Cyclaneusma Needlecast and Needle Retention in Scots Pine. W. Merrill, Professor, Penn State University, University Park 16802. N. G. Wenner, Senior Research Assistant, Department of Plant Pathology, Penn State University, University Park 16802. Plant Dis 80:294. Accepted for publication 30 November 1995. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-0294.

Portions of two Pennsylvania Pinus sylvestris Christmas tree plantations, each of a different provenance, were left untreated or treated repeatedly with fungicide to prevent infection of the 1990, 1991, and 1992 needle complements by Cyclaneusma minus. Periodically from July 1990 to August 1992, incidence of infection by C. minus was determined by direct isolation from needles of the 1990 and 1991 complements of permanent sample trees within each treatment block. Treatment with fungicide significantly increased retention of third-year needles, but not of second-year needles of these provenances. Fungicide treatment also significantly increased the proportions of trees retaining more than 50% of their third-year needles. Retentions of third-year and second-year needles on individual trees were not correlated and varied greatly among individual trees regardless of infection by C. minus. Results indicate a host genetic factor independently affecting needle retention in Scots pine, upon which are superimposed the effects of Cyclaneusma needlecast, and which has confounded all previous evaluations of the impact of this disease