Asian Longhorned Beetle in September: Protect Your Hardwoods Now

September is here, and if you have hardwood trees on your property, this month deserves your full attention. The Asian Longhorned Beetle (ALB) — identified by USDA APHIS as a significant pest threat — is approaching the final stretch of its typical activity window, which runs from May through September. That means right now, adults may still be active, eggs laid earlier in the season are hatching, and larvae are tunneling deeper into your trees before temperatures drop. Acting this month could mean the difference between saving a tree and losing it.

Check our seasonal forecast for what's coming next in your region, and see the full details on this pest for a deeper dive into its biology and behavior.

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Why September Matters for This Threat

Based on typical timing, the Asian Longhorned Beetle's activity window spans May through September. That makes this month the closing chapter of peak season — but don't let that lull you into complacency. Late-season adults are still capable of laying eggs in bark, and larvae that hatched from summer egg masses are now actively feeding and burrowing into heartwood. The internal damage happening right now, largely invisible from the outside, can compromise a tree's structural integrity and long-term health well into next year. Early detection in September gives homeowners and arborists the best chance to intervene before larvae overwinter deep inside the wood.

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What to Look for Right Now

The Asian Longhorned Beetle is a wood-borer, meaning much of its damage occurs beneath the bark where it's hard to see. That said, there are visible warning signs to watch for during your September inspection:

• Round exit holes in the bark, roughly the size of a dime, where adult beetles have emerged
• Sawdust-like frass (a mixture of wood shavings and insect waste) accumulating at the base of the tree or in bark crevices
• Weeping sap or staining on the trunk and major branches
• Chewed or notched bark where adult beetles have fed on young branches
• Yellowing, wilting, or dropping leaves earlier than expected for the season — a sign of internal stress
• Egg sites: shallow, oval depressions in the bark where females have chewed down to lay eggs

If you're unsure what you're seeing, use our diagnosis tool to help identify the issue from photos and symptoms.

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Where It's Active

This pest is currently tracked as active across all 50 states, making it a nationwide concern for anyone with hardwood trees on their property. Susceptible species include maple, elm, willow, birch, poplar, ash, and several others. Whether you're in the Northeast, the Deep South, the Pacific Northwest, or anywhere in between, your hardwoods are potentially at risk during this activity window.

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What to Do This Month

With the season winding down but not over, September is a critical window for action. Here are the evidence-backed steps to take right now:

1. Targeted Insecticide Application If adult beetles have been confirmed on or near your property, applying an appropriate insecticide can reduce populations and protect vulnerable trees. Timing is critical — treatments are most effective during the adult emergence and activity stage, which is right now. Always follow label directions carefully, and consider consulting a professional for application near large or mature trees.

2. Infested Material Removal If you've identified infested branches or sections of bark, prune and destroy that material immediately. Remove any fallen debris, bark, or wood chips from beneath affected trees, as these can harbor eggs or early-stage larvae. Do not move infested wood to another location — dispose of it away from healthy trees and in accordance with any local regulations on ALB-infested material.

3. Encourage Biological Controls Natural predators and parasitoids can play a supporting role in managing beetle populations over time. Encouraging habitat for parasitic wasps and predatory insects in your landscape is a low-risk, long-term strategy that complements direct treatments.

4. Document and Monitor Take photos of any exit holes, frass, or egg sites you find. Record which trees are affected and how extensively. This documentation is invaluable when working with an arborist or reporting to local agricultural authorities.

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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 widespread frass on a single tree
• A large or mature hardwood is showing crown dieback or early leaf drop
• You're unsure whether the damage is from ALB or another pest
• You need help with insecticide selection, timing, or safe application
• A tree appears structurally compromised and may pose a safety risk

The Asian Longhorned Beetle is a federally recognized pest threat, and in some areas, infestations must be reported to USDA APHIS or your state department of agriculture. A qualified arborist can help you navigate both the treatment and the reporting process.

Find a certified arborist near you to get a professional assessment before the season closes out.

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September is your last reliable opportunity this season to catch active adults and address new egg masses before they become next year's problem. Walk your property this week, know what to look for, and don't wait. Your hardwood trees are worth protecting.