Phomopsis and Sirococcus Shoot Blights of Colorado Blue Spruce in Wisconsin. P. G. Sanderson, Department of Plant Pathology, University of Wisconsin, Madison 53706. G. L. Worf, Department of Plant Pathology, University of Wisconsin, Madison 53706. Plant Dis. 70:1159. Accepted for publication 24 July 1986. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/PD-70-1159b.
Needle necrosis and tip blight on 3–0 Colorado blue spruce in a Wisconsin nursery were caused by Phomopsis occulta Trav., a fungus previously regarded as only saprophytic on this host (1). Initial symptoms were chlorotic flecks on the basal half of needles near the shoot tips, followed by small stem cankers and often accompanied by resinous exudates. Symptom severity was greatest when inoculated plants were maintained at a warm temperature (25 vs. 16 C) and high relative humidities (79–95 vs. 25–36%). Picea pungens Engelm., P. obovata Ledeb., P. glauca (Moench) Voss ‘Densata,’ P. abies (L.) Karst., Abies balsamea (L.) Mill., and A. concolor (Gord.) Lindl. were inoculated with P. occulta. Only spruce species, particularly P. pungens, showed symptoms. Sirococcus strobilinus Preuss was isolated from a 15-yr Colorado blue spruce showing symptoms similar to those caused by P. occulta. Pathogenicity of S. strobilinus was confirmed for the first time on this host in Wisconsin.