University of Maryland Extension

Wireworms and Maggots - Vegetables

Back to Common Problems - Vegetables

Onion Root Maggot, Seedcorn maggot, Wireworms

Onion Root Maggot

onion maggot fly

This is a common pest of allium family members. Shallots are most vulnerable followed by onions and garlic. Adult flies emerge in spring and mated females lay eggs at the base of plants. Larvae hatch and tunnel into stems and enlarging bulbs. A single larva can damage several plants. The larvae are cream colored, legless and 1/3 inch long. Infested plants wilt or turn yellow and die. Larvae pupate in the soil near infested plants. There are 2-3 generations per year.

Management: 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.



wireworm damage to inside of potato


Wireworms are slender, shiny, tough-skinned worms with pale yellow to reddish-brown bodies. They can grow to over 1 inch in length. The adults are click beetles. The larvae spend 1-6 years in the soil. They make many small holes in tubers and beet roots. They also infest sweet potato, turnip, and onion. 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.

Management: 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.

Photo Gallery:

hole in potato from wireworm

wireworm hole

potato wireworm maggot

potato wireworm

click beetle and larvae

click beetle wireworm

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