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
- 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
- Bullet-shaped beetles
- Slender tan to black
- 1/2-inch long
- "Click" beetles
- Beans, corn, onions and sugar beets
- Potatoes and small grains
- Seed treatments for cereals grown in rotation with beets
- Other crops
Damage and Symptoms
- Reduced seedling stand (early season)
- 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)
- 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.
Minimize initial colonization and establishment
Slow rate of increase once established
- 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.
- 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
- Minimize soil insecticides to conserve natural enemies such as predatory ground beetles and fungal disease.
- Soil core sampling
- Bait stations
- 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
Caution: Read Pesticide Labels
Pesticide labels override other recommendations.