Japanese Beetle
Popillia japonica
0 host plants
Last updated
Quick Reference
Japanese Beetle Adult emergence typically begins around 3485 GDD₃₂. As of April 17, 2026, Puget Sound stations range from 1302.4 to 1445.4 GDD₃₂, approximately 2040 units before the expected threshold.
Regional Season Tracker
GDD₃₂ accumulation across 7 Puget Sound stations · as of Apr 17, 2026| Station | GDD₃₂ | Current Stage | Next | To Go |
|---|---|---|---|---|
| Issaquah / East King | 1,445 | Pre-season | Adult emergence | 2,040 |
| Seattle / UW | 1,417 | Pre-season | Adult emergence | 2,069 |
| Kent / Auburn | 1,385 | Pre-season | Adult emergence | 2,100 |
| Olympia / Tumwater | 1,363 | Pre-season | Adult emergence | 2,122 |
| Bellingham / Whatcom | 1,343 | Pre-season | Adult emergence | 2,142 |
| Tacoma / Puyallup | 1,328 | Pre-season | Adult emergence | 2,157 |
| Sequim / Rain Shadow | 1,302 | Pre-season | Adult emergence | 2,183 |
GDD source: UMD IPMnet Pest Predictive Calendar (Gill & Klick). Base 50°F, mid-Atlantic climate. Converted to GDD₃₂ for Western WA. About GDD₃₂ →
Monitoring & Action
Pheromone/floral lure traps (dual-lure combining sex pheromone and floral attractant). Note: traps attract more beetles than they catch and may increase local damage within approximately 30 feet of the trap; place traps well away from valued plants. Traps are useful for detection and population monitoring but are not effective as a control method (OSU EM 9158). Visual inspection for adults on preferred hosts in morning hours. Turf scouting: cut 1 sq ft sections of turf and count grubs. WSDA and ODA deploy thousands of monitoring traps annually (ODA placed 10,272 traps statewide in 2024).
In PNW: any confirmed detection warrants immediate reporting to WSDA (WA) or ODA (OR); this is a quarantine pest in both states. For established populations (eastern US reference): adult feeding on high-value ornamentals warrants intervention when defoliation exceeds 15-20% on non-recovering hosts. Grub threshold in turf: 10-12 per sq ft.
Adults skeletonize leaves by feeding on tissue between veins, leaving a lace-like pattern of intact veins. Also feed on flowers (especially rose petals) and fruit. Aggregation behavior driven by volatile compounds released by damaged foliage causes beetles to congregate, resulting in severe localized defoliation of preferred hosts. Larvae feed on grass roots in the upper 2-3 inches of soil, causing brown patches in lawns that detach from the soil and can be rolled back like carpet. Heavy grub infestations attract secondary turf damage from skunks, raccoons, crows, and starlings digging for grubs. (OSU EM 9158; ODA)
Cultural Controls
- Report all sightings to state agriculture department
- Hand-pick adults from plants
- Reduce or eliminate lawn irrigation during egg-laying and early grub period
- Select less-preferred plants in new plantings near known infested areas
- Do not use pheromone traps for beetle control
Japanese beetle is under active eradication in both Oregon and Washington as of early 2026. In Oregon, the largest infestation was discovered in 2016 in the Cedar Mill, Bonny Slope, Oak Hills, and Bethany areas of Washington County; smaller populations later found in Clackamas and Multnomah Counties and at Portland International Airport. ODA trapped 1,918 beetles statewide in 2025, a 65% decrease from 2024 and a 92% reduction since 2016 peak. ODA treats approximately 4,500 properties annually across ~1,300 acres with chlorantraniliprole (Acelepryn G). Oregon HB 5204 allocated $1.8M for the 2026-2027 program. In Washington, WSDA trapped 72,626 beetles statewide in 2025, nearly 3x the 2024 count. The epicenter is the lower Yakima Valley (Grandview area: 68,237 beetles). Critically for Western WA, 865 beetles were trapped in SeaTac in 2025 (up from 32 in 2024), triggering the first Western WA eradication treatment for 2026 (1,350 King County properties). This is the nearest confirmed reproducing population to the Puget Sound lowlands. Report sightings to WSDA at agr.wa.gov/beetles or 1-800-443-6684; in Oregon to ODA at oregoninvasiveshotline.org or 1-866-INVADER.