Head-Clipping Weevils Devastate Coneflowers, Sunflowers, Other Aster Family Members

Head-clipping weevils can cause major destruction in a pollinator garden, so here's what to look for and how to stop Haplorhynchites aeneus in its tracks.

by Susan Brackney
PHOTO: images by Susan Brackney

I rely on native perennials like purple coneflower and black-eyed Susans quite heavily in my landscape because they’re so drought-tolerant and generally very forgiving. They spread out nicely over time, support lots of different bees and butterflies, and attract sundry birds with their seed heads in the late summer and fall.

Once I mix in perennial common milkweed along with annual zinnias and assorted sunflowers, I’m left with a solid, worry-free pollinator garden. At least that’s how things used to be.

Recently, I noticed several of my new purple coneflower heads were drooping. At first glance, I thought the heat and dry conditions that so many of us have been suffering through lately were bad enough to affect even my drought-tolerant coneflowers. Then I looked more closely. I could barely believe my eyes.

While several other coneflower heads on the same plant looked as perky as ever, their droopy counterparts seemed to have been cut nearly all the way through and were now hanging by a thread. Worse still, when I stood back to take in the whole scene, I saw that several of my echinacea plants had been reduced to mere stems.

Had someone helped themselves to a cut-flower bouquet? Nope.

Looking down, I saw the cut flower heads shriveled up (or in the process of shriveling) lying on the ground below. Then I noticed that some of my sunflowers—finally beginning to bloom, no less!—similarly had been snipped.

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Weevil Woes

Turns out a very small insect created my big mess. Known as the head-clipping weevil, the head clipper weevil or, sometimes, the sunflower head-clipping weevil, the insect is officially classified as Haplorhynchites aeneus. And there’s still a lot we don’t know about it.

According to the National Sunflower Association, “Work on this insect has been very limited due to its lack of economic injury.”

But here’s what we do know. These tiny black creatures have long, beaklike mouthparts with which they can slice through hollow-stemmed plants like my purple coneflowers and sunflowers. (Head-clipping weevils are also drawn to important prairie plants such as prairie dock, compass plant and prairie asters, among others. As such, you’re most apt to find head-clipping weevils in parts of the Midwest and Great Plains. However, their range may be shifting.)

So, what’s behind all of the flower head-clipping destruction? Think of it as a precursor to “date night.” After the female and male head-clipping weevils mate, the female deposits her fertilized eggs in the damaged flower head. Eventually, the eggs hatch, the weevil larvae eat the old flower head from which they emerged, and then they burrow deep into the soil below. There, they’ll overwinter until the next growing season when new blooms have come on.

head-clipping weevil

Facilitating this lifecycle seems awfully costly. Certainly, there is the lost personal enjoyment from so many missing blooms.

But, to my mind, it’s more than that. There’s the resulting lost pollen and nectar that our foraging pollinators so desperately need. And then there are all of the birds who have come to rely on the spent seed heads that I’ll leave until well into late spring. If enough weevils survive year after year, my wildlife garden won’t be able to support nearly as many animals and beneficial insects as it once did.

Protecting Plants

Fortunately, we all have some recourse when it comes to controlling these unusual insects. If you have head-clipping weevils, first take a close look at any affected plants to try to catch the culprits at work. Slicing through tough stems takes time and effort for these insects, so you just might get lucky.

In particular, examine the first inch or two below your flower heads. You might notice the start of a dark, horizontal line or a series of puncture marks girdling the stem. Then, you might see the insect itself. If so, hand-pick and drop it in a container of soapy water. (Just keep in mind that they can fly, so you’d better be swift as you grab them!)

You’ll also want to pick up any dropped flower heads you see, since these will eventually play host to the next generation of head clippers. Rather than compost these flower heads, wrap them up and throw them away. (Alternatively, you could solarize the flower heads and then place them well away from any potential host plants.)

Finally, use clean, sharp garden shears to remove most of the stem from any previously clipped flower heads to facilitate plant bushing and stimulate the production of new blooms.

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