University of Maryland Extension

Wireworms and Maggots - Vegetables

Wireworms

onion maggot adult fly
Onion root maggot adult 

Appearance

  • The larvae are cream colored, legless and 1/3 inch long. They cause the plant damage.
  • Adults are flies which lay eggs on plants.

Life Cycle/Habits

  • Corn seed maggot, onion root maggot, and wireworms cause similar problems.
  • Adult flies emerge in spring and mated females lay eggs at the base of plants. Larvae hatch and tunnel into stems and enlarging bulbs.
  • Larvae hatch and tunnel into stems and enlarging bulbs.
  • Larvae pupate in the soil near infested plants.
  • There are 2-3 generations per year.

Host Plants

  • This is a common pest of allium family members.
  • Shallots are most vulnerable followed by onions and garlic.

Signs/Symptoms

  • Infested plants wilt or turn yellow and die.
  • A single larva can damage several plants.

Prevention/Control

  • Where this insect has been a problem, use floating row cover to prevent adult flies from depositing eggs.
  • Pull and destroy affected plants.
  • Keep weeds down to eliminate habitat for adult flies.
  • Remove all plant debris and till the garden in the fall to expose and destroy over-wintering pupae.
  • Rotate alliums with unrelated crops to reduce insect problems.
  • Avoid adding fresh manure to the garden.

Wireworms

potato wireworm
Potato wireworm

Appearance 

  • They are slender, shiny, tough-skinned worms with pale yellow to reddish-brown bodies.
  • Wireworms can grow to over 1 inch in length.
  • The adults are click beetles. 

click beetle adult
Click beetle
Photo: Joseph Berger, Bugwood.org 

Life Cycle/Habits

  • The larvae spend 1-6 years in the soil.

Host Plants

  • Potatoes and beet roots. They also infest sweet potato, turnip, and onion.

Signs/Symptoms

  • They make many small holes in tubers and beet roots.
  • Fresh holes have ragged edges and contain chewed root tissue.
  • Wireworms can damage potato seed pieces, opening them to fungal and bacterial infections that result in weak plants.
  • They bore into developing tubers, leaving round holes about 1/8 inch in diameter and making the tuber look like it has been punctured with a nail.
  • The tunnels may be shallow or deep and go straight into the tuber.
  • Injury is more noticeable late in the season, during dry seasons and where turfgrass was recently converted to a vegetable garden.

hole in potato from wireworm
Potato with a hole made by a wireworm

inside of damaged potato
Potato damage caused by wireworms

Prevention/Control 

  • Rotate susceptible crops.
  • Till garden soil prior to planting in spring to kill and disrupt larvae.
  • Plan to dig and eat new potatoes rather than growing storage potatoes.
  • To reduce wireworm populations, spear pieces of potato or carrot on a stick and bury them 2 to 4 inches deep in the garden. Dig up the pieces after a week and destroy them, along with the wireworms that are feeding inside. Set the potato traps at 3 to 10 foot intervals.

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