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Sunflower stem weevil

Cylindrocopturus adspersus[3]

The sunflower stem weevil is a small, white-spotted weevil whose larvae tunnel inside sunflower stalks and overwinter at the base; the weakened stalks break and lodge before harvest, especially in drought or high wind.[1][2]

Group
Insect
Order
Coleoptera
Family
Curculionidae
US records
15 states
Sources
3 cited
Updated
2026-10-19

No licensed photo of this species is available yet; the identification notes below describe what to look for.

On this page
  1. Identification
  2. Look-alikes
  3. Where it lives
  4. Biology
  5. Damage and signs
  6. Health risk
  7. Control
  8. Related profiles
  9. Common questions
  10. Sources

How to identify it

  • Adults are about 3/16 inch (4 to 5 mm) long, grayish-brown and covered with irregular white spots, with a beak tucked under the head.[2][1]
  • Larvae are found tunneling in the stalk pith, and in fall in chambers at the base of the stalk or root crown.[2][1]

Look-alikes

Look-alikeHow to tell them apart
Dectes stem borerAnother sunflower stalk borer that also causes lodging; its larvae are cannibalistic, so a stalk usually holds only one, while dozens of stem weevil larvae can share a stalk.[2]

Where it lives

It is an economic pest of cultivated sunflower across the northern and southern Great Plains and into Saskatchewan, with occasional severe losses in western Kansas, eastern Colorado and the Dakotas.[2][1]

US map: public records from 15 states since 1990 (GBIF).

Biology and life cycle

Adults emerge from last year's stalks and root crowns in early to mid-April in the southern Plains and mid to late June in the northern Plains; a degree-day model can predict emergence.[2][1]

Females lay eggs under the epidermis at the base of the stalks; the larvae feed in the vascular tissue, then tunnel into the pith.[2][1]

By late August the larvae move down to the lower stalk or root crown and dig overwintering chambers, pupating the following late spring.[2][1]

Damage and signs

  • Adult feeding on stems and leaves is minor; the real loss is lodging, when stalks weakened by tunnels and chambers break before harvest. In North Dakota, an average of 38 larvae per stalk produced 28 percent lodging.[1][2]
  • Breakage is worst in drought or high winds as plants dry down.[2]

Health risk

It feeds only on sunflower; Colorado State and the University of Minnesota text mention no risk to people.[1][2]

Control

Prevention

In northeastern Colorado, planting after June 1 reduces the risk, and thinner stands grow thicker stalks that resist lodging.[1]

Sanitation

Fall tillage that destroys the overwintering chambers at the stalk base helps, though it may conflict with soil conservation.[1]

Pesticides

Foliar insecticides control adults but not larvae already inside the stalk, so timing matters; the economic threshold is about one adult per three plants, with sprays timed around the 8- to 14-leaf stage.[1][2]

Common questions

Why are my sunflower stalks snapping before harvest?
Sunflower stem weevil larvae are one possible cause; their tunnels and overwintering chambers weaken the stalk base.[1][2]
When do I need to treat sunflower stem weevil?
When adults reach about one per three plants and before eggs are laid, since sprays don't reach larvae inside the stalk.[2][1]

Sources

  1. Colorado State University Extension, “Sunflower Stem Weevil Management.” extension.colostate.edu/resource/sunflower-stem-weevil-management (accessed 2026-10-19)
  2. University of Minnesota, “Sunflower Insect Pest Management in North America (L. D. Charlet et al., Radcliffe's IPM World Textbook).” ipmworld.umn.edu/charlet (accessed 2026-10-19)
  3. iNaturalist, “Cylindrocopturus adspersus taxon page (order and family).” www.inaturalist.org/taxa/304317 (accessed 2026-10-06)

Updated 2026-10-19. Built from sourced records. Spot an error? Tell us.