Wireworms

Causal Organisms: Agriotes obscurus (Dusky / European Wireworm); Agriotes mancus (Wheat wireworm)

Crops Affected: potatoes, tomatoes, cucurbits, carrots, parsnips, maize (sweet corn), eggplant, peppers, small grain cereals (barley, wheat), etc.

Life Cycle:

• Adults are click beetles
  • They do not attack potatoes
• Adults emerge in the spring and lay eggs in the soil near grass roots
• Larvae are glossy brown or brownish white and slightly darker at one end
  • Larvae may reach 1.2 inches (3 cm) in length and are flexible but tough-bodied
  • Larvae mature over several (3-5) years, moulting about 10 times
  • Early stage larvae do little damage
  • As larvae mature, they become more voracious, feeding on any underground plant parts
• Larvae can tolerate a period of starvation once one season of development has occurred
  • Move vertically within the soil in response to moisture, temperature and to find food
  • In fields with root crops (e.g. carrots and potatoes), wireworms tend to spend much of the growing season in the top 4 inches (10cm) of the soil profile
• Wireworms thrive in grasslands
  • The most severe damage from wireworms occurs in crops grown following a pasture
  • Wireworms prefer cereal crops
  • Wireworms do not like weed-free alfalfa

Symptoms:

• Damage will be more severe in land that has recently been converted from pasture or grassland
• In corn
  • An irregular pattern of plants dying in the field, or weak or poorly vigorous plants may be observed
  • Larvae bore into seeds or enter the underground stem
• In potatoes
  • Larvae burrow into seed pieces and developing roots and shoots
  • Spotty and weakened plants may be observed
  • Larvae will also feed on developing tubers
    • Holes that are 3mm diameter up to 4cm deep may be found
    • Holes will be lined with wound periderm tissue and tubers may be distorted
  • Larval feeding can provide a point of entry for blackleg and Rhizoctonia diseases in potatoes
  • Damage by wireworm feeding renders potatoes unmarketable

Monitoring:

• Wireworms detect carbon dioxide while searching for food
• The use of baits can be an effective monitoring tool
  • Monitoring using bait is best done prior to planting a crop
    • Monitor in fall prior to frost, or in spring once temperatures climb above 5-10°C
  • Bait may be grain corn and wheat that has been moistened to begin germination, cut up potato or carrot pieces, or one cup of flour
  • Bury bait 4-6 inches (10-15cm) in the soil and mark with a flag
  • Use several bait stations randomly placed throughout the field (30-50 per hectare)
  • Check stations every 2 weeks for the presence of larvae
  • Monitor stations until larval activity is detected or until early September
  • Excessively wet or dry soil will reduce the efficacy of the baits, as will cold soil or soil that contains a lot of plant residues

Management:

• Monitor to determine degree of infestation
  • 1 or more wireworm larva per bait station can lead to severe potato damage
• Shallow cultivation while larvae are young can expose them to predators (birds, etc.)
• Avoid planting into land that has recently been broken
• Use care when moving machinery from infested fields to new fields
• Rotations can reduce early population development but once larvae develop at least one season, rotating for population management will become less effective
• Growing certain cover crops in a rotation can have positive effects on reducing the population
  • Brown mustard or buckwheat can be effective
  • Mustard should be incorporated prior to going to seed, allowing its natural bio-fumigant properties to take effect