Asian Longhorned Beetle Peak Activity: What to Do This September

If you have hardwood trees on your property, September deserves your full attention. The Asian Longhorned Beetle (ALB) — identified by USDA APHIS as a significant pest threat — is entering the tail end of its typical activity window this month, and the damage it causes can be severe and long-lasting. Understanding what to look for right now, and acting quickly, could make the difference between saving a tree and losing it.

Check our seasonal forecast to see what other threats are peaking in your area this month.

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Why September Matters for This Threat

Based on typical timing, the Asian Longhorned Beetle is generally active from May through September. That makes this month the final chapter of its seasonal window — but don't let that lull you into complacency. Adult beetles that emerged over the summer have had weeks to feed, mate, and deposit eggs into the bark of your trees. Larvae that hatched from those eggs are now tunneling deeper into trunks and branches, doing structural damage that won't be fully visible until much later.

Acting in September means you can still disrupt this cycle before larvae overwinter and resume feeding next spring. Timing is everything with this pest, and this month is your last reliable opportunity to intervene during the current season.

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What to Look for Right Now

The Asian Longhorned Beetle targets hardwood trees — think maples, elms, willows, birches, poplars, and related species. During a September inspection, walk slowly around your hardwoods and examine the trunk, major limbs, and branch unions carefully. Key signs associated with ALB activity include:

• Round exit holes in the bark, roughly the diameter of a dime, where adult beetles have emerged
• Sawdust-like frass (wood shavings and excrement) collecting at the base of the tree or in bark crevices
• Shallow oval or round scars on the bark surface where females have chewed sites to deposit eggs
• Dying or dead branches in the upper canopy, sometimes called "flagging," that appear prematurely
• Sap or resin weeping from bark wounds

If you're unsure what you're seeing, use our diagnosis tool to get a clearer picture, or review the full details on Asian Longhorned Beetle for a deeper look at this pest.

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Where It's Active

This threat is currently tracked as active across all 50 U.S. states. Whether you're in the Northeast, the Deep South, the Pacific Northwest, or the Mountain West, your hardwood trees are potentially within range this season. The USDA APHIS has flagged this beetle as a national pest concern, and no region should consider itself off the hook.

The severity level is currently rated moderate, but moderate doesn't mean minor — tunneling damage to a tree's vascular system is cumulative and can ultimately be fatal to the tree if infestations go unaddressed over multiple seasons.

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What to Do This Month

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

1. Targeted Insecticide Application If adult beetles or fresh signs of activity are present, applying an appropriate insecticide can help. Follow all label directions carefully. Timing matters — treatment aimed at adult beetles or newly hatching larvae is most effective. If you're not comfortable with chemical applications, this is a task best handed off to a licensed professional.

2. Remove Infested Material Prune and destroy any branches showing clear signs of infestation. Remove fallen limbs and debris from around the base of the tree, as this material can harbor eggs or larvae. Critically, do not move infested wood to other areas of your property or off-site without proper disposal — transporting infested material is one of the primary ways this beetle spreads to new locations.

3. Encourage or Introduce Biological Controls Natural predators and parasitoids can play a supporting role in managing ALB populations. Parasitic wasps and predatory beetles are among the biological control options that researchers and land managers have explored. Encouraging a healthy garden ecosystem that supports beneficial insects is a low-cost, long-term strategy worth pursuing.

4. Document and Report If you strongly suspect ALB activity, report it to your state department of agriculture or local USDA APHIS office. This pest is subject to regulatory oversight, and confirmed infestations may trigger official response efforts in your area.

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When to Call an Arborist

Call a certified arborist if:

• You find exit holes, frass, or egg-laying scars on your hardwoods and aren't sure how to proceed
• The affected tree is large, close to a structure, or would be dangerous to prune without professional equipment
• You want a proper diagnosis before committing to a treatment plan
• You've already attempted treatment and signs of activity persist

An ISA Certified Arborist can assess the true extent of internal damage — something that's impossible to gauge from the surface alone — and recommend a proportionate response. Use our find an arborist directory to locate a qualified professional near you.

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September won't last long. If you have hardwoods and haven't inspected them yet this season, this weekend is the right time to take a walk around your property and take a close look. Early action now protects your trees through winter and into next year.