Agriculture & Natural Resources

IPM- Processing Lima Bean Scouting Guidelines

I. Pre-planting Decisions

  • Select varieties with disease resistance for downy mildew.
  • Rotate fields with non-legume crops and plow under crop residue to avoid root rot.

II. Emergence to Third Trifoliate

A. Spider Mites:

  • Sampling: Field should be scouted on a weekly basis from early July through early August, especially during hot, dry seasons. Begin sampling along field borders and look for signs of white stippling near the base of leaves. Examine 10 leaves in 5 to 10 locations throughout a field and count the number of mites per leaf.
  • Thresholds: Treatment is recommended when white stippling is first noticed and you find 20 mites per leaflet. Rainfall and high humidity can help to reduce mite development and survival. However, rain will not provide enough suppression when heavy populations are developing under high temperatures.

B. Mexican Bean Beetle and Bean Leaf Beetle

  • Sampling: Begin sampling fields at plant emergence especially along field margins next to overwintering sites. Record the percent of stand reduction, estimate the percent defoliation and count the number of beetles per plant.
  • Thresholds: (a) Before the First Trifoliate: 6 or more beetle per row foot and 75% stand reduction (b) First to Third Trifoliate: 2 or more beetles per plant and 20% defoliation

III. Prebloom Stage: Third Trifoliate to Pre-Bud

A. Potato Leafhopper

  • Sampling: Using a standard 15-inch diameter sweep net, take 10 sweeps in 10 locations throughout a field. Count the number of leafhopper adults and nymphs and calculate the number of leafhoppers per sweep.
  • Thresholds: Treatment should be applied if populations exceed 5 or more per sweep.

B. Mexican Bean Beetle

  • Sampling: At this stage, counting the number of beetles per plant is too time consuming. Instead, estimate the percent defoliation to the nearest10% on 5 plants in 5 to 10 locations throughout a field. It is also important to determine the predominant life stage present (eggs, adults, larvae or pupae).
  • Thresholds: A treatment should be applied if defoliation exceeds 20%. Controls should be delayed if the predominant life stages are eggs and/or pupae.

C. Bean Aphid

  • Sampling: Aphids are generally found on the lower leaf surfaces and terminal buds. Sample 5 terminals in 5-10 locations throughout a field and count the number of terminals infested with 5 or more aphids.
  • Thresholds: Treatment is recommended when populations are found throughout a field and 50% or more of the terminals have 5 or more aphids per terminal.

D. Green Cloverworm

  • Sampling: Using a standard 15-inch sweep net, take 10 sweeps in 10 locations throughout a field and count the number of larvae per sweep.
  • Thresholds: Apply an insecticide treatment if defoliation exceeds 20% and the cloverworm numbers exceed 15 larvae per sweep.

IV. Bud Stage through Harvest

A. Stinkbugs and Lygus Bug

  • Sampling: Sampling should begin at the bud stage and continue on a weekly basis until 5 days from harvest. Using a standard 15-inch sweep net , take 10 sweeps in 10 locations throughout a field. Sampling should be done early in the morning or late afternoon when insects are most active.
  • Thresholds: Treatment should be applied if the adult and/or nymphal count exceeds 15 per 50 sweeps.

B. Corn Earworm

  • Sampling: Monitoring should begin at full bloom and continue on a twice a week basis until harvest. Using a 3 foot drop cloth placed between two rows and shaking the plants over the cloth, sample a minimum of 10 locations throughout a field. Each shake sample covers 6 foot of row. Count the number of larvae and estimate the average larval size.
  • Thresholds: When possible, treatment should be delayed until at least 1/3 of the larval population has reached ½-inch in size. Treatment should be applied when you find one or more larvae per 6 foot of row.

 

University of Delaware IPM Program
Joanne Whalen – Extension IPM Specialist