This is a classic example of earth-wood contact leading to deterioration and insect activity that I discovered at a recent home inspection in Friday Harbor on San Juan Island.  Pictured here is a deck baluster and pressure-treated stair stringer, both of which are deteriorated where they are in contact with the ground.  Elevated moisture conditions lead to WDO (wood destroying organism) activity, e.g., carpenter ants, anobiid beetles, termites, rot fungus, etc.  I always recommend keeping all exterior elements clear and free of the ground and landscaping elements to help prevent insect and water damage.