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

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

• Check the Database of Pesticides Registered in Idaho (Kelly Database) for pesticides registered in Idaho
• For low wireworm density: Band at planting
• For high wireworm density: Broadcast before planting