Invasive Tree Disease Discovered for the First Time
For the first time, CVC staff detected beech leaf disease (BLD) within the Credit River Watershed. BLD is an emerging invasive forest pest spreading through Ontario. BLD was detected this fall at Belfountain and Limehouse Conservation Areas through our Integrated Watershed Monitoring Program.
What is Beech Leaf Disease?
BLD infects American beech trees (Fagus grandifolia). Nematodes, tiny worm-like organisms, are involved in spreading the disease. This nematode species (Litylenchus crenatae subspecies mccannii), feeds on the leaves of infected trees. American beech infected with BLD experience branch dieback and tree mortality. Research is ongoing to fully understand the mechanisms of this new disease.
How to Recognize the Signs of BLD
Some infected trees do not show signs of BLD, or signs are only apparent on select branches. According to research, nematodes survive the winter in branches and infect new leaves the following season.
On beech trees that do show signs of BLD, look on the leaves for:
- Dark stripes between leaf veins, this is an early sign of infection.
- Leaves developing a thick and leathery texture, indicating infection is progressing.
These signs will appear on leaves during growing season and on dead leaves over winter.
A Double Whammy: BLD and Beech Bark Disease
In addition to BLD, beech trees face another threat: beech bark disease. Currently, 92 per cent of beech trees monitored throughout the watershed show signs of beech bark disease. Beech bark disease primarily kills mature trees, while BLD primarily kills young trees. Approximately one per cent of beech trees are resistant to beech bark disease. However, it’s unlikely that these trees are also resistant to BLD. The future of beech trees is at even greater risk because of this pest combination.
These diseases pose a threat to our forests, as beech trees are a major component of the canopy. Squirrels and birds, among others, depend on beech trees for both food and habitat. When beech trees die, invasive species like common buckthorn (Rhamnus cathartica) can invade the understory and outcompete native plants. The loss of beech trees will result in reduced biodiversity in our forests. This weakens the forest’s ability to withstand future pests.
How CVC is Responding to These Threats
CVC tracks the presence and spread of forest pests and diseases throughout the watershed by monitoring tree health. Using this data, we measure the impact of forest diseases like BLD and beech bark disease. Currently, there are no management tools available to control this disease other than reducing its spread.
How You Can Help
Ways you can help protect beech trees and reduce the chance of spreading BLD include:
- Don’t move soil, leaves or firewood from one area to another.
- Stay on designated trails.
- Clean your boots, clothing and equipment after hiking.
- Report potential sightings using EDDMapS, iNaturalist, or email us.
By Mariann Lobbezoo, Assistant, Watershed Monitoring