific names: Uromyces phaseoli.

Where it occurs

Found worldwide wherever beans are grown, most damaging in humid tropical and subtropical regions and in irrigated crops with dew.

Region	Status
Africa	Widespread
Americas	Widespread
Asia	Widespread
Europe and Oceania	Present

Symptoms and identification of bean rust

The organism

A rust fungus that completes its whole life cycle on beans. The main spreading spores (urediniospores) are produced in cinnamon-brown pustules; black teliospores form in older pustules late in the season and help it survive between crops in some regions. More than 250 races have been identified. Rust spores are blown long distances by wind, so infections can start even in fields where beans have not been grown recently.

Signs in the crop, stage by stage

Crop stage	What you see
Early infection	Small white or pale yellow raised flecks, mainly on the undersides of leaves.
Pustules	Round, reddish-brown pustules up to about 2 mm across that burst to release powdery rust-coloured spores, often surrounded by a yellow halo; spores rub off on fingers.
Severe infection	Leaves turn yellow, dry and drop; pustules on pods and stems; black pustules (telia) late in the season.

Disease cycle of bean rust

Life cycle of Bean rust — diagram drawn by Laisha from the stages below. Durations depend on temperature.

Urediniospores carried by wind land on leaves and infect when leaves stay wet for many hours. New pustules appear and release spores within about 10-14 days under good conditions, so the disease builds up quickly through repeated cycles. In some regions the fungus survives between crops as teliospores on debris, or carries on in continuous or volunteer bean plantings.

Stage	Duration	Notes
Survival	Between crops	Teliospores on debris, or volunteer beans.
Infection	About 10-18 hours of leaf wetness	Moderate temperatures.
Pustule formation and sporulation	About 10-14 days	Many cycles per season.
Telia formation	Late season	Black resting spores.

Temperature

Favoured by moderate temperatures, below about 30 °C, with long dew periods; hot, dry weather slows it.

Generations

Many cycles per season.

Conditions that favour it

Long periods of leaf wetness from dew, rain or sprinkler irrigation, moderate temperatures, dense canopies, nearby infected bean crops or volunteers, and susceptible varieties. Staggered plantings that keep young bean leaves in the area for months allow the rust to build up from crop to crop.

Economic threshold level (ETL)

There is no numeric economic threshold; fungicides are used preventively or at the first pustules in susceptible varieties where rust is common, especially before flowering.

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 rust

Yield losses of 20-50% or more occur when rust becomes severe before or during flowering; pod infection lowers quality in green beans. In irrigated and dewy environments the rust can build up quickly from a few early pustules, so infection before flowering is the main risk.

Monitoring

Inspect the undersides of leaves weekly from early growth, especially after dewy nights.
Rub suspicious spots to see if powdery rust-coloured spores come off.
Watch neighbouring and volunteer bean plantings, which can be sources of spores.
Record rust severity at flowering, when control decisions matter most for yield.

How to control bean rust (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

Plough in or destroy crop debris and volunteer beans; rotate with non-host crops.
Avoid planting new crops next to older infected ones; plant with spacing that allows leaves to dry.
Avoid sprinkler irrigation in the evening.
Where beans are grown in several seasons a year, leave a break without beans in an area to interrupt the rust cycle.
Destroy volunteer beans growing between seasons, especially near irrigated fields.

Biological control

Some biological products have been tested with limited effect; none replaces resistance and fungicides where rust is severe.

Host resistance

Varieties with combinations of resistance genes (named Ur genes, such as Ur-3, Ur-4, Ur-5 and Ur-11) are the most effective and economical control; because of the many races, single genes are often overcome.

Chemical control of bean rust — 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.

Fungicides protect leaves when applied before or at the first pustules. 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	11	Quinone outside inhibitors (QoI)	High resistance risk; use in mixtures.
FRAC	3	Demethylation inhibitors (DMI)	Curative activity.
FRAC	M05	Chloronitriles (multi-site)	Protectant.

Resistance management

Alternate and mix groups with different modes of action, and use resistant varieties with stacked Ur genes.

Look-alikes and how to tell them apart

Asian soybean rust — Tan or reddish-brown lesions with small volcano-shaped pustules on soybean, not bean.
Angular leaf spot — Flat angular spots between veins with dark spore tufts, not raised powdery pustules.
Common bacterial blight — Water-soaked spots turning brown and papery with yellow edges; no powdery spores.

Host range

Common bean and other Phaseolus species, including runner, lima and tepary beans; cowpea rust is caused by a different species (Uromyces vignae).

What is still uncertain

Race composition varies widely by region and changes over time.
The importance of teliospores for survival differs between climates.
Fungicide timing guidelines were developed mainly for dry and snap beans in temperate regions.

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 Lima 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

Uromyces appendiculatus (bean rust) datasheet — CABI Compendium. https://doi.org/10.1079/cabicompendium.55816
Uromyces appendiculatus (UROMAP) — EPPO Global Database. https://gd.eppo.int/taxon/UROMAP
Dry bean rust — Nebraska Extension CropWatch. https://cropwatch.unl.edu/plantdisease/drybean/rust
Characterization of Uromyces appendiculatus first races in Sri Lanka and identification of genes for resistance — Plant Disease (APS). https://doi.org/10.1094/pdis-08-22-1942-re

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.