Artificial Infection and Development of Snow Mold Fungus (Phacidium infestans) in Container-grown Norway Spruce Seedlings

Phacidium infestans causes common snow mold in Scots pine (Pinus sylvestris L.), its main host in Finland. Recently, a mycelial web similar to that occurring on pine has been observed on Norway spruce (Picea abies L.) seedlings in some forest nurseries of Finland. In this study, we showed that Ph. infestans can cause snow mold in container seedlings of Norway spruce exposed to treatments that simulated natural infection by ascospores borne on Scots pine saplings. In the following spring after infection, inoculated seedlings stored in the freezer (-3 degrees C) were generally more diseased than those stored outdoors during the 2006/2007 winter, suggesting that Ph. infestans does not require snow cover to develop on spruce seedlings. Diseased needles were grey-green in early spring. After death, diseased needles soon became yellow-brown or grey-brown and seedlings often died. In contrast to the disease in Scots pine of the same age, infected Norway spruce needles were dropped mainly during the summer of 2007. Although the final examination took place about two years after artificial infection, we did not observe any mature fruiting bodies of Ph. infestans on spruce or pine seedlings included in the experiment as a reference.