Basidiospores ofPucciniastrum goeppertianum(Kühn) Kleb. are globose, 5.8 μ in diameter, smooth-walled, apiculate, and have granular contents. The cardinal temperatures for their discharge were found to be 10, 18 to 20, and 25 °C. Development of new brooms from infected blueberry rhizomes started late in May, but shoots tested monthly in the laboratory released spores only from the next January until mid-June. The natural overwintering requirements of the fungus were mimicked by storing broom material at −4 °C from December until February.On balsam fir needles at 15 °C, germination of basidiospores usually produced a single, short germ tube, and exceeded 40% after 7 h of saturation and reached 70% by 48 h. Repetitive germination, commonly seen on glass slides or water agar, may only be typical of the reaction on non-host substrates. Only current-year needles were susceptible to infection and only from bud break until early in the 5th week, (corresponding approximately to the period of shoot elongation) provided that a minimum of 6 h at 15 °C under conditions of saturation preceded any period of drying of the foliage surface.