Leaf discoloration caused by oak wilt. Please note that there are many factors that may cause discoloured oak leaves, including drought. Source: Invasive Species Centre
Ontario residents are being asked not to prune their oak trees until November to help prevent the spread of oak wilt, a fast-moving and deadly tree disease.
The Invasive Species Centre says oak wilt is caused by a fungus that disrupts water and nutrient flow in oak trees. Once infected, red oaks can die in as little as two to six weeks. “The loss of oak trees can be felt in both urban and natural spaces,” said Colin Cassin, executive director at the Invasive Species Centre.
Oak wilt spreads most easily through fresh tree wounds created by pruning. These wounds attract sap beetles, which carry the fungal spores from infected trees to healthy ones. To avoid attracting beetles, residents are urged not to prune or damage oak trees between now and November when beetle activity is low.
If pruning is absolutely necessary during the high-risk season, experts recommend applying a thin layer of wound paint or shellac immediately after pruning.
Oak wilt was first detected in Canada in 2023 in Niagara Falls and has since been confirmed in other Ontario communities. It has also spread across 24 U.S. states, including Michigan, Ohio and New York.
Residents are also urged not to move firewood and to report signs of infection-such as wilting, leaf bronzing, or fungal mats-to the Canadian Food Inspection Agency.
For more information and resources, including webinars and training, visit the Invasive Species Centre website at www.invasivespeciescentre.ca.
(Written by: Joseph Goden)
