Asian Longhorned Beetle: What to Do This September

September marks the final stretch of the Asian Longhorned Beetle's (ALB) typical activity window — and that makes this month a critical time to inspect your hardwood trees, act on what you find, and protect what you haven't yet lost. Identified by USDA APHIS as a significant pest threat, ALB damages hardwood trees by tunneling deep into trunks and branches, disrupting the vascular tissue trees depend on to move water and nutrients. Don't wait until leaves drop to investigate. Check our seasonal forecast to stay ahead of what's active in your area.

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Why September Matters for This Threat

Based on typical timing, Asian Longhorned Beetle is generally active from May through September. That means right now — as summer transitions to fall — you're at the tail end of the window when adult beetles are most likely to be visible, actively mating, and laying eggs in hardwood bark. This is also the period when larvae that hatched earlier in the season have been tunneling deeper into woody tissue, making damage increasingly difficult to reverse.

Acting in September gives you the best remaining opportunity to: - Spot adult beetles before they disappear for the season - Identify fresh egg sites and entry holes before they're obscured by bark - Remove and destroy infested material before larvae overwinter deeper inside the tree

If you're unsure what you're looking at, use our diagnosis tool for a quick guided assessment.

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What to Look for Right Now

Asian Longhorned Beetle leaves behind a distinctive set of clues. During your September inspection, walk slowly around each hardwood tree on your property and look for:

• Round exit holes roughly the size of a dime (approximately 3/8 to 1/2 inch in diameter) in the trunk or major branches — these are where adult beetles have emerged
• Egg-laying sites that appear as shallow, oval-shaped depressions or chewed patches in the bark
• Sawdust-like frass accumulating at the base of the tree or in branch crotches — a sign of active larval tunneling
• Adult beetles, which are large (up to 1.5 inches), shiny black with white spots, and have distinctively long black-and-white banded antennae
• Weeping sap or unusual staining on bark surfaces
• Yellowing, wilting, or dying branches — sometimes called "flagging" — in the canopy

See the full details on Asian Longhorned Beetle for a comprehensive description of this pest and its damage patterns.

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Where It's Active

This threat is currently being tracked across all 50 U.S. states, meaning no region should consider itself off the radar. Whether you're in a densely forested rural area or a suburban neighborhood with street maples and ornamental elms, hardwood trees anywhere in the country may be at risk during the active season. Urban and suburban trees are particularly vulnerable because they're often isolated, already stressed, and lack the biodiversity that can support natural checks on pest populations.

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What to Do This Month

If you find evidence of ALB — or want to take preventive action before the season closes — here are the recommended steps for September:

1. Remove and Destroy Infested Material If you identify infested branches, prune them out promptly. Remove fallen debris, bark fragments, and any wood that may harbor eggs or larvae. Do not move infested wood off your property without checking local regulations — transporting infested material can spread ALB to new areas. Chip, burn (where permitted), or bury the material on-site.

2. Apply Targeted Insecticide (If Appropriate) Insecticide treatments can be effective when timed correctly. September is a relevant window because some larvae are still in early, more vulnerable stages. Always follow label directions precisely, and select a product appropriate for wood-boring beetles. Timing and application method matter enormously — misapplication wastes product and may not reach the pest.

3. Encourage or Introduce Biological Controls For a lower-intervention approach, consider supporting conditions that attract natural predators and parasitoids. Parasitic wasps are among the biological control agents used against ALB in managed programs. While homeowner-level options here are limited, avoiding broad-spectrum pesticide applications can preserve beneficial insect populations.

4. Document and Report If you suspect ALB is present on your property, report your findings to your state department of agriculture or USDA APHIS. Early detection and reporting are among the most powerful tools available for limiting the spread of this pest.

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When to Call an Arborist

Not every situation is a DIY project — and Asian Longhorned Beetle is a case where professional eyes can make a real difference. Contact a certified arborist if:

• You've found suspected ALB damage but aren't certain of the identification
• Affected trees are large, mature, or structurally complex
• You need to safely remove substantial infested limbs or whole trees
• You want a professional insecticide injection or soil drench applied correctly
• You're concerned about liability or want documentation for insurance purposes

Find a certified arborist near you through our directory and schedule a fall inspection before the season ends. Acting now — while the pest is still in its active window and damage is still visible — gives your trees the best chance heading into winter.

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Stay informed all season long with our seasonal forecast and track emerging threats in your region before they catch you off guard.