Annual Bluegrass (Poa annua) is a native of Europe and is found worldwide. "Poa", as most members refer to it, likes moist, shady sites and prefers rich, compacted soils. These conditions are typically found on older golf courses and greens like the South Course.
The South greens are original Donald Ross greens (except #'s 7,8,15,12) and are composed of organic soils amended by many years of topdressing with sand. The North Course greens were rebuilt by Robert Trent Jones in 1969, seeded with Penncross bentgrass, and have soils with a high percentage of sand. The North greens have good internal drainage.
Annual Bluegrass is a prolific seed producer and with the ability to survive in hostile environments, can quickly establish itself in greens, tees and fairways. A small plant can produce up to 100 seeds. These seeds can germinate rapidly and with the ability to survive under very close mowing heights, can overtake a green surface in a few years.
Once established, it is extremely difficult to control and still maintain quality putting surfaces. Some herbicides are available to eliminate annual bluegrass .... but with large areas of bare turf on putting greens, the superintendent is often eliminated as well and therefore we choose not to use herbicides.