Sunflower head-clipping weevil damaging perennials

I have had numerous calls recently regarding sunflower and coneflower blooms breaking off just below the flowers. While this pest has been around for several years, it’s becoming more and more common in home landscapes.

The damage is the result of the sunflower head-clipping weevil. The female weevil chews a ring of holes around the stem, just about one or two inches below the flower.

This doesn’t completely damage the stem, however, it’s eventually weakened enough that it topples over, remaining attached to the stem by a thread of tissue.

Mating occurs on the flower head and eventually the female lays her eggs. Currently, they are in the mating and egg laying phases around here. I haven’t seen any eggs or larvae in the heads as of yet.

The female lays her eggs in the flower head, which eventually falls to the ground. The eggs hatch into the larva that sort of looks like a grub, except that it doesn’t have legs.

The larvae feed on the dying flower that’s laying on the ground. They move into the soil and spend the winter as larvae. In the spring, they pupate and the adults emerge. We start seeing the damage around the beginning of July.

Control of this pest is rather challenging for a few reasons. First of all, insecticides are not effective. You may attempt to control the adult weevil which means that you have to target the flower and stem.

This is not recommended during bloom because of the many pollinators that visit these flowers during the day. I try to avoid spraying my coneflowers with pesticides during bloom.

Second, a systemic insecticide won’t work because the female isn’t feeding on the stem. She is only using it as a mechanism for laying eggs.

“The larvae feed on the dying flower that’s laying on the ground.” I am repeating this sentence as this is the clue on how to control the sunflower head-clipping weevil.

If the larvae are spending time in the flower head, feeding and getting fat and happy, why not eliminate as many of them as possible with hand removal.

Unfortunately, this is one of the best methods of control and thus reduces the populations for next season.

Hand-pick those flowers that are broken over and carefully drop them in a bucket of soapy water. This helps to eliminate as many adults as possible prior to egg laying.

Once they are on the ground, pick up the dead flower heads and dispose of them as well. In the fall, be sure to clean up as much debris as possible.

I know that this isn’t an easy control method, but it keeps our pollinators safe (no pesticides while blooming) and decreases or minimizes the population next season.

Fortunately there is only one generation per year. They also affect some of our native plants such as compass plant and prairie dock.