Have you ever wondered which pest may be responsible for your sunflowers and purple coneflowers being beheaded? Flowers that are missing heads have become a victim of the dreaded Sunflower Head Clipper Weevil Haplorhynchites aeneus. This Weevil will also attack any plant in the Silphium genus, this includes Compass plants, Prairie Dock, and the Cup plant to name a few.
The Sunflower Head Clipper Weevil is known for clipping heads off wild and cultivated sunflowers throughout the Great Plains and is quite common in Ohio. Aside from the evidence left behind from the Weevil of clipped off flower heads, you can identify the weevil by its black and shiny to brown color, and tell-tale long weevil snout, which is referred to as the “Rostrum,” and includes the mouthparts at the tip. The weevil measures a little over one-fourth inch in length. If you have a significant patch of purple cone flowers that have been decapitated, the stems will resemble straws, we call this “soda Straw” Damage.
The female weevils are whose to blame for the cutting of the heads. She will insert her snout into the flower stem chewing a ring of holes around the stem below the flower head, this causes the stem to break, and the head will be holding on by a thin strand of tissue. The female weevil then lays her eggs in the flower head and the head falls to the ground. After the flower head falls to the ground, the eggs will hatch into a grub-like larvae which will feed on the decaying flower head tissue. After the larvae feed on the flower head, they bury themselves in the ground to over-winter, and appear again as adults in late June to early July.
Even in sunflowers that are cultivated as an agronomic crop rarely see enough Sunflower Head Clipper Weevils to justify a pesticide application for mitigation, but if a farmer was to reach threshold of 10% or greater of heads being clipped off, an application of pesticides aimed at controlling the Sunflower Moth will also afford some control of the weevil.
For the home garden, mitigation is as simple as removing and throwing away the flower heads that have fallen to the ground. This will take the eggs or larvae that are still inside of the head away from your garden, over time this will deplete the population as they will not have a chance of over-wintering in the soil. Insecticide labels will not recommend making an application to plants in flower because of the risk of killing plant pollinators. Remember that the pesticide label is the law.
For more information on the Sunflower Head Clipper Weevil, visit bygl.osu.edu
Brooks Warner is the Ag & Natural Resources Educator at OSU Extension Clinton County.
