August 1, 2023
Sapwood staining is symptomatic of oak wilt.
Oak wilt confirmed in Canada
The Canadian Food Inspection Agency (CFIA) recently confirmed the first detected case of oak wilt in a residential area of Niagara Falls, Ont. The case is the first one to be confirmed in Canada.
Oak wilt is a serious vascular disease of oak trees caused by the fungus Bretziella fagacearum, which grows on the outer sapwood of all oak trees. The origin of the fungus is currently unknown, and although it has varying degrees of severity across the different species of oak, it appears red, black and pin oaks are most susceptible.
CFIA has implemented movement restrictions on the affected properties in Ontario in order to help prevent the spread of the fungus, which can kill a tree in just one season. CFIA is working with other federal, provincial and municipal governments to survey the area and determine next steps.
As the tree attempts to isolate the fungus, it also restricts water and nutrient flow, causing its health to decline. Affected red oaks are often identified with the disease through their pointed lobes. White and bur oaks can be identified by their rounded lobes. Leaf bronzing at the top of the tree, sudden wilt of a healthy tree, premature shedding of leaves in spring, summer or early fall, and vertical cracks in trunk bark caused by fungal mats are all signs a tree is likely infected.
The fungus can be spread naturally by small sap beetles (Nitidulid beetles). Wounded, pruned or harvested trees release a sap that attracts the beetles, who then transfer it when visiting a nearby healthy tree. The beetles do not typically travel more than a few kilometers. The fungus is primarily spread via direct contact of interconnected tree roots.
Members of the landscape horticulture community are asked to avoid harvesting or pruning oak trees from April to August when the beetles are most active, and to be on the lookout for affected trees. All possible sightings should be reported immediately to CFIA or the Invasive Species Centre (via their website or at 1-800-563-7711), CFIA, or by using the EDDMapS app.
Photo credit: Invasive Species Centre