Asian Longhorned Beetle in September: Act Before the Season Ends

September marks a critical window for one of North America's most destructive wood-boring insects. The Asian Longhorned Beetle (ALB) — identified by USDA APHIS as a significant pest threat — typically remains active through May into September, meaning this month may represent your last reliable opportunity this season to detect damage, take action, and protect your hardwood trees before activity winds down. Don't let the calendar lull you into waiting until next year.

Check our seasonal forecast for the latest updates on pest pressure in your region.

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Why September Matters for This Threat

Based on typical activity patterns, Asian Longhorned Beetle adults and larvae are active from May through September. That makes late summer and early fall a pivotal time — adults that emerged earlier in the season have been feeding, mating, and laying eggs throughout the warm months. Any eggs deposited in July or August are now developing into larvae that will tunnel deeper into wood as temperatures cool.

Acting in September gives you the advantage of catching late-season adult activity while damage is still visible and accessible. Once cold weather sets in, larvae burrow further into heartwood where they are far harder to reach and treat. Timing, quite simply, is everything with this pest.

For the full scientific profile of this insect, visit our full details page.

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What to Look For Right Now

Asian Longhorned Beetle earns its name honestly — adults are large, striking insects with long antennae banded in black and white, and a glossy black body with white spots. But by the time you see the adult beetle, damage is already underway. Here's what to examine on your trees this month:

• Exit holes — Round, perfectly circular holes (roughly 3/8 to 1/2 inch in diameter) bored into bark are a hallmark sign of emerging adults.
• Sawdust-like frass — Look for coarse, fibrous sawdust accumulating at the base of the tree or in branch crotches, pushed out by tunneling larvae.
• Egg-laying sites — Female beetles chew shallow, oval depressions in bark before depositing eggs. These wounds may weep sap or appear discolored.
• Structural damage — Branches with unexplained dieback, canopy thinning, or limbs that have broken under normal conditions can indicate extensive internal tunneling.
• The beetles themselves — Adults are most active on warm, sunny days. Check tree trunks and branches carefully.

Unsure what you're looking at? Use our diagnosis tool to upload photos and get guidance.

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Where It's Active

This season, Asian Longhorned Beetle has been tracked across a wide geographic range — from the Northeast to the Deep South, the Pacific Coast, the Mountain West, and the Midwest. Essentially, if you have hardwood trees, you are in a region where this pest has been documented as active this year. Maples, elms, willows, birches, poplars, and other hardwoods are among the tree types known to be vulnerable to this insect's tunneling damage.

No matter where you live in the continental United States — or in Hawaii or Alaska — staying vigilant this September is worthwhile.

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What to Do This Month

With the activity window closing, now is the time for decisive action. Here are the recommended management approaches:

1. Targeted Insecticide Application Applying an appropriate insecticide now — during the late adult emergence and egg-laying stage — can interrupt the pest's life cycle before larvae establish deep tunnels. Always follow product label directions exactly, and prioritize timing around the vulnerable stages. A licensed arborist or pest management professional can help you select the right product and method for your specific trees.

2. Biological Control Agents For those preferring reduced-chemical approaches, natural predators and parasitoids play a role in managing beetle populations. Encouraging or introducing predatory beetles and parasitic wasps can provide supplemental pressure. Discuss options with a professional to understand what's appropriate and available in your area.

3. Infested Material Removal If you've confirmed damage or infestation, prune and destroy affected branches promptly. Remove any fallen debris from around the base of trees — wood chips, branches, and bark can harbor eggs and young larvae. Critically, do not move infested wood off your property without checking local regulations, as this can spread the beetle to new areas.

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When to Call an Arborist

Asian Longhorned Beetle is a federally recognized pest threat, and confirmed infestations are subject to regulatory reporting in many states. You should contact a certified arborist or your local USDA APHIS office immediately if:

• You find circular exit holes or the beetles themselves on your trees
• You observe significant unexplained canopy dieback in hardwood trees
• You're unsure whether what you're seeing is ALB damage or something else
• You want professional insecticide treatment applied safely and at the right time

An ISA Certified Arborist can assess your trees, confirm identification, coordinate with regulatory authorities if required, and develop a treatment plan before this season's window closes entirely.

Find a certified arborist near you — don't wait until spring to make that call.

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Asian Longhorned Beetle activity timing described in this article reflects typical seasonal patterns and may vary by location and year. Always consult local extension services or a certified arborist for region-specific guidance.