Professor and Head of Agronomy (formerly Professor of Horticulture).
Received for publication 2 Sept. 1988. Published as Paper no. 8723 Journal Series, Agricultural Research Division, Univ. of Nebraska, Lincoln. This research was supported in part by funds from the U.S. Golf Assn, and the Nebraska Turfgrass Foundation. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate this fact.