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Wireworms

Order: Coleoptera
Family: Elateridae
Species: 100 species of wireworms in Idaho, 2 commonly infest field crops

  • Sugar beet wireworm (Limonius californicus)

  • Pacific Coast wireworm (Limonius canus)

    • Both native to wet soils along streams

    • Neither survives dryland cropping conditions

wireworm
Wireworm

Pests as larvae

Appearance

Larvae

  • Hard-bodied, slender, cylindrical
  • Shiny yellow-to-brown "worms"
  • 3/4 to 1-inch long when mature
  • Three pairs small legs behind head
  • Last body segment notched (skeleton key-hole)
Potential larval look-alikes
  • Ground beetle larvae
    • Beneficial predators of many soil-borne insects
    • Variable color (yellow, brown, black)
    • No key-hole notch
    • Crawl rapidly when disturbed

Adults

  • Bullet-shaped beetles
  • Slender tan to black
  • 1/2-inch long
  • "Click" beetles

Host plants

Moderately favorable

  • Beans, corn, onions and sugar beets

Infestations likely

  • Potatoes and small grains
  • Seed treatments for cereals grown in rotation with beets

Relatively unfavorable

  • Other crops

Damage and Symptoms

Above ground

  • Reduced seedling stand (early season)

Below ground

  • Feed on hair roots and taproot
  • Seed destruction and girdled seedlings
  • Root-surface scarring and channels
  • Winding tunnels into taproot
  • Secondary root growth ("forked" bulbs and tubers)

Biology

  • Life cycle
    • Complete metamorphosis egg > larvae > pupa > adult.
    • 3-4 years for egg to adult development with virtually all the time spent as larvae in the soil.
    • The egg and pupal stages each last ~1 month.
    • Larvae feed in the soil for 3-4 growing seasons.
    • Adults live ~ 9 months primarily hibernating in the soil.
  • Fall/winter: Larvae and adults reside in top 9 to 24-inches of soil.
  • Spring: Adults move to the surface when soil is 50-55 degrees F. Mated females burrow back into the soil where they lay 350 eggs over 3 weeks. Then they fly to other parts of the field and lay more eggs, causing spotty infestations such that some fields have severe damage and others escape damage.
  • Summer: Larvae of all stages are present feeding in the soil at the same time, usually in the top 6-inches unless the soil is too dry or hot (>80 F). Pupae develop in the late summer within an earthen cell and remain in the soil until the next spring.

Control Strategy

  • Minimize initial colonization and establishment

  • Slow rate of increase once established

Control Options

Predict Infestations

  • Wireworm damage in any 4 or 5 prior crops
    • Extended potential damage due to 3-4 year life cycle
  • Wheat and barley grown up to 4 years before
    • These are excellent hosts that are often not treated for wireworms because of the low profit margin.
  • Fields with grassy weeds in previous year
    • These are attractive ovipositional plants and serve as larval host plants.
  • Fields taken out of pastures and grassy sods
    • These are attractive ovipositional plants and serve as larval host plants. There is potentially a heavy build-up due to long term use.

Cultural

  • Rotate with a non-host such as alfalfa
    • Creates dry, compact soil unfavorable to wireworms
    • Do not allow alfalfa to become weedy with grasses
    • At least 3 years of alfalfa, beets, potatoes or onions row crop

Biocontrol

  • Minimize soil insecticides to conserve natural enemies such as predatory ground beetles and fungal disease.

Scouting

  • Soil core sampling
  • Bait stations

Pesticides

Contact Us

Integrated Pest Management

Mailing Address:
University of Idaho, Boise Center
322 E Front St, Suite 180
Boise, ID 83702

Phone: 208-364-4046

Fax: 208-364-4035

Email: rhirnyck@uidaho.edu