Termites and Rot in West Tennessee Wood Fences

Look at the bottom of a failed fence post. In general, the ground line, where a post meets damp soil, is where decay and termites both tend to start. The Forest Products Laboratory notes that fences have at least some parts in soil contact, which is why decay and termite attack are potential problems.

In West Tennessee two things do that eating. Rot, which is fungus. And termites, which are insects. They can show up together, and homeowners mix them up all the time. The fix for each is a little different, so it helps to know which one you have.

I will stay inside what Tennessee's own extension service and the federal Forest Products Laboratory say, because they have tested this and I have not. Where you need a pest control company, I will say so, because we build fences and do not treat for bugs.

Why This Climate Is Hard on Wood

Jackson's climate is humid subtropical, and it gets a lot of rain. Damp wood in contact with soil is what decay and termites need, so the ground line is where to look.

The U.S. Forest Products Laboratory puts it directly in its publication on exterior wood in the South. For fences, it says, decay and termite attack are potential problems, and for maximum service life all wood fence posts used in the South should be pressure treated with a wood preservative. It also reports that preservative treatment can extend by tenfold the service life of nondurable wood in soil contact. In a test in southern Mississippi, untreated pine posts lasted only a few years while treated posts lasted decades. That is a Mississippi result, not a Tennessee one.

Local building paperwork points the same direction. Madison County's adopted design table rates termite risk as moderate to heavy. The City of Jackson's construction guide says termite protection is required and notes the area is subject to decay and weathering. Those are building rules for houses, not fence rules.

Is It Rot or Termites?

Look at the failed wood and compare.

• Rot is decay, and in general it leaves wood soft, spongy or crumbly, so a screwdriver pushes in with little effort. It tends to start where moisture sits, such as the ground line. This is a general rule of thumb, not something from the sources below.
• Termites are different. UT Extension says the workers eat the soft grain of the wood, leaving a thin shell outside and a layered effect inside, often with mud in the eaten layers. Look for mud tubes, which are covered passageways the termites build from bits of soil between the nest and the wood.
• Both can be present in the same post. Telling them apart by eye is not always easy, which is one more reason to bring in a pest professional when you see mud.

If you see mud tubes, stop and call a pest professional. University of Tennessee Extension's termite publication says securing the services of a reliable pest control professional is advisable in almost all cases, and a fence builder has nothing to add on treatment.

What UT Extension Says About Termites and Fences

The university calls subterranean termites the most destructive wood-feeding insects in Tennessee, and says they will also feed on fence posts. The colonies live in the soil. The workers are soft-bodied and need soil contact for moisture, so they build mud tubes as passageways from the nest to the food.

The same publication is written about houses and says nothing about fences. Applying its landscape advice where a fence meets a building is our inference.

• Wood or bark mulch placed against a foundation. UT says cellulose mulch there gives termites access to the home without crossing the soil treatment barrier.
• Wood landscape timbers and wood decks placed against the foundation or siding, which UT says can provide food and a way in.
• Plants and mulch right against the foundation. UT recommends a plant- and mulch-free zone next to the foundation, about a foot to a foot and a half wide.

It also notes that concrete or vinyl landscape borders do not provide food or access to termites the way wood does. Keep that in mind where a fence meets a bed or a house wall. More on plants and mulch near a fence is in our guide to hedges, vines and mulch near a fence.

What Slows Both Down

Pressure-treated wood in the ground

UT Extension says that for maximum protection, chemically treated lumber should be pressure treated with an approved preservative, and that brushing, spraying or soaking usually gives only limited protection. That advice is about house lumber. The Forest Products Laboratory says much the same: brushing, spraying or dipping only reaches a thin layer of the wood and will not last long in severe uses such as ground contact. A brush-on coat is a supplement, not a substitute. Tennessee 811 adds, in its own guidance, that any part of a post touching the ground should be pressure treated or be a decay-resistant species such as cedar.

Cut ends

Preservative maker Viance, citing the American Wood Protection Association standard for field treatment, says pressure treatment soaks into the sapwood but only a little reaches the heartwood, so cuts, drilled holes and other injuries that break through the treated zone need a preservative applied in the field, following the product label. Ask your contractor what they do at cut ends, especially on post tops and anything near the ground.

Keeping the ground line dry

As general practice, not from the sources above, posts last longer where water leaves. That means gravel under the post, grade that slopes away, and no mulch banked against the wood. Where a yard has a wet run, a different post material may be the better choice. The reasoning is in our guide to Madison County soils and fence posts.

Keeping plants off the wood

In general, vines and shrubs hold moisture against boards and hide problems until they are bad. Giving wood a little air is cheap insurance.

What Not to Do

• Do not pour a chemical on the ground around a post and call it treated. If termites are the problem, that is a job for a pest professional, not a fence crew and not a weekend project.
• Do not bury the base of a board in mulch or soil to hide the damage.
• Do not set a new wood post in the same wet hole without fixing what made the old one fail.
• Do not assume stain stops rot. A finish slows moisture on the surface. It does not replace pressure treatment in the ground.

Replace the Post, or Replace the Fence?

One failed post in a sound fence is a repair. A fence where several posts are soft at the ground line may be telling you the whole line has the same problem, and swapping one post only fixes that one. The way to decide is on our page about repairing or replacing a fence in Jackson. For the repair side, see fence repair services.

If you are building new and want wood, the wood fencing page covers species and treatment. The fence lifespan guide covers what to expect from each material here.

Questions to Ask Before You Buy a Wood Fence

You can learn a lot about a bid by asking how the contractor plans to keep the posts alive.

• Are the posts rated for ground contact, and what are they made of?
• What goes in the bottom of the hole, and how does water get out?
• What happens at cut ends and where boards meet rails?
• What are the nails or screws? The Forest Products Laboratory recommends hot-dipped galvanized, stainless or aluminum nails to avoid rust stains and blue-black discoloration under water-repellent finishes.
• How will the finished grade sit next to the boards, so mulch and soil are not piled on them?

A contractor who has real answers has thought about the ground line. One who shrugs has not. The rest of the list is in questions to ask a fence contractor.

Common Questions About Termites and Rot

The Short Version

Wood fences in the ground here fight rot and termites from the first day. Treated lumber, treated cut ends, and a dry ground line give the wood its best chance. If your fence is failing at the base, find out why before you replace it. Our Jackson fence installation page shows how we plan a build, and the Jackson fence repair page covers what a repair visit looks like.

More plain-English answers on cost, permits, materials, and repairs are in all of our fence guides.