CYTOSPORA CANKER OF POPLARS: FACTORS INFLUENCING THE DEVELOPMENT OF THE DISEASE

Abstract

The effects of shoot moisture content, region of shoot, age of shoot, temperature, relative humidity, and soil moisture content on the development of cankers caused by Cytospora chrysosperma (Pers.) Fr. were studied in Populus trichocarpa Torr. and Gray, P. × canadensis Moench 'Regenerata', and P. × canadensis 'Robusta Bachelieri'. Within the range studied, canker growth varied proportionally with temperature, and inversely with shoot moisture content, relative humidity, and soil moisture content. Canker growth was greater in P. trichocarpa than in the two hybrids, which did not differ significantly from each other. Canker growth was less in 8-month-old than in 10- and 12-month-old shoots of the hybrids, but cankers on P. trichocarpa showed no differences in this respect. The critical bark moisture deficit for infection was least in P. trichocarpa, intermediate in P. 'Regenerata', and greatest in P. 'Robusta'. The critical bark moisture deficit was greater, and the incubation period was shorter, in the upper part than in the lower part of the shoot.