The Billbug, otherwise known as the horned weevil, appears to be a part of the beetle family and has larvae that look similar to a grub, but it doesn’t identify as either! Beetles’ mouthparts are attached directly to the head whereas the weevil has a snout that the mouthparts attach to. Beetles have antennae that are attached to the head and weevils have theirs attached to the horn. Beetles also lay their eggs in the thatch or soil and weevils lay their eggs inside stems. (Just think, someday you are going to need these fun facts to win at trivia night!) It is these little bits of information that can help you correctly diagnose a problem.
Billbugs are somewhere around ⅜” long when fully grown. Many times you can see them walking across your sidewalk or driveway. The adults cause little to no damage to the turf, however the females cut small holes in the stems of the grass to insert their eggs.
Once the eggs are laid it takes roughly 14 days to hatch into a white legless larvae with a brown head. The first two larvae stages of life (called instars) are spent inside the grass stem. At the end of the second instar the larvae breaks out of the stem and begins feeding on the roots and crown of the plant. A key indicator you may have this larvae living in your lawn is finding white sawdust-looking frass.
Billbug larvae are approximately ¼ to ⅜” of inch long. It usually takes 5-8 weeks for the larvae to complete all three larval instars. Once the larval stage is complete the next stage is the pupae stage. This lasts until around August when you start to see the adult billbug emerge and prepare to overwinter in piles of leaves left in the lawn, or other protected areas like the foundations of buildings.
In Iowa lawns, billbug damage usually goes unnoticed. Billbugs can be difficult to control because most of the time the larvae is protected by living inside the plant. With the use of Merit, a systemic insecticide, the plant will break the life cycle. Using Pyrethroid insecticides can also be beneficial to control the adults as they creep through the grass.
Often times insect damage goes misdiagnosed. If you notice your turf is dying always use a “tug test” by lightly pull on the turf. If sod and grass come up, then you probably have a grub problem. If you have just roots and stems pull up you may have billbug, Sod webworm, or cutworm damage. This test will help you narrow down what you are looking for. If you have any questions don’t be afraid to give me a call.