February 2018

Weevil takes heads off of coneflowers, sunflowers and other plants

Coneflowers decapitated by head clipping weevil. (C) Jo Ellen Meyers Sharp

All over Indianapolis, coneflowers and sunflowers are losing their heads.

The sunflower head-clipping weevil (Haplorhynchites aeneus) is to blame for the near decapitation of the flowering plants. The shiny black bug is about 1/4-inch long and is distinguishable by the trademark of most weevils — a pointed snout.

With an incredible precision, the weevil girdles the stem an inch or two below flowers in the family of asters and daisies. The top dangles from a thread of plant fiber, not quite severed.

The head clipping is all about sex. Sometimes, if you break open the dangling flower heads, you’ll find mating weevil pairs slurping nectar and rollicking in pollen.

Kansas State University Extension entomologists say the weevils lay eggs in the flower tops. The eggs hatch after the top falls to the ground and the cream-colored grub like larva over winter in the fallen flower head. The adults emerge in mid-July, which is when the decapitation process begins anew.

Head clipping weevil decapitates sunflowers, coneflowers and other blooming plants. Photo courtesy National Sunflower Association

This insect’s lifecycle illustrates why a fall cleanup of vegetable and flower beds is an important practice to control for insects and diseases.

In the Sunflower State, the Kansas entomologists say an insecticide usually is not recommended for the home gardener because the weevil affects only a small number of plants.

In my garden, though, the weevils decapitated all of the coneflowers in one section, after which the stems turned brown. Cut back damaged plants and be sure to remove any lopped-off flower heads.

Fall Master Gardener classes

If you’d like to learn more about identifying insects, flowers, diseases and how to grow your garden successfully, consider signing up for Master Gardener training.

The fall session runs from Sept. 22 through Dec. 8 at the Purdue Extension-Marion County offices, 6640 Intech Blvd., near I-465 and West 71st Street.


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