Protecting Log Railings from Carpenter Bees & Pests

Softwoods like pine, cedar, and spruce are the foundational materials for rustic railings. They are beautiful, easy to work with, and tragically delicious to a wide variety of wood-boring insects.

If left unprotected, a perfectly solid log post can be hollowed out into a fragile honeycomb within just a few seasons. The key to preserving your investment is identifying the specific pest attacking your wood and applying the correct localized treatment.

This guide covers the three most common enemies of exterior log structures and how to defeat them.

1. The Heavy Bomber: Carpenter Bees

Carpenter bees are the most visible and aggressive threat to raw log railings. They look precisely like large bumblebees but feature a shiny, hairless black abdomen.

Unlike termites, carpenter bees do not eat the wood. The females bore perfectly round, half-inch holes straight into the sides of logs or the unsealed underside of bottom rails to excavate breeding galleries. They prefer soft, unpainted, or weathering wood.

How to Identify an Attack

• You will see the bees hovering aggressively around the fascia boards, top rails, and posts of your deck in early spring.
• You will find perfect, half-inch circular holes drilled horizontally into the wood, often turning 90 degrees immediately inside to run parallel with the grain.
• Look for piles of coarse sawdust (frass) accumulating directly beneath the entry holes on the deck floor or ground.
• Look for yellow/brown fecal stains radiating downward from the hole entry.

Prevention and Treatment

1. Seal the Wood: Paint, heavy varnish, or thick synthetic stains offer the best deterrence. Penetrating oil stains (common on log homes) are less effective at stopping them but far better than bare wood.
2. Apply Citrus Sprays: Carpenter bees hate the smell of citrus oil. Spraying specialized citrus deterrents around the eaves and common nesting areas in early spring can discourage them from landing.
3. Active Extermination: Treat active nests forcefully. Wait until dusk when the bees are inactive inside the gallery. Spray a specialized foaming insecticidal dust (like DeltaDust or Drione) directly into the hole. The foam expands to coat the entire gallery and kills the adults and any hatching larvae over several months.
4. Plug the Holes: Wait 48 hours after dusting. You must permanently seal the hole to prevent a new generation from returning the following year. Tap a half-inch wooden dowel coated in waterproof wood glue deep into the hole, cut it flush with a saw, and seal over it with exterior wood putty.

2. The Silent Destroyer: Powderpost Beetles

Powderpost beetles are far more insidious than carpenter bees. They are tiny (less than a quarter-inch long), incredibly destructive, and almost entirely invisible until severe damage has occurred.

They attack the starchy sapwood of hardwoods (like hickory rails) and occasionally softwoods (like pine). The adults lay eggs in the microscopic pores of the wood. The larvae hatch and spend up to five years deep inside the log, turning the solid interior into a fine, flour-like powder.

How to Identify an Attack

• You will not see the insects.
• You will discover dozens of tiny “exit holes” (ranging from the size of a pinhead to a pencil lead) clustered tightly together on the surface of the log.
• If you gently tap the log near these holes, a cascade of incredibly fine, talcum-powder-like dust will fall out.

Prevention and Treatment

Once a powderpost beetle infestation is confirmed, surface sprays are useless because the larvae are buried inches deep in the wood.

1. Kiln-Dried Lumber: The absolute best prevention is ensuring the logs you buy for your railing were properly kiln-dried at high temperatures, which kills all eggs and larvae before installation.
2. Borate Penetrating Treatments: Borate (Tim-bor or Bora-Care) is a water-soluble mineral salt that is highly toxic to insects but safe for mammals. Mix the powder with water and spray or brush it heavily onto bare, unsealed wood. It penetrates deep into the log fibers via capillary action, poisoning the wood source permanently. This only works on raw wood; it cannot penetrate existing stain or varnish.

3. The Ground Threat: Subterranean Termites

Termites live in massive underground colonies and require constant contact with moist soil. They travel up into wood structures through mud tubes built along foundation walls or posts.

Prevention for Railings

The most critical rule for log railing installation is maintaining clearance.

A log newel post should never, under any circumstances, be buried directly in the soil or allowed to touch damp garden mulch. Ensure your deck framing and posts sit atop concrete footings or specialized metal standoff anchors that elevate the wood base at least one inch above the deck surface to prevent water pooling and cut off easy ground access for termites.