Soil Feeders - Japanese Beetle

JAPANESE BEETLE
scientific name: Popillia japonica

FIELD KEYS
Hosts: Most grass species
Site symptoms: Turf wilting under heat stress despite adequate available moisture. Wilted turf dies in irregular patches. Removed dead or wilted turf reveals grubs feeding at soil - thatch interface down to 2-inch soil depth.
Plant symptoms: Above-ground plant structure shows no obvious damage or other symptoms. Root system shows much feeding damage from the crown down to a 2-inch depth.
Site keys: Sunny locations with consistent soil moisture and moderate soil temperatures and flowering shrubs, fruit-bearing trees, and vegetable or agriculture production in the area.

SPECIMEN ID
Immatures are six-legged white grubs with tan heads that range in size from 1/6 inch for newly-hatched first instars to 11/4 inch for fully-grown third instars. Adults are 3/8 to 1/2 inch beetles with metallic green heads and shiny bronze colored wing covers.

SCOUTING TIPS
JB over-winters as a third instar grub at soil depths of two to six inches which resumes feeding in April and May, pupates, and emerges as an adult 30 days later. These voracious daylight-feeding adults reach maximum numbers on sunny days when temperatures are 70° - 95° F and humidity is low to moderate. Adult numbers can be monitored with lure attractants or with sweep nets at feeding sites on flowering shrubs, roses, or fruit-bearing trees. Grub sampling should begin 3-4 weeks after maximum adult numbers have been seen. JB larva are vulnerable to extremes of temperature and moisture, so in dry years sample in low or wet areas. In wet years, sample at elevated or drier locations. In years following very cold and dry winters, look in areas with a history of damage.

CONTROL STRATEGIES
Cultural: Where possible limit extra watering at vulnerable sites (to increase egg and first instar mortality) starting when adult flights peak. Increase drainage at wet sites and manage turf for maximum root production. Removal of trees or shrubs that exhibit adult feeding is unnecessary; adults can fly up to 5 miles per day.
Chemical: Historically, infested areas can be treated preventively with pesticides. Once regular sampling indicates that the per square foot grub population has reached 8 -10, consider making a curative control application to asymptomatic sites. At more vulnerable or low maintenance sites, applications may need to begin once grubs populations reach 3 - 5 per square foot.

Growth stages: egg - grub (three instars)* - pupa - adult*
* - treatable stages

Life cycle: 1 to 2 year life cycle
Sequence: grub - pupa - adult - egg - grub