University of Idaho Pest Management Center

*Wireworms*
*species:*	100 spp wireworms in Idaho 2 commonly infest field crops Sugarbeet wireworm Limonius californicus Pacific Coast wireworm Limonius canus - both native to wet soils along streams - neither survives dryland cropping conditions ORDER: Coleoptera (beetles) FAMILY: Elateridae (click beetles)
*identification:*
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) potentially confusing larval look-alikes ground beetle larvae - beneficial predators of many soil-borne insects - variable color (yellow to brown to black) - no key-hole notch - crawl rapidly when disturbed
*adult*	- bullet-shaped beetles - slender tan to black - 1/2-inch long - “click” beetles
damage and symptoms:	adults harmless larvae chewing mouthparts feed on beet seed, hair roots & taproot above ground symptoms reduced seedling stand (early season) below ground symptoms seed destruction & girdled seedlings root-surface scarring & channels winding tunnels into taproot secondary root growth (“forked” beets)
biology:	complete metamorphosis four life stages egg > larvae > pupa > adult 3 to 4 years for egg to adult development virtually all time spent as larvae in soil egg and pupal stages each last 1 month adults live about 9 months primarily hibernating in soil only life stage that occurs above ground larvae of all ages present in soil at same time fall/winter - larvae and adults 9 to 24-inches in soil spring - adults move to surface when 50-55 F soil - mated females burrow back into soil - lay 350 eggs over 3-wk - fly to other parts of the field & lay more eggs spotty infestations fields w/severe damage vs escape damage Lifecycle spring Pacific Coast wireworm - eggs in bare soil sugarbeet wireworm - eggs in soils shaded by vegetation grassy swales, rock piles, ditchbanks eggs hatch within 1 month summer (years 1- 4) - larvae feed for 3 or 4 growing seasons usually w/in 6-inches of soil surface unless soil too dry or too hot (>80 F) late summer (years 3 or 4) - pupae w/in earthen cell - develop to adults w/in 3 or 4 weeks remain in the soil until next spring
CONTROL OPTIONS
*understanding wireworm infestations:*	predictor #1: wireworm damage in any 4 or 5 prior crops — extended potential damage due to 3-4 yr life cycle predictor #2: wheat and barley up to 4 years before sugarbeets — excellent hosts — often not treated w/insecticide for wireworms low profit margin vs high-value sugarbeets & potatoes predictor #3: fields with grassy weeds year before beets — attractive ovipositional site — larval host plants predictor #4: fields taken out of pastures and grassy sods — attractive ovipositional site — larval host plants long-term, potentially heavy build-up
*strategy:*	minimize initial colonization & establishment slow rate of increase once established
cultural:	rotate w/non-host alfalfa creates dry, compact soil unfavorable to wireworms 3+ yrs alfalfa beets (potatoes/onions) row crop do not allow alfalfa to become weedy with grasses - moderately favorable hosts beans / corn / onions / sugarbeets - infestations likely small grains: potato seed treatments for cereals grown in rotation w/beets - relatively unfavorable other crops
biocontrol:	- conserve natural enemies via minimize soil insecticide predatory ground beetles & fungus disease - no cost-effective commercial products or agents (yet)
*scouting & thresholds:*	- soil core sampling vs bait stations determine pre-plant presence: absence (1) dig 1/4 -ft2 cores to 12-inches spring pre-plant (2) recover larvae via screening through sieves (3) one core per each 1-acre field size, randomly spread-out across field draw larvae to lures in soil (1) bury fist-size portion of bait 4 to 6 inches deep - whole wheat & corn / chopped carrots / potatoes / oatmeal or wheat flour - CO2 from fermenting baits attracts wireworms (2) bait before planting either during prior fall or spring - need moist soils + 45 degrees F at 6-inches else wireworms inactive (3) 1 bait per each 1-acre field size - randomly spread-out across field (4) examine (screen) baits + soil in 5 to 10 days - NO thresholds - NO postemergence rescue treatments pre-plant or at-plant ONLY
conventional insecticides:	chlorpyrifos (Lorsban 15G, Nufos 15G) – 1.5 to 2 lb ai/acre at planting (suppression only) diazinon (14G, 5 Bait, AG500, AG600 WBC, 50WP, 4E) – 3 to 4 lb ai/acre terbufos (Counter 20CR) – 0.6 to 1.2 oz ai/1000 row ft banded or modified in-furrow at planting IF low wireworm density THEN band at planting IF high wireworm density THEN broadcast before planting

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