Environmental factors affecting Sirococcus shoot blight of black spruce

Abstract

Pathogenic isolates of Sirococcusstrobilimts from Piceamariana were studied under laboratory conditions to determine the temperature, light, and humidity requirements for conidial germination, mycelial growth, pycnidial production, and infection of spruce seedlings. Conidial germination and mycelial growth occurred between 5 and 30 °C. The fungus survived temperatures of −10 °C, as well as outdoor winter conditions, for several weeks. Temperatures of 35 °C were lethal to spores and mycelium after exposure of 2 and 7 days, respectively. Light did not measurably affect conidial germination and mycelial growth but was necessary for pycnidial production. Infection of Piceamariana seedlings occurred in artificially inoculated seedlings enclosed in plastic bags to maintain a high humidity for at least 1 day after inoculation. Infection was greatest under a daily temperature cycle of 16–21 °C, less at 10–16 °C, and significantly reduced at 24–30 °C. At all temperature ranges, the percentage infection was greater under low light intensities (900–3900 lx) than under relatively high light intensities (4300 – 10 000 lx). It is concluded that warm sunny weather during the period of susceptibility would probably control this desease; protective measures are necessary only if frequent or prolonged periods of below-average temperatures and wet cloudy weather occur during the summer months.