The role of weather and topography in the development of Dothistroma septosporum.

Dothistroma septosporum (Dorog.) Morelet is recognized worldwide as a foliar disease of pine trees, infecting needles and causing premature defoliation. This results in reduced growth of the tree and, in severe cases, death. Red banding, caused by the mycotoxin dothistromin, along needles where infection has been successful characterizes this fungal pathogen. Symptoms develop sooner with higher temperatures and longer wetness periods. In a severe outbreak of Dothistroma needle blight in the Skeena Stikine Forest District in northwestern British Columbia (BC), damage has ranged from low levels of infection to nearly 100% mortality. A high concentration of young susceptible hosts and warm, moist summers and cool, wet falls in this area are thought to be contributing to the outbreak. Heavy fogs that persist in plantations close to rivers, lakes, or streams may also facilitate D. septosporum development. The purpose of this research is to identify climatic and site conditions contributing to the development of Dothistroma needle blight with respect to the severe outbreak happening in northwestern BC. The main objectives are to monitor the variation in disease expression, identify the ranges of temperature and humidity conducive to disease development, and identify site factors associated with disease. In the Skeena Stikine Forest District four sites were selected according to signs of Dothistroma infection, accessibility, and the presence of trees within 10-25 years of age. Within each site, three plots were established for weekly monitoring. In each of the twelve plots, weather stations were set up and six trees were selected. Six plots also had leaf wetness sensors. On each tree, four cohorts of ten needles were marked. These needles were examined weekly for the development of red bands, fruiting bodies, and spore production. When fruiting bodies were detected, needles were extracted from the tree for dissection to determine their reproductive state. Survey data of lodgepole pine plantations in the Skeena Stikine