How to Manage Pests

UC Pest Management Guidelines

Dry Beans

Bean Yellow Mosaic

Pathogen: Bean yellow mosaic potyvirus (BYMV)

(Reviewed 8/07, updated 8/07)

In this Guideline:


The diagnostic symptom of bean yellow mosaic is the bright yellow to green mosaic or mottle appearance of infected leaves, which becomes most apparent on leaves as they become older. Infected leaves also show varying degrees of leaf distortion, down cupping, and wrinkling. Plants infected at a young age may show stunted growth. The striking yellow mosaic symptoms differentiate bean yellow mosaic infections from those of bean common mosaic, which causes light and dark green mosaic patterns of infected leaves.


Bean yellow mosaic has a wide host range in legumes and can readily overwinter in perennial legume crops (e.g., alfalfa, clovers) or weeds (vetch). It also commonly infects gladiolus. The virus is transmitted by over 20 species of aphids (e.g., the pea, green peach, and black bean aphids). Beans become infected when virus-carrying aphids move into bean fields. Transmission of the virus occurs within seconds once aphids begin feeding on the crop. Aphids can efficiently spread the virus within a field, resulting in high rates of infection. The virus is not known to be seed-transmitted in beans.

Bean yellow mosaic virus is in the same virus family as Bean common mosaic virus and commonly occurs in mixed infections with Bean common mosaic virus in field-infected plants. This can confuse diagnosis in the field, which can be particularly important in seed production fields. Antibody tests are often needed for the precise identification of these two viruses.


Locate bean fields as far away from perennial legumes (alfalfa, clover, vetch) and gladiolus fields as possible. The best management approach is to plant resistant varieties. A number of Bean yellow mosaic virus-resistant dry bean varieties are available, whereas few snap bean varieties are resistant. Insecticide sprays to reduce the rate of spread of the virus by aphids are generally not effective, but may provide limited control if applied to nearby fields of forage legumes or to bean fields early in the season.


[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Dry Beans
UC ANR Publication 3446


R. M. Davis, Plant Pathology, UC Davis
C. A. Frate, UC Cooperative Extension, Tulare County

Acknowledgment for contributions to Abiotic Disorders:
A. E. Hall, Botany and Plant Sciences, UC Riverside
Acknowledgment for contributions to Diseases/Abiotic Disorders:
S. R. Temple, Plant Sciences, UC Davis
Acknowledgment for contributions to Diseases (viruses):
R. L. Gilbertson, Plant Pathology, UC Davis

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