Cankers are diseases that attack the bark of trees.
Even the fungicides which are most toxic under lab conditions weren't effective in field trials on the Burnaby campus. As a result, Rahe says that emphasis should switch to cultural control. It's the windblown spore that is largely responsible for spreading the disease in an orchard and initiating the disease in previously healthy trees. The waterborne spore serves mainly to increase the number of cankers in a tree once it has been infected. Based on SFU research into the life cycle of the fungus, it's clear that winter pruning must include removal of all cankers.