Insect of the Month - Carrot Weevils

  Hort Snacks - May 2017
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 Listronotus oregonensis

Crops Affected: carrot, parsnips

Life Cycle:

  • Overwinter as adults in soil, in and around infected carrot fields from previous season
    • Move into new crops in spring to feed on foliage
  • Adults are approximately 0.25 inches (6 mm) long, with a dark brown body and a snout
    • Females chew holes in the petiole or crown, lay 2-3 eggs and seal the hole with black exudate
    • Eggs are generally laid on petioles when plants reach the 4 leaf stage
    • Eggs hatch one to two weeks after being laid
  • Larvae are grub-like, with a reddish brown head
    • Larvae tunnel into the main root, feeding in the upper portion of the root
    • Larvae feed for minimum of 3 weeks, then move out of the carrot to pupate in soil
  • Adults emerge after 1 to 2 weeks
  • Typically only one life cycle per year
  • Tunnelling into petioles, heart, crown or centre and root of affected plant
  • Scarring of root in top 1/3, rendering it unmarketable
    • May be distinguished from Carrot Rust Fly damage, which typically occurs in the bottom 2/3 of the root
  • Distinctly weevil-like adults may be seen early in season, feeding on petioles
  • Wooden plate traps can be used to monitor adults
  • Chunks of carrot may also be placed in the soil
  • Adults rarely fly, so infestations may be localized and take number of years to build up to levels of concern
  • Monitor traps and apply registered products at appropriate times
  • Parasitism by Anaphes sp. may offer significant control in some regions and should be encourages as much as possible

Carrot weevil pupa, left; larva, right.
Carrot weevil, adult
Photo by OMAFRA
Photo by Alton N. Sparks, Jr., University of Georgia,
Wooden plate trap and carrot traps
Carrot weevil larvae and damage
Photo by OMAFRA
Photo by Whitney Cranshaw, Colorado State University,
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This information published to the web on April 27, 2017.