Asian Longhorned Beetle Is Still Active — Here's What Homeowners Should Do This September

If you have maples, elms, willows, or other hardwoods on your property, September deserves your full attention. The Asian Longhorned Beetle (ALB) — identified by USDA APHIS as a significant pest threat — is wrapping up what is typically its most active stretch of the year, and the damage it leaves behind can quietly set the stage for serious tree decline heading into winter.

Check our seasonal forecast to see what other threats may be converging on your landscape this fall.

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Why September Matters for This Threat

Based on typical patterns, the Asian Longhorned Beetle's activity window runs from May through September. That makes this month the closing chapter of peak season — but closing doesn't mean over. Adult beetles may still be present, and larvae that hatched earlier in the summer are now tunneling deeper into wood, feeding aggressively before winter sets in.

This late-season activity is particularly damaging because larvae burrowing through heartwood and sapwood disrupt a tree's vascular system at a critical time — just as the tree is moving nutrients into storage for winter. Trees weakened by ALB tunneling enter the cold months already compromised.

September is also when fresh exit holes and sawdust-like frass become easier to spot, as summer foliage begins to thin. That visibility window matters: the sooner you detect an infestation, the more options you have. Get the full details on this pest to understand its full lifecycle and risk profile.

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What to Look For Right Now

ALB is a wood-boring insect, which means the most telling signs are structural — look at the tree itself, not just the leaves. Walk around each hardwood on your property and examine:

• Round exit holes in the bark, roughly the size of a dime, with perfectly circular edges (not ragged like woodpecker damage)
• Sawdust-like frass accumulating at the base of the tree or in branch crotches — this is a byproduct of larval tunneling
• Oozing sap or weeping wounds on the trunk or major branches
• Adult beetles, if still present: they are large (1–1.5 inches), glossy black with white spots, and have distinctive long, banded antennae
• Yellowing or wilting branches in the upper canopy that seem out of step with normal fall color change

Unsure what you're seeing? Use the TreeIssues diagnosis tool to walk through your observations and get guidance on next steps.

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Where It's Active

This threat is currently being tracked across all 50 states, meaning no region of the country is categorically off the hook. Hardwood-dense landscapes in the Northeast, Midwest, and South face elevated concern, but the USDA APHIS designation as a pest threat reflects a nationwide scope. If you have hardwood trees — maples, birches, elms, horse chestnuts, willows, and others — you should be conducting a visual inspection this month regardless of where you live.

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What to Do This Month

September action can make a meaningful difference. Here are the three treatment approaches relevant to ALB:

1. Targeted Insecticide Application If adult beetles are still active in your area, timing is everything. Insecticides are most effective when applied during vulnerable adult emergence or early larval stages. Follow all label directions carefully, and consider consulting a professional to identify the right product and application window for your region.

2. Remove Infested Material Prune out any branches showing clear signs of infestation — exit holes, heavy frass, or structural decline. Do not leave cut material on-site. Remove and dispose of it well away from healthy trees. Fallen debris, including bark and branch wood, can harbor eggs or young larvae and should be cleared from around the base of trees.

3. Biological Control Agents For those managing larger properties or looking for integrated approaches, natural enemies of ALB — including parasitic wasps and predatory insects — can play a supporting role. Discuss biological control options with a licensed arborist or extension specialist before introducing any agents.

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When to Call an Arborist

DIY inspection is valuable, but Asian Longhorned Beetle is a federally recognized pest threat for a reason. Call a certified arborist immediately if:

• You find multiple exit holes on a single tree
• You suspect infestation in a large or mature specimen that provides shade, structure, or significant property value
• You're uncertain whether what you're seeing is ALB damage or something else
• A neighbor's tree has been confirmed infested

In some states, confirmed ALB infestations trigger regulatory response, including mandatory removal. An arborist can help you navigate that process and document the damage properly.

Find a certified arborist in your area through the TreeIssues directory and schedule an inspection before the end of the month while conditions still allow for a thorough assessment.

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Don't wait for spring to address what's happening in your trees right now. September is a narrow but important window — use it.