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Agronomy

Bean Leaf Beetle

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  • Latin name is Ceratoma trifurcata
  • Although the larvae feed on soybean roots, most damage occurs from adult feeding on foliage or pods
  • Found east of the Rocky Mountains, wherever soybeans are grown
  • No significant natural enemies are known
  • Hosts: alfalfa, clover, green beans, wild legumes such as tick trefoil
  • Generations per year
    • 3 – Southeast United States
    • 2 – Iowa and Illinois
    • 1 to 2 – Wisconsin
    • 1 – Canada
  • Adults overwinter in woodlots and fence rows
  • Quickly killed if exposed to temps below 14° F
  • Adults may feed on alfalfa in spring before soybeans emerge


bean leaf beetle  bean leaf beetle

Crop Symptoms

  • Impact from larvae is unknown, but thought to be insignificant
  • Leaf feeding from adults causes little impact unless defoliation exceeds 25%
  • Pod feeding results in greatest damage and affects both quality and yield
  • Adults also transmit bean pod mottle virus, which:
    • Reduces soybean yield
    • Reduces soybean quality
    • Causes green stem and delays harvest

Crop Symptom Pictures

Leaf Injury

leaf injury   leaf injury

Area of green stem

area of green stem

Pest ID

Adult:

  • Bean leaf beetle adults are 1/5 inch long
  • Color is typically dark yellow, but may be orange or red
  • Wing covers often with four “rectangular” marks, but may have two or no marks
  • Best identifying mark—black triangle behind pronotum (neck region)

Larvae:

  • Found in soil near roots and resemble corn rootworm larvae
  • Body color is white and head color is dark brown/black
  • Often found feeding in nodule

bean leaf beetle  bean leaf beetle  bean leaf beetle

Management Considerations

Resistance

  • Neither native nor transgenic resistance are currently available for bean leaf beetle

Beneficial Insects (Natural Enemies)

  • Very little impact documented
  • Not a recognized deterrent to beetle populations

Planting

  • If the field has a history of bean leaf beetle injury or bean pod mottle/green stem, consider planting slightly later after most bean leaf beetle adults have moved away from
    the area


Scouting Practices

Early Pod Fill Stages: R1-R3 

  • If defoliation approaches 20 to 25% and large numbers of BLB adults are present, consider insecticide application, especially if beetles exceed 20 per 20 sweeps of a sweep net
  • Decision should be based on increasing or decreasing beetle numbers, costs of control and grain price of soybeans

Late Pod Fill Stages: R5-R7  

  • If pod injury is above 10% and beetles exceed 3 per sweep, consider insecticide application, especially if other pod feeding insects (grasshoppers) are present
    • Value of control will depend on continuing injury and pod maturity

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