By Chris Hart
As autumn approaches, leaves will soon begin to change from vibrant greens to a fiery spectrum of yellow, orange and reds. Eventually completing their cycle as they brown and fall to the ground. But what if they skipped a step? What if, as you pass by one of the many beautiful oaks in our area, you notice that many of its green leaves are already beneath your feet? This could be a sign of oak wilt, and it is important that people are aware of the signs, symptoms and how to report it.
Oak wilt is a vascular disease of oak trees caused by the fungus Bretziella fagacearum growing on the outer sapwood and restricting flow of water and nutrients throughout the tree. This will result in the death of the tree, often within a year. White oak species (Bur, Chinkapin, and Swamp White) are more resistant than the red oaks (Black, Pin and Schumard), which can succumb to oak wilt within 2-6 weeks.
Countless oak trees have been lost to oak wilt in the United States since the 1940s, with confirmed cases in 24 states, including Michigan. With the presence of oak wilt close to the border, most notably for us on Belle Isle, the Canadian Food Inspection Agency (CFIA) began to form our country’s Oak Wilt Response Framework in 2016. In June 2023, the inevitable finally happened when three infected red oaks were found in the backyard of a Niagra Falls residence. The cracked bark and fruity smell were immediately reported to the CFIA, and within two weeks, the large trees were removed and safely disposed of. Surveys on oak trees in the area are still on going to ensure no further spread. Since then, two other cases have been reported, and managed in Springwater and Niagra-on-the-Lake.
The signs of infection to look out for include the wilting and dropping of leaves, starting at the top of the tree. The leaves will also begin to brown along the edges, with the discolouration moving inward. Vertical cracks will then begin to form in the bark as the fungal spore mat grows and pushes outward. It is at this point Oak wilt is at risk of spreading, as small beetles, attracted to the ‘fruity’ smell of the fungus, will enter the cracks to feed, and then disperse to other oaks covered in spores. Should a neighbouring oak have any recent wound in its bark, from pruning, storm damage or vandalism, then they too could become infected. Neighbouring oaks are also at risk of infection through root grafting. This is when intersecting roots of different trees join to assist with nutrient exchange.
If you notice any of the signs or symptoms mentioned above, or have any suspicion of Oak wilt, it is crucial that you report it immediately to the Canadian Food Inspection Agency. You can Google “CFIA Report a Pest” or use the link below. To make a thorough report, they ask that you include a variety of photos in order to properly and efficiently assess and triage the situation. Photos should be of the leaves, the canopy, the bark (including any suspected cracks), the base of the tree (to show fallen leaves), and also the entire tree, and surrounding area (to create the “bigger picture”). Any known history or background info on the tree should also be included.
The flight period of the beetles that transfer the fungal spores is from April to October. To help prevent the spread of oak wilt, pruning of oak trees should only be done between November and March. If a tree does receive a wound outside of the ‘No Risk’ period, pruning paint should be considered. It is also an important reminder to never travel with your own firewood. A study of US State Parks found that 25% of visitors brought their own firewood, and of the 25%, 55% came from areas with known cases of oak wilt.
For more information, including how to report oak wilt can be found on the CFIA website here. To learn even more, an extensive list of resources can be found on the Invasive Species Centre website here.
Information for this article was sourced from an Oak Wilt training seminar with representatives from CFIA, ISC and US DNR-Parks.