Incidence of Septoria canker of hybrid poplars in eastern Ontario

Abstract

St?ptoria musiva is an endemic pathogen that causes leaf spots and cankers on hybrid poplar (Populus spp.) clones. Although canker incidence was lower in eastern Ontario, a 1984 study found little difference in the morphology and physiology of different isolates of S. musiva collected from plantations in the north central United States and those collected in eastern Ontario. By 1987, however, a high incidence of severe cankers in a few plantations was observed. A survey of canker incidence in all plantations (203 ha) of six exotic P. nigra x maximowiczii (NM) clones found that 7g0/o of the area was affected to some degree with Septoria damage. This represented 11% of the total area planted to hybrid poplar (1,450 ha) in eastern Ontario. Three things are speculated to have contributed to the increase in Septoria damage: (i) the area planted to susceptible NM clones had increased dramatically since 1981, (ii) the amount and type of secondary inoculum produced by the fungus in these exotic clones, rather than in the native poplar, may differ in aggressiveness and (iii) precipitation levels for the 1986 growing season were higher than normal. Five of the clones were determined to be too susceptible for further plantation establishment.