Risk from Sirococcus conigenus to understory red pine seedlings in northern Wisconsin

Interest in development of multicohort stands of red pine (Pinus resinosa) in the Great Lakes region of North America prompted an investigation of the potential impact of the shoot blight pathogen Sirococcus conigenus (syn. S. strobilinus) on understory red pine seedlings. In May 2002 and 2003 healthy, 1‐year‐old red pine seedlings were planted in the understory of a maturing red pine plantation in northern Wisconsin in an area with a history of presence of this pathogen. Occurrence of shoot blight symptoms was recorded periodically during the summer, and in each year seedlings were harvested in fall and examined for signs of shoot blight pathogens. By fall 2002 and 2003, respectively, shoot blight incidence was 89% and 98% and most seedlings were dying. Pycnidia with conidia of S. conigenus were present on almost all of the symptomatic seedlings. The conifer shoot blight and canker pathogen Diplodia pinea (syn. Sphaeropsis sapinea) was also detected, though less frequently. Pycnidia of S. conigenus tended to be found more frequently on symptomatic current year's shoots than symptomatic previous year's shoots; the opposite was true for pycnidia of D. pinea. Risk from S. conigenus to understory red pine seedlings should be considered in any plans for development of multicohort red pine stands in areas where the pathogen is present.