These weevils are a new pest

Pamela Corle-Bennett is the state master gardener volunteer coordinator and horticulture educator for Ohio State University Extension. Contact her by email at bennett.27@osu.edu.

My Ohio State University Extension colleagues and I are hearing more and more about damage to coneflowers and other plants in this family caused by a pest in our area called the sunflower head-clipping weevil.

The damage is easily recognized and is how this pest got its name: The tips of the flowers simply flop over as a result of feeding damage.

Though this pest is kind of new to our area, it’s been around and is well known in the Great Plains, where it causes damage to both wild and cultivated sunflowers.

Around five or six years ago, one of my entomology colleagues got a call from someone in Greene County who was noticing this problem in a large field of coneflowers. All of the blooms were flopped over, just barely hanging from the flower stems.

Since then, we have been hearing more and more about it around the southern and western part of the state.

This weevil prefers sunflowers but will also feed on coneflowers as well as other plants in the aster family.

The sunflower head-clipping weevil, as with all weevils, has a curved snout. The mouthparts are located at the end of the snout.

The females chew a ring of holes around the flower stem; this is usually around 1 to 3 inches below the bloom. This weakens the stem to the point where it eventually breaks over, leaving the flower hanging by a thread.

Here is an important key in controlling this pest. The females lay eggs on the flower head; the larvae hatch and feed on the flower head.

The larvae continue their development in the flower head and then drop to the ground to overwinter. Next spring they pupate and the adults emerge and begin to feed again.

By removing the flower heads that are still hanging as well as those that have dropped to the ground you can help to reduce populations next year.

When removing the flowers from the stem, hold a bucket of soapy water under the flower and clip the rest of the stem, dropping the flower into the bucket.

This may help to kill any adults that are feeding in the flowers, reducing the populations and further damage to other plants. It also kills the larvae and prevents them from further developing.

This is the best control method for the sunflower head-clipping weevil. Pesticides are not a good option. Pesticides should not be used on a plant in full bloom because of the risk of killing pollinators.

I am curious as to its location around the Miami Valley. If you are seeing this type of damage to your coneflowers, sunflowers or even compass plants, let me know by sending me an email message at bennett.27@osu.edu.

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