Assistant Professor. Present address: Texas Agr. Res. and Extension Center, 2415 East Hwy. 83, Weslaco, TX 78596.
Received for publication 23 April 1984. Journal article no. 13,913 of the Minnesota Agr. Expt. Sta. Financial assistance provided by the Governor’s Council for Rural Development. 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.