Asian Longhorned Beetle: What to Do in September

September marks the tail end of a long, damaging season for one of North America's most destructive hardwood pests. The Asian Longhorned Beetle (ALB) — identified by USDA APHIS as a significant pest threat — is a wood-boring insect that tunnels deep into the trunks and branches of hardwood trees, compromising their structural integrity from the inside out. If you have maples, elms, willows, birches, or other hardwoods on your property, this month deserves your attention. Check our seasonal forecast for a full picture of what's active in your region right now.

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Why September Matters for This Threat

Based on typical activity patterns, Asian Longhorned Beetle is most active between May and September. That means right now — in September — you're in the final stretch of peak activity season. Adult beetles that emerged earlier in the summer have had months to feed, mate, and lay eggs beneath tree bark. Those eggs are now hatching into larvae that will burrow deeper into wood tissue, where they are far harder to detect and treat.

Acting in September gives you a critical window: adult beetles may still be present and vulnerable to treatment, and early larval infestations can still be addressed before insects overwinter and cause further damage next year. Waiting until spring means another full season of tunneling goes unchecked.

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What to Look for Right Now

Asian Longhorned Beetle damage is distinctive once you know what to look for. Walk your property this month and inspect your hardwood trees closely for the following signs:

• Round exit holes in bark — roughly the size of a dime — where adult beetles have emerged
• Sawdust-like frass (wood shavings and excrement) collecting at the base of trees or in bark crevices
• Oozing sap or staining on trunks and major branches
• Dead or dying branches in the upper canopy, sometimes called "flagging"
• The beetles themselves — large, glossy black insects with distinctive white spots and very long, banded antennae

Not sure what you're seeing? Use our diagnosis tool to upload photos and get guidance based on your symptoms and location.

For a complete breakdown of this pest's biology and identification markers, visit the full details page.

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Where It's Active

This pest is currently tracked as active across all 50 U.S. states, reflecting the widespread concern that land managers and regulatory agencies have about its potential spread. USDA APHIS has designated Asian Longhorned Beetle a pest threat of national importance, meaning established populations in any region should be taken seriously and reported promptly to local agricultural authorities.

Whether you're in a densely wooded northeastern state or managing a smaller urban tree canopy in the South or West, the risk of encountering — or inadvertently spreading — this insect through infested firewood or plant material remains real.

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What to Do This Month

September is a month for action. Here's what you can do right now:

1. Targeted Insecticide Application If active adult beetles are present, applying an appropriate insecticide — strictly following label directions — can help reduce adult populations before the season closes. Timing matters enormously with ALB: treatments aimed at adult beetles or newly hatching larvae are most effective. Do not apply insecticides without confirming a positive ID; consult a professional if you're uncertain.

2. Remove and Destroy Infested Material Prune out any branches showing clear signs of infestation — exit holes, frass, or internal tunneling. Do not move infested wood off your property without guidance. Transporting infested logs or branches is one of the primary ways this pest spreads to new areas. Infested material should be chipped, burned (where permitted), or disposed of according to your local agricultural extension recommendations.

3. Encourage Biological Controls Natural predators and parasitoids — including certain parasitic wasp species — can help suppress ALB populations over time. While this is not a rapid solution, supporting a healthy, biodiverse landscape around your trees contributes to long-term resilience.

4. Report Suspected Sightings ALB is a regulated pest. If you believe you've found an infestation, report it to your state department of agriculture or USDA APHIS. Early detection is the most effective tool for containment.

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When to Call an Arborist

Call a certified arborist immediately if:

• You find round exit holes or heavy frass deposits on multiple trees
• A tree shows significant canopy dieback that appeared over a single season
• You're unsure whether your hardwoods are infested and want a professional assessment before the season ends
• You need guidance on safe removal of potentially infested branches or logs

Early professional intervention can save trees that might otherwise require complete removal. Don't wait until next spring — larvae already in the wood will continue feeding through winter. Find a certified arborist near you who specializes in pest management and tree health assessment.

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Stay ahead of seasonal threats all year long with TreeIssues' seasonal forecast, updated monthly for your region.