(Posted Aug. 12, 2021)
By Jane Kutzley, Madison County Master Gardener
A native insect getting some attention lately is the sunflower head-clipping weevil, one of the silphium weevils (as they are most active on plants in the silphium genus).
Head-clippers have been expanding their range in recent years and, unfortunately, can now be found in central Ohio.
The sunflower head-clipping weevil does exactly what its name implies, except it is interested in lots more than just sunflowers. Coneflowers, compass plant, prairie dock and all members of the aster family are the most attractive to head-clippers. The weevil is about one-quarter-inch long and either shiny black or bronzy-brown. The snout is more elongated than most weevils.
The mode of action for this insect is simple and effective. The female chooses a flower in full bloom, then inserts her snout into the stem an inch or several below the flower. She chews a ring of holes around the stem and may ultimately make several rings around the stem at varying distances from the flower head. Eventually, the stem is so weakened it breaks. The flower head is left dangling by thin bands of unchewed tissue.
Once the flower head is dangling, the weevil and many of her friends lay eggs on it. Soon, the flower head falls to the ground, leaving behind stems that stick up like soda straws. Once on the ground, the weevil eggs hatch and begin feeding on the decaying flower head. Ultimately, the larvae drop to the soil and burrow in to spend the winter. The cycle starts over in late June or July when the adult weevil leaves the soil.
Control by removal is the best practice. Dangling flower heads should be cut off below the bend and disposed of (do not compost). Clean up fallen heads quickly. The goal is to prevent reinfestation. Insecticidal sprays are not an option because more vulnerable and desirable pollinators will be harmed.