Unfortunately, most do not. The ground is full of micro organisms that eat wood. Biodegradation is a cycle of life. The bacteria and fungi responsible for wood rot need four things to survive: Temperature(50°F-90°F), food, water, and oxygen. Wood rot generally does not occur more than a couple inches below grade. There is very little oxygen and the temperature is much colder. Wood Post rot occurs most commonly at the grade, where soil and air contact wood.
The Post Collar protects the post at the grade. In addition to preventing rot fungus, it can also protect against weed eaters, whackers, trimmers, mowers, tillers, and many other gardening machines. They are made of heavy-duty galvanized steel, not plastic.