Rhizotrogus majalis
This pest is destructive to lawns in the larval stage and feeds on leaves and flowers in the adult stage. This beetle was first found in British Columbia in 2001. It naturally disperses at a rate of about 10 miles per year. In 2012, this species was detected near the Portland airport in Japanese beetle traps, and found infesting a lawn near Sea-Tac Airport by a homeowner in 2015.
Description and damage The adult beetle is a plain brown scarab beetle that measures about 0.5 inch long. Males have an array of antenna that fan out like plates, but females have tiny antennae. Adults feed on a variety of leaves although this damage is not significant. Significant damage is caused by immature beetle, a C-shaped white grub, as it feeds on the root systems under turf. The European chafer grubs feed on the roots, severing the blades from the roots. The grub is white with three distinct and gangly true legs and a bulbous bag at the hind end. It has a good set of mandibles for feeding on roots. Of secondary concern is the damage to a yard caused by raccoons or skunks that dig up and feed on the grubs.
Biology and life cycle European chafer has a single generation in a year. Adults mate and begin laying 20-30 eggs at dusk. The eggs hatch and larvae begin feeding on small roots and work their way up to larger roots. The larvae feed underground all winter. In May, they create a little crater to pupate in and after two to three weeks, the adults emerge.
Pest Scouting Adults begin buzzing about in May-June, sounding like a swarm of bees as they feed and seek mates. Sometimes exhausted beetles are found near porch lights. To monitor for larvae, dig out a patch of sod and look for the C-shaped white grubs in the root zone of the grass. Five to 10 larvae per square foot is the trigger to take action.
Management—cultural
Keeping turf healthy with a good root system is likely to slow the damage to the turf. With more roots to feed on, there are also more roots to keep growing while they feed. Compact, drought-struggling lawns will have a tougher time surviving.
Management—biological
Parasitic nematodes hold some promise for management.
Management—chemical control
See “Beetles” in Table 5:
Chemical Control of Landscape Pests
For more information
Murray, T., G. Stahnke, and E. LaGasa. 2012. Pest Watch: European Chafer. WSU Extension. FS071E. https://s3.wp.wsu.edu/uploads/sites/2070/2013/12/European-Chafer.pdf