False wire worms in seedling crops of canola, sorghum and sunflower

False wire worms (FWW)

  • Grey false wireworm (Isopteron puctatissimus)
  • Bronze field beetle (Adelium brevicorne)
  • Gonocephalum sp
  • Pterohelaeus sp
Objectives Pre sowing Seedling
Insects and damagefalse wireworm larva Where to find them

  • Detection prior to sowing is important as there are no effective post-sowing treatments.
  • Fields with a history of FWW infestation, or in a region where FWW are common are most at risk. Canola is particularly vulnerable to seedling loss.
  • Soil sampling, or the use of germinating grain baits are used to determine the presence and abundance of FWW larvae prior to sowing.

It is possible to inspect a paddock into which canola will be planted the following autumn in spring (September) when fully grown larvae are most visible. Use the same technique for sampling soil for larvae immediately prior to sowing.

Damage

  • Larvae chew seedling roots and shoots
  • Adults chew seedlings at or below ground level, ringbarking seedlings or cutting stems
  • Affected crops may be thinned
  • In heavy infestations, crops may be so badly damaged that re-sowing is necessary.

Damage is more severe when germination and establishment of newly sown crops is impaired by cold and wet, or dry conditions.

Monitoring Count the number of larvae in a quadrat (30x30cm) of soil to 2 cm depth (deeper if soil moisture is deeper). Repeat at 5-10 sites in the field.

Germinating seed baits can be used to monitor for the presence of false wireworm. See monitoring for soil insects for more detailed information.

Inspect areas of poor establishment for characteristic damage to seedlings. Look for signs of damage above ground, and for beetles sheltering in the soil and under stubble.

Occasionally adult beetles (Gonocephalum and Pterohelaeus) can move across emerging crops grazing on cotyledons and terminals.

Natural enemies Carabid beetle larvae feed on soil dwelling insects including false wireworm but their numbers are rarely sufficiently high to control populations.
Cultural control
  • Use press wheels at sowing to increase compaction of soil around the germinating seed to increase seedling vigour and reduce the movement of FWW larvae in the soil.
  • Bury or destroy stubble before the beetles lay eggs in early summer to reduce adult survival (physical injury and exposure to heat).
  • Use higher seeding rates to ‘compensate’ for seedling losses expected from FWW infestations.
  • Where plant stand is thinned by FWW, surviving plants will grow larger and potentially compensate (at least in part) for seedling losses.
Thresholds The thresholds for false wireworm vary and are speculative:

  • Grey false wireworm: 50 per m2
  • More than 25 larvae in 20 germinating seed baits
Chemical control Insecticide control is recommended if the threshold is exceeded.

  • Incorporating insecticide into soil can minimise crop damage
  • Seed dressings are effective against FWW, but may not provide complete protection under high or prolonged pest pressure. In high pressure situations, consider combining seed dressing with rolling to increase protection of the establishing crop.

Impact on beneficial insects

The use of soil-incorporated insecticides (e.g. OPs) for FWW control will have a significant impact on other insects in the soil. These include not only beneficial insects that predate directly on FWW e.g. carabid beetles, but also on those that predate other species like earthmites.

  • Control of adults can be obtained by baiting with insecticide treated cracked grain broadcast evenly over the surface at or immediately after planting.
  • Where broadcasting is not possible, the bait may be laid in trials spaced no more than 2 metres apart.
Multi-pest considerations Other pests e.g. earthmites can also affect crop establishment. Careful monitoring is critical to attribute seedling loss/damage to the correct cause and implement the appropriate management.
Communication
  • Keep a record of soil insect history of fields to help with planning FWW management (no effective post-planting options available)
  • Schedule for monitoring for FWW in September prior to planting canola, or in autumn prior to planting. Earlier checking (in the previous spring) will give time to order seed with insecticide dressing, if necessary.
  • Industry publications provide up to date regional information about pest activity in crops.

Further information

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