Two diseases invade Ontario beech forests

Walking on a sunny winter day in Twin Oaks Woods, I was struck as always by the glow of the beech leaves that hold onto the trees all winter long. It’s one of the reasons I love the American beech, Fagus grandifolia, besides the smooth touch of their grey bark, the photogenic spiny beechnuts that attract birds and animals, the tawny natural dye available from winter leaves, and the list goes on. I snapped a photo and went home to process it and share the beauty.

Only then I noticed something that shouldn’t be there. Check the photo above. Four trees on the left show a dusting of white fluff up and down their trunks. I had seen it previously on one tree near the footpath, but didn’t realize what it was. At the time I thought, “Some kind of fungus?”

Woolly beech scale and canker caused by a bacterium cover this tree's bark, hallmarks of beech bark disease.

At the time I thought, “Some kind of fungus?”

That came as little surprise. Several years ago a plague of emerald ash borers tore through this woods. Since then all the mature ash trees have perished. Waterloo city workers cut down the ones dangerously near the trail, leaving remote standing snags as homes for woodpeckers, owls, and other wildlife. All kinds of fungi are feasting on the dead trees. Meanwhile I hoped this troop of small beeches was well positioned to fill the new openings in the canopy.

They never will. Last summer this new fluffy white stuff spread to more beeches. I hadn’t noticed because there were too many leaves, not until winter peeled away foliage, opening the forest to be seen more clearly. I realized immediately this infestation was something serious, so I uploaded a photo from my phone to iNaturalist too see if it could be identified.

The news that came back made my stomach hurt. I kept reading for something more hopeful, but the outlook is bad. That fluffy white stuff is the protective covering for woolly beech scale, Cryptococcus fagisuga, an insect that sucks nutrients from the tree. Not only that, but their puncture wounds admit a fungus into the tree, Nectria faginata. It colonizes the sapwood causing cankers that deform the bark. This complex called beech bark disease has invaded Ontario recently. It can take five or six years to kill the tree. Working together the insect and fungus completely girdle the tree so nutrients can’t reach the canopy.

Woolly beech scale insects allow the fungus to get inside, causing cankers in the adjacent bark.

…their puncture wounds admit a fungus into the tree, Nectria faginata. It colonizes the sapwood causing cankers that deform the bark.

The beech trees in this woods will die, nearly all of them. There is no effective treatment for an infected tree in its natural setting. If beech scale appears on individual landscape trees, they may benefit from gentle water spray and brushing to remove the insects. Severely affected and dead trees should be cut down, but avoid transporting the wood to other areas.

The Government of Ontario website provides a fact page on beech bark disease, delivering the prognosis that it’s moving through the tree’s entire range in Southern Ontario. In fact it has been moving west from Nova Scotia since the late 19th Century and is expected to reach all beech forests in southeastern North America eventually.

The fungus Nectria faginata attacks sapwood, causing cankers that girdle and eventually kill the tree.

The beech trees in this woods will die, nearly all of them. There is no effective treatment for an infected tree in its natural setting.

The disease has some characteristics we can use against it. These scale insects can’t fly, so the disease is slow-moving. Young trees up to 30-years-old seem to have a natural immunity, perhaps producing a chemical that prevents attack. Finally, about one percent of adult trees seem immune because their bark is too smooth for the insects to find a purchase.

However, beeches are set to receive another punch. While researching this post, I learned about another plague reaching our provincial borders at the same time. The Government of Ontario also has a fact page on beech leaf disease. It is caused by a nematode worm, Litylenchus crenatae mccannii, newly identified. The disease appeared in Ohio in 2012. Even worse news for our beech groves: the disease attacks and kills young trees in particular, and it is moving quickly through the tree’s range, afflicting both American beeches and European beeches used in landscaping.

10 wildlife species that depend on beeches

Why should we care about beech trees? Besides their beauty, they play a significant role in temperate deciduous forest ecology. Let’s consider their importance as a food source alone. According to First Light Wildlife Habitats, beech nuts contain “about twice as much protein and calories per edible portion” as the next most important tree nut, acorns. Wildlife food studies found they were a significant part of the diet of these 10 mammals and birds, to name a few:

  • black bear (25% to 50% of the diet!)
  • porcupine
  • flying squirrel
  • red squirrel
  • eastern chipmunk
  • ruffed grouse
  • wild turkey
  • wood duck
  • rose-breasted grosbeak
  • blue jay
Beechnuts contain more nutrient value than acorns.

Beechnuts contain higher nutrient value than acorns and can comprise 25 to 50 percent of the diet of black bears.

How to protect beech forests

Humans are largely responsible for moving these invasive pathogens around. Beech bark disease and beech leaf disease may devastate our woodlands before effective medicine is found. However, we must still practice good forest hygiene to slow their progress and prevent unnecessary infection.

  • Don’t transplant beech saplings between locations.
  • Don’t transport firewood or brush into another forest area.
  • In managed woodlots, preserve and protect any beeches that survive the disease and appear uninfected. These trees may foster a resistant population.

For more information:

Natural Resources Canada has further information on managing beech scale infestation.

Michigan State University Extension provides a detailed PDF, Biology and Management of Beech Bark Disease.

The Invasive Species Centre provides more information on Beech Leaf Disease.

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