Asian Longhorned Beetle in September: Protect Your Trees Now

September is here, and for homeowners with hardwood trees, that means one of the most destructive wood-boring insects in North America is still very much on the move. The Asian Longhorned Beetle (ALB) — identified by USDA APHIS as a significant pest threat — is entering the final stretch of its typical activity window this month, making right now a critical time to inspect your trees and take action.

Check our seasonal forecast to stay current on what threats are peaking in your area.

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Why September Matters for This Threat

Based on typical timing, Asian Longhorned Beetle activity runs from May through September, placing this month at the tail end — but far from harmless — of its annual cycle. Adults that emerged over the summer have been feeding, mating, and laying eggs throughout the season. Larvae that hatched earlier are now tunneling deeper into trunks and branches, causing structural damage that may not become fully visible until next year.

Acting in September matters because:

• Adults may still be active, giving you a window to spot them and apply targeted treatments before they disappear for the season.
• Egg sites laid this summer can be identified and removed before larvae burrow further into wood.
• Early intervention now reduces the scale of infestation you'll face next spring.

Missing this window means damage accumulates unseen over winter, often leaving trees significantly weakened — or beyond saving — by the following season.

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What to Look for Right Now

The Asian Longhorned Beetle is a wood-boring insect that damages hardwood trees by tunneling deep into trunks and branches. Knowing the physical signs to look for is your first line of defense.

When inspecting your trees this month, pay close attention to:

• Round exit holes in bark, roughly the size of a dime, where adult beetles have emerged
• Shallow, oval or round egg-laying sites (oviposition pits) gouged into bark
• Sawdust-like frass (wood shavings mixed with excrement) collecting at the base of the tree or in branch crevices
• Visible adult beetles — they are large, black with white spots, and have distinctive long, banded antennae
• Dying or dead branches in the upper canopy, sometimes called "flagging"
• Weeping sap or staining on the bark surface near wound sites

Not sure what you're seeing? Use our diagnosis tool to help identify symptoms and get guidance on next steps.

For a complete description of this pest, visit the full details page.

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Where It's Active

This threat is currently tracked as MODERATE severity and is active across all 50 states, including Alabama, Alaska, Arizona, California, Connecticut, Florida, Georgia, Illinois, Massachusetts, Michigan, New York, Ohio, Pennsylvania, Texas, Washington, and every state in between.

Whether you're in the Northeast, the Pacific Coast, the Deep South, or the Mountain West, this is not a pest to dismiss as a regional concern. Hardwood trees — including maple, elm, willow, birch, poplar, and others — are at risk wherever they grow.

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What to Do This Month

September offers a meaningful opportunity to intervene. Here are the recommended actions for homeowners right now:

1. Targeted Insecticide Application If adult beetles are still present or you have a confirmed infestation, applying an appropriate insecticide can be effective. Timing is critical — treatments are most effective during active adult emergence and larval stages. Always follow label directions carefully, or consult a professional to ensure proper product selection and application.

2. Remove and Destroy Infested Material Prune any branches showing signs of boring activity, exit holes, or dieback. Remove fallen limbs and debris from around the base of affected trees. Do not move infested wood off your property without proper disposal — transporting infested material spreads the beetle to new areas. Chip, burn (where permitted), or bag and dispose of material away from healthy trees.

3. Explore Biological Control Options For those interested in lower-chemical approaches, biological control agents such as parasitic wasps and predatory beetles are options that can be introduced or encouraged. Ask a certified arborist whether these approaches are suitable for your specific situation and region.

4. Document What You Find Photograph any suspected signs and report confirmed or suspected Asian Longhorned Beetle activity to your state's department of agriculture or USDA APHIS. Early reporting helps slow the spread.

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When to Call an Arborist

Some situations go beyond DIY management. Contact a certified arborist immediately if:

• You find multiple exit holes or evidence of widespread tunneling across one or more trees
• A large or mature hardwood is showing canopy dieback or structural weakness
• You are unsure of the identification and need a professional assessment
• You want insecticide treatments applied safely and effectively
• A tree may need removal to prevent spread to neighboring trees

Don't wait until spring to make the call. Damage caused this fall and winter will compound quickly. Find a certified arborist near you who can assess your trees and recommend a treatment plan before the season closes.

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Stay ahead of seasonal threats all year long with TreeIssues.com's seasonal forecast. Early awareness is your most powerful tool.