Ontario’s beech trees are slowly being consumed by a disease that’s been on a steady march through the province for decades, experts say. Beech bark disease comes as a two-part attack. First, a small insect burrows into the tree. Then a fungus takes over, slowly rotting the tree and causing it to die. ​”After the insect has moved through, then the fungus will follow and cause the cankers on the tree,” said Sylvia Greifenhagen, a research forester with Ministry of Natural Resources and Forestry. “When you get enough of these killing cankers in the bark, the tree will die.” The disease has been relatively slow moving, arriving in Canada in the 1890s and gradually spreading through the Maritimes, Quebec and now Ontario. Greifenhagen said the ministry has research plots across the province to track the disease’s movement. In some cases, it’s already taken a considerable number of trees.