Received for publication June 29, 1979. Paper No. 6259 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh. Cooperative investigations of the U. S. Department of Agricultural Science and Education Administration and the North Carolina State University. Mention of a trademark, proprietary product, or vendor does not constitute a guarantee or warranty by the U. S. Department of Agriculture or the North Carolina Agricultural Research Service and does not imply approval of it to the exclusion of other products or vendors that also may be suitable.
The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper must therefore be hereby marked advertisement solely to indicate this fact.
Professor, Department of Plant Pathology and Plant Pathologist, USDA-SEA-AR; and Professor, Department of Horticultural Science, respectively. The authors express gratitude to T. N. Gray and N. C. Mingis for their technical assistance; to Dr. J. O. Rawlings, Professor, Statistics Department, NCSU, for statistical assistance; and to Mikkelsens, Inc., Ashtabula, OH, for providing rooted cuttings used in this study.