Received for publication 17 Apr. 1985. Cooperative investigation of the Univ. of Maryland Agricultural Experiment Station and the ARS/USDA Service Experiment Station Scientific Article No. A-4054, Contribution No. 7039 of the Maryland Agricultural Experiment Station. We express our appreciation to Chesapeake Nurseries in Salisbury, Md., for providing ground beds and azaleas for this research. Technical assistance by Barbara Abbott, Pat Bagley, Annemarie Edwards, Teresa Rice, and Paul Roberts is greatly appreciated. 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.