Received for publication 21 Feb. 1984. Journal paper no. J-11353 of the Iowa Agr. and Home Econ. Expt. Sta. Ames; Project 2231. The Iowa Turfgrass Institute is acknowledged for partial funding of this study. 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.