Do I have a wireworm – true or false?

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Wire­worm adults and lar­vae are rel­a­tive­ly com­mon soil pests, attack­ing all field crops. Adults feed on ger­mi­nat­ing shoots, and lar­vae feed on ger­mi­nat­ing seed, seedling roots and shoots caus­ing poor plant vigour or death. Wire­worms are most com­mon in zero till, areas with high stub­ble, or weedy fal­lows. These are habi­tats and food sources that sus­tain the bee­tles and enable them to breed suc­cess­ful­ly.

Crops most at risk are gen­er­al­ly late-plant­ed win­ter crops or ear­ly-plant­ed sum­mer crops, and in par­tic­u­lar spring sorghum because the one year life­cy­cle means that lar­vae have reached their most vora­cious and dam­ag­ing final lar­val stage by September–November.

 falsewireworm-pterohelaus

East­ern false wire­worm (Ptero­he­laeus spp) lar­vae are up to 30 mm long with a scle­ro­tised body and small head.

falsewireworm-gonocephalum

Small false wire­worm or south­ern false wire­worm (Gono­cephalum spp.) lar­vae are sim­i­lar to east­ern false wire­worm, but only grow up to 20 mm long.

 truewireworm

True wire­worm or click bee­tle (Agryp­nus spp.) lar­vae are up to 35mm long, soft bod­ied with a large slant­ed head. The true wire­worm can be a preda­tor of heli­cov­er­pa pupae.

Lifecycle-false_wireworm

Dia­gram of false wire­worm life­cy­cle show­ing crit­i­cal mon­i­tor­ing peri­ods and opti­mal con­trol win­dows

Monitoring

Adults may be present from Decem­ber to May; the crit­i­cal mon­i­tor­ing peri­od is Decem­ber to Feb­ru­ary.

Mon­i­tor for lar­vae pre-plant. Allow suf­fi­cient time to organ­ise seed dress­ings or in-fur­row sprays if required. There are two pri­ma­ry detec­tion meth­ods:

  1. Grain seed bait­ing (where baits of soaked untreat­ed seed are shal­low­ly buried through­out the pad­dock (at about 20 baits/100 ha). Dig up the baits a day after seedling emer­gence.
  2. Scrap­ing the soil sur­face away care­ful­ly with a hand trow­el. Look in pad­docks with plant residue that have had recent rain where a sur­face crust has formed. Lar­vae can often be found at the wet-dry soil inter­face.

Suggested thresholds

Baits (DAF):

  • Sum­mer: An aver­age of one or more wire­worms per bait
  • Win­ter: two or more wire­worms per bait

Hand trow­el (cesar): 10 larvae/m2

Control

Treat­ment for lar­vae needs to occur before the crop is sown. Refer to the APVMA web­site for prod­ucts (includ­ing cur­rent per­mits) reg­is­tered for the lar­vae. A wide range of seed can now be bought pre-treat­ed with insec­ti­cide for soil insect pests.

Sprays and seed dress­ings for lar­val con­trol are not effec­tive against the adults. The opti­mal peri­od for broad­cast­ing treat­ed cracked grain baits for bee­tle man­age­ment is Decem­ber to Feb­ru­ary.

Avoid repeat­ed­ly using just a sin­gle chem­i­cal group as Agryp­nus species had devel­oped resis­tance to sev­er­al organochlo­rine com­pounds (which were wide­ly used as seed and soil treat­ments before being banned in most coun­tries).

Using press wheels at plant­i­ng can assist in min­imis­ing insect dam­age by:

  • injur­ing large insects,
  • restrict­ing the move­ment of lar­vae through the soil, and
  • min­imis­ing soil mois­ture loss­es, enabling the seedlings to ger­mi­nate more rapid­ly.

More information

DAF web­site:

Cesar:

Further reading

  • Bai­ley, PT (ed) (2007) Pests of field crops and pas­tures – iden­ti­fi­ca­tion and con­trol. CSIRO Pub­lish­ing
  • Gun­ning, R. V. and For­rester, N. W. (1984), Cyclo­di­ene lin­dane resis­tance in Agryp­nus vari­abilis (Can­déze) (Coleoptera: Ela­teri­dae) in north­ern New South Wales. Aus­tralian Jour­nal of Ento­mol­o­gy, 23: 247–248.
  • Rad­ford, BJ and All­sopp, PG (1987) Use of insec­ti­cides and a press wheel to con­trol soil insects affect­ing sorghum and sun­flower estab­lish­ment in south­ern Queens­land. Jour­nal of the Aus­tralian Ento­mo­log­i­cal Soci­ety. 26 (2): 161–167
  • Syn­gen­ta wire­worm field guide (Cana­da) [300KB pdf file]