Turfgrasses, as invaders of other turfgrasses, provide interesting examples of competitive mechanisms and possible methods for selective control. This knowledge may help craft management systems for turfgrasses as invaders of natural areas, as well as provide more uniform, utilitarian turf surfaces. The matrix of possible turfgrass mixtures contains a few combinations that are most commonly problematic. Several herbicides, e.g., those in the sulfonylurea chemical family, can selectively remove one turfgrass species from another. Cultural methods such as mowing height are also useful in shifting mixtures towards a monoculture. Characteristics of turfgrasses as turfgrass invaders parallels to some degree their potential for invasion into natural areas, due to rhizomes (e.g., bermudagrass, Cynodon spp., and kikuyugrass, Pennisetum clandestinum) and their reproduction by seed (annual bluegrass, Poa annua, and bahiagrass, Paspalum notatum). Underground physical barriers can isolate highly rhizomatous species such as zoysiagrasses, Zoysia spp. The potential invasiveness and sensitivity to invasion of turfgrasses can be further predicted by considering the openness of canopy and other stand characteristics such as height and growth habit, and the ability to grow in shaded environments. Turfgrass invasion of turfgrass can be reduced by the use of clean planting sources. When two turfgrass species reproduce at the seed source, seed contamination and subsequent distribution as "other crop seed" can occur, e.g., bentgrass, Agrostis sp. invasion of fescue species, Festuca spp. Such seed contamination may also be an indirect source of problem for natural areas. The competitive ability of turfgrasses is important in the maintenance of uniform turf stands, but turfgrasses are weeds, when they invade other turfgrasses or natural areas. The photograph shows St. Augustinegrass, Stenotaphrum secundatum, invading a golf course tee composed of a mixture of bermudagrass overseeded with roughstalk bluegrass, Poa trivialis.