Beech Leaf Disease Found in Watershed

Close-up of tree leaves.

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.

Microscopic picture of an organism.
The nematodes viewed under a microscope.

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.

Close-up of three tree leaves.
American beech leaves showing signs of beech leaf disease with dark striping.
Leaves on a tree.
A thicker appearance of beech leaf disease.

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.

Person in forest closely inspecting a tree leaf.
Emily Stacy, a Watershed Monitoring Technician, inspecting American beech trees for beech leaf disease at Belfountain Conservation Area.

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.

It takes a community to protect a forest. If you have concerns about beech leaf disease, connect with us over Facebook, Twitter and LinkedIn.

By Mariann Lobbezoo, Assistant, Watershed Monitoring

Comments (4)

    1. Credit Valley Conservation

      Hi there. Unfortunately, beech leaf disease affects many species of beech, including beech cultivars such as copper beech. The tolerance of each species and cultivar to beech leaf disease is still not well studied so information is limited at the moment. Best way to keep you beech trees on your property healthy is to minimize stress to the tree (proper watering, mulching) to help maintain the natural defenses of your tree.

  1. For the first time my copper beech had a lot of nuts. Is this typical of beech trees? This tree is about 30 yrs. old and is in good shape. The leaves look quite healthy and are a shiny deep red colour. Are the nuts an indicator of some kind? Your comments would be appreciated.
    Thanks, R. Orida.

    1. Credit Valley Conservation

      Yes, this is typical of beech trees. Beech trees (including copper beech) and oak trees have a huge variation in the number of nuts they produce from year to year. When these trees produce a vast quantity it is called a mast year, which occurs every few years. Often with beech and oak trees, most trees in the area will have their mast year in the same year. 2023 was a mast year in Ontario, where higher numbers of oak, black walnut and beech nuts were produced on trees.

      There are various theories that try to explain why this happens and one of them is predator satiation. Trees produce so much food that the animals (squirrels, birds, etc..) cannot possibly eat all the nuts, ensuring some of them become seedlings the following year.

      Your tree sounds healthy based on your description, so I would say do not be concerned with the higher production of nuts this year, as this is a normal event that happens every few years.

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