Kentucky bluegrass (Poa pratensis) is the backbone of the cool season turfgrass industry. In Arizona, it's equivalent to "high elevation" bermuda. It is used successfully in areas of 4000 foot elevation and greater. Kentucky bluegrass is originally from Europe and throughout the centuries different ecotypes have established themselves in the different climatic zones of the U.S. Most of the Kentucky bluegrass varieties have been developed at Rutger's University. There it was discovered how to hybridize Kentucky bluegrass. Most plants of Kentucky bluegrass are apomictic. This means they reproduce plants exactly like the mother plant, through seed. It is essentially asexual propagation, were all the seeds are essentially genetically alike. This is an advantage in that uniform turf varieties can be produced. The disadvantage is that it is hard to incorporate variation or new traits into plants which have other desirable turf characteristics. At Rutger's, a pollination scheme was devised (in 1970 or so) to incorporate new genes from apomictic plants into plants which reproduce truly by sexual means. The results yield new plants from seed which have characteristics of both parent plants and often reproduce them uniformly since the newly developed plant develops its seed through apomixis.

Many of the improved varieties of KBG have been developed with enhanced disease-resistance. The major diseases of KBG include the leaf spot/crown rot syndrome which occurs in the spring and is worse during cloudy weather. The other major diseases for KBG include the patch diseases (summer patch and necrotic ring spot). These are root diseases which show major expression during the summer months.

On the next page is a classification scheme of Kentucky bluegrass varieties which lists their growth characteristics. For Arizona, the Mid-west types are used for low maintenance KBG turfs. The aggressive types should be used for high maintenance sports fields and can be mixed with perennial ryegrass for re-seeding purposes.