Received for publication May 2, 1979. Vermont Agricultural Experiment Station Journal Article No. 421. We thank Dr. N. E. Pellett for his assistance in the preparation of the manuscript. This study was supported in part by a grant from the Horticultural Research Institute, Washington, D. C.
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.
Present address: Department of Horticulture, Coastal Plain Experiment Station, Tifton, GA 31794.
Present address: Department of Plant Pathology, Fernold Hall, University of Massachusetts, Amherst, MA 01002.