Carrot Weevil

Host Plants

Adult carrot weevils and their larvae feed on carrots and other plants from the carrot family, including parsnip, parsley, and celery.

Regions impacted

Found throughout North America, with particular presence and damage in regions around the Great Lakes in the US and Canada.

Description

Adult carrot weevils are small dusty-brown hard-shelled beetles, about 1/6th of an inch (6 mm.) long. They have a distinctive snout used effectively to feed on carrots and related plants. They walk from host to host. Eggs begin white and slowly darken to black as they mature. The larvae are cream-colored leg-less grubs or maggots sporting a light brown head. The pupae are similar in color to the larvae.

Life Cycle

• Adult carrot weevils overwinter in grass debris or topsoil, emerging in spring.
• They begin mating after several warm days, and females lay eggs on plant stems or crowns by the end of May. The females make small holes, deposit two to three eggs in each, and cover with a secreted fluid for protection.
• Eggs hatch after one to two weeks, and the young larvae proceed to tunnel down into the root Young plants may wilt and die as a result. After going through four instars, the larvae then pupate, and adults emerge in midsummer.
• Carrot weevils can complete one to two generations per year.

Damage and Detection

• Adult carrot weevils feed on the foliage of carrots, parsley, and parsnips but generally do little serious damage.
• The larvae, however, are a different story. Once hatched, larvae burrow through the roots of the plants and can do serious damage.
• Larvae are well hidden inside the host, making detection, let alone treatment, difficult.
• Tunneling can stunt and often kill the host resulting in serious crop loss.
• Weevil damage will become apparent as darkened, opened tunnels in the upper third of the root, marking an exit tunnel for the satiated larvae.

Prevention and Control

Monitoring for potential infestation is challenging because the adults, larvae, and eggs are well camouflaged.

To augment the difficult chore of physical inspection, Boivin traps can be used. This trap attracts the pest using a carrot as bait; if, after several days, there are 2 or more weevils in the trap, there is a potential infestation problem. Options for containment are below:

Cultural controls

• Crop rotation is important since carrot weevils overwinter in the location where carrots grew the previous year. Move the patch every year and try not to return to that location for three or more years, if possible.
• If possible, delay planting until mid-June, when the bulk of first-generation adults will have died.
• Maintain a clean and weed-free garden to control hiding places in which to overwinter.
• hand-pick insects and/or use floating row covers to keep the adult beetle from reaching its host.
• Rather than harvesting or picking a carrot randomly, try to harvest entire sections or rows at a time
• Traps can be effective. They can be bought at garden centers or be hand-made with a few mason jars and paper cups. Poke holes in the bottom of a paper cup and fit them into the top of the mason jar. Bait with slices of carrots and larvae can find their way in but not out.

Biological controls

• Milky spores and Bacillus thuringiensis (Bt) are organisms that kill larvae without harm to other creatures. They will be more effective when applied early; they have little impact on mature larvae.
• Use neem-based sprays on older larvae.
• Several species of parasitoid wasps will attack eggs and can be helpful in the smaller gardens.

Insecticides

Adults are reasonably susceptible to chemical treatments, and larvae are safely tucked away in the roots. Although chemical pesticides are available for home use, efficacy is low, and damage to other insects likely outweighs any benefits.