Watch out for this garden pest on perennials
A relatively new pest to our area is showing up in perennial gardens, wreaking havoc on coneflowers, rudbeckia and other plants.
The sunflower headclipping weevil is a common pest in the Great Plains and can be a real problem on native plants such as compass and cup plant and prairie dock.
Ohio State University retired entomologist Dr. Dave Shetlar identified this weevil on coneflowers in the Dayton area several years ago. Joe Boggs, Hamilton County Extension Educator and entomologist, also found it on a coneflower field in Yellow Springs.
Since then it has shown up extensively in Miami Valley gardens causing damage to plants in the aster family.
The tiny (one-quarter inch) weevils are shiny and black to copper-brown. As with all weevils, they have a long curved snout which you can see without a hand lens.
The females use their mouthparts (at the end of their snout) to chew around the stem. They don’t chew all the way around, but just enough so that the stem eventually breaks.
The result is a dangling flower, hanging on slightly to the main stem. The female then lays her eggs into the dangling part of the stem. Pay attention to this statement as it is key to control of this pest.
The flower head eventually falls and the rest of the stem remains on the plant, without flowers.
The eggs hatch in the flower portion and the larvae then feed on the decaying flower tissue. They crawl to the soil and overwinter, pupate in the spring and start all over again the next season.
The resulting damage is more aesthetic than anything else. Unless of course, you are growing coneflower for seed production.
Pesticides are not recommended for control. First of all, spraying for the adult weevil is a problem because the flowers are in bloom when the adults are present.
Pesticides labeled for use on flowers specifically state: “This pesticide is highly toxic to bees. Do not apply this product when bees are active.” The pesticide label is the law and gardeners should read and follow all label instructions.
In addition, systemic insecticides won’t kill the larvae because they feed in the part of the plant that is on the ground.
The best method for control refers to the above statement regarding the dangling flower head. Hand pick and remove these flower heads as soon as you see them or after they fall to the ground.
Is this a pain in the rear end? Yes, but as you walk your gardens in the evening with a glass of wine in one hand, simply pay attention to the coneflowers and other plants in this family and hand pick the danglers.
Don’t leave these danglers in the garden but rather drop them in a bucket of soapy water or dispose in the trash. 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.