The collar is a 24" wide strip of turf mowed around the green. Greens are mowed at .125" and Collars are mowed at .300". The collar is composed of Penn A4 bentgrass and is considered part of the green.
When you think about wear and tear on turf surfaces, one immediately thinks of the players themselves as the primary culprit. However, daily maintenance creates its own set of challenges. When we mow greens, we use "white boards" to turn the mower around on. I've used this practice for a number of years. It saves a lot of wear on our collars and intermediate rough around the green. It creates more work and adds a small amount of time to getting the greens cut but the results speak for themselves. Collars tend to be the most challenging surface to manage on a golf course for a number of reasons. The traffic from golfers and mowers always seems to be concentrated on collars. Increased traffic can lead to turf thinning and other forms of poor turf quality.