Hollyhock Weevils Cause Reduced Flowering
Hollyhock is a well-adapted, drought tolerant plant with beautiful spires of summer flowers. It is typically a biennial or short-lived perennial. To maintain a healthy flower population plants should re-seed every year. If a hollyhock planting is not re-seeding well, it may be harboring a population of hollyhock weevils.
The hollyhock weevil (Apion longirostre) is a common reason for hollyhock patches to thin out, or not re-seed a healthy replacement crop. This small insect is approximately 1/8” – 1/4” long (which includes the long snout). Weevil snouts are adapted for chewing, with the jaw located at the tip of the snout. The snout of the female is almost as long as the body while the male snout is about half as long. The jointed antennae are located halfway along the snout. The tiny gray body is slightly hairy and the legs are yellow/orange.
Hollyhock weevil adults overwinter in the soil and duff of the hollyhock flower bed. They emerge in spring and chew irregular holes in new leaves, which is a good early indicator of activity. When the flower buds appear, the adults move up the plant and can be easily seen. They are most active at night. The female chews holes deep into the flower bud with her long snout and lays an egg in each hole. A normal flower develops, but the tiny larvae will feed inside the seed embryo and eventually consume the seed that forms from the inside out. They pupate in the seed head and the new adults will emerge about August and drop to the soil to overwinter.
Control options include mechanical and chemical practices. Scout for weevils by checking new growth on plants in the spring. The nice thing about hollyhock weevils is that they are quite host-specific—you probably won’t find them on other landscape plants.
Hollyhock weevils are easily disturbed. Place a cloth under the plants and shake them down. Destroy the fallen weevils by crushing or dumping them in soapy water. Check for infested seeds and destroy them before the adults emerge.
Chemical options include soft approaches such as insecticidal soap or horticultural oil. Pyrethrin, Sevin, Orthene, or Malathion may be used as a last resort. Spraying will be most effective if done in late evening. Keep in mind that broad spectrum insecticides may also kill beneficial insects.
-Ron Patterson, Extension Assistant Professor