By: Mackenzie DiGasparro, ISC Policy & Program Development Coordinator

In 2020, a collaborative project team with members from the Ontario Ministry of Natural Resources and Forestry, Natural Resources Canada, and the Canadian Food Inspection Agency found oak wilt fungal eDNA in Ontario. Oak wilt is a vascular disease of oak trees, caused by the fungus Bretziella fagacearum. The fungus restricts the flow of water and nutrients through oak trees, which causes wilting foliage, and eventually leads to tree death. In 2019, Insect traps used for sampling were placed in several locations near the US-Ontario border. Insects collected in the traps underwent genetic analysis to determine the presence of oak wilt fungal eDNA.

Oak leaf showing signs of wilting
Oak leaf showing signs of wilting

Insect samples were used to test for oak wilt eDNA because a key pathway of spread for this forest pathogen is the movement of insects. Sap beetles are attracted to the sweet smell of fungal mats found primarily on red oaks infected with oak wilt. They can then carry spores to the next healthy tree, depositing those spores into the fresh wounds that they are feeding on. Wounds on oak trees can either happen naturally or are human caused, for example, the pruning of an oak branch.

Does this detection mean that oak wilt is now present in Canada? The answer to that is no! A positive confirmation of oak wilt in Ontario would require the detection of symptomatic trees that are confirmed positive for infection as verified through genetic analysis.

So, what does the presence of oak wilt eDNA mean? The detection of oak wilt fungal eDNA in Ontario means that we must remain vigilant for the signs and symptoms of oak wilt in our communities. This result informs us that the use of traps and eDNA testing are an effective early warning system for this invasive forest pathogen. As a community member, be sure to be on the look out for the signs and symptoms of oak wilt, and to report any suspected finds immediately to the Canadian Food Inspection Agency.

At this time, there are several hypotheses as to how beetles carrying oak wilt eDNA have arrived in Ontario. It is unknown whether or not the beetles carrying the oak wilt fungal eDNA originated in Ontario or if they were carried by wind from an oak wilt infested site near the Canadian border.

Further research is currently being conducted to improve the efficacy of the use of traps as an early detection system as well as in surveying for infected oak trees in areas where oak wilt eDNA has been detected.

For more information on oak wilt and oak wilt fungal eDNA, read the Oak Wilt eDNA Frequently Asked Questions page here.

Nitidulid beetle carrying fungal spores
Nitidulid beetle carrying fungal spores

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