Onion root maggot adult

Onion root maggot adult. Pest and Diseases Image Library, Bugwood.org

Updated: April 27, 2021

Maggots

Appearance

  • The larvae are cream-colored, legless, and 1/3 inch long. They cause plant damage.
  • Adults are flies that 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 overwintering pupae.
  • Rotate alliums with unrelated crops to reduce insect problems.
  • Avoid adding fresh manure to the garden.

Wireworms

Potato wireworm
Potato wireworm.  Photo: G. Lively

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
Click beetle
Photo: Joseph Berger, Bugwood.org 

Life cycle/habits

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

Host plants

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

Signs/symptoms

  • They feed on large vegetable seeds prior to or right after germination. They also infest young beet, sweet potato, turnip, and onion plants.
  • 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 create 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.
Potato with a hole made by a wireworm
Potato with a hole made by a wireworm
Potato damage caused by wireworms
Potato damage caused by wireworms

Prevention/control 

Seeds can also be pre-sprouted to give them a head start. Place seeds on a moistened paper towel. Roll up the paper towel, place it in a plastic bag with some holes and set it on top of the refrigerator. Check the germination rate after 5-7 days. When the radicle (new root) begins to develop, remove seeds and plant in garden soil. However, do not pre-soak bean and corn seeds in water. This treatment will make them more susceptible to soil pathogens.

  • 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.