Received for publication 4 Aug. 1983. Scientific Paper No. 6607, Project 0198, Washington State University College of Agriculture Research Center. Pullman, WA 99164. This research was supported in part by a grant from the Washington Tree Fruit Research Commission. 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.