Received for publication March 19, 1974. Michigan Agricultural Experiment Station Journal Article No. 6746. Research supported in part by a grant from the Netherlands Flower-bulb Institute, New York, and the Ornamental Marketing Board, The Hague. The authors acknowledge the assistance of Mr. W. S. McAfee of the Pesticide Center with the scanning electron microscopy and Dr’s. H. P. Rasmussen and J. Gogue of the Department of Horticulture with sample preparation.
Present address: Department of Ornamental Horticulture, The Hebrew University, Rehovot, Israel.