Cedar wood has a natural defense mechanism in the wood to keep bugs at bay, however, if the wood is old and damaged it will find it’s way to the new food supply. Pressure treated pine wood for fences has a chemical added to the wood to ward off insects and bugs. When the wood dries out and is not either stained or painted this is when an old wood fence will start to deteriorate. This too is a great new resource for food supply for bugs and insects!
Lastly another culprit for fence post damage is water. Water is not a friend to wood. When water is added to the wood it plumps up and then dries out and just erodes the wood surface over time. Ever seen a piece of driftwood floating in the water? When it comes to shore it is not a sturdy strong piece of wood anymore. Water damages fences when the fence post was not installed properly.
The fence post should have concrete as a base that surrounds the wood below ground. When concrete is not used the standing fence will be very short lived. All wood fence posts should be set in concrete period. This helps deter the rotting process. However if the concrete and fence post was not set right, water can build up at the base of the fence post. Over time the wood post will begin to rot, get weak and lean or fall down.