What’s Poppin’? Beech Leaf disease

Photo: Science Friday

Outbreaks of tree diseases can leave forests scarred for decades. A hundred years ago, chestnut blight tore through our woodlands leaving American chestnut populations struggling. This caused a cascading effect of loss for forests as they thinned and animals lost a food source. Where it used to be impossible to miss American chestnut it is now a rare sight, with most dying of blight before they can make it past the sapling stage. Over the past decade, another disease has been on the rise in yet another prominent tree species in Northeast forests, this time American beech. The disease? Beech leaf disease.

Photo: SLELO PRISM

Beech leaf disease aka beech blight was discovered in Ohio in 2012 and is associated with an invasive species of nematode (a microscopic worm) called Litylenchus crenatae mccannii (LCM).

Carried from tree to tree by wind, rain, animals, or in transported firewood the LCM nematodes will parasitise the leaf buds of beech species, causing extreme cellular damage and acting as a disease vector. This damage leads to stunted and deformed leaves marked by dark green bands in spring and into summer, with further yellowing and die off in late summer into fall. At a larger scale, beech leaf disease thins the canopy and prevents trees from photosynthesizing properly. This lack of nutrients starves the tree and eventually leads to the death of the beech, with even mature trees dying in as little as 7-10 years.

Litylenchus crenatae mccannii (LCM) isolated from beech leaf tissues in the Rutgers Plant Diagnostic Laboratory.

There is still hope! Research is actively being conducted to find possible ways to stop the spread and find a cure to reduce the impacts of beech leaf disease. Studies on Japanese beech have found that it has a higher resistance to parasitisation than our native American beech, likely due to LCM being a native to Japan. This has sparked a joint effort between Japanese and American researchers to understand what gives Japanese beech this advantage.

Another avenue of research is chemical treatment. Most notably root flare injection (pictured below) is the practice of injecting a mix of fungicide and nematocide into the roots of the tree, allowing the tree to carry those chemicals up to their canopy to kill the LCM nematodes living inside their leaves. While this works wonderfully as a temporary solution, the results fade fast, with trees returning to standard state in just a couple years. Additionally trees injected with this mixture are still vulnerable to LCM to an extent. This means that surrounding infected trees can reintroduce the nematodes, kickstarting the infection again. At the moment this treatment is only really viable for small isolated stands of beech.

Root flare injection at Riverbend Park in Fairfax, VA.

Beech leaf disease range in North America as of December 2024. Photo: USDA Forest Service:

Other groups have set their sights on slowing the human induced spread of this nematode. Awareness campaigns like Don’t Move Firewood highlight how simple decisions like moving firewood from one place to another can have devastating impacts. Firewood can act as a vector for these nematodes, spreading them wherever the firewood is taken, infecting all the beeches along the way. This easy spread is what has allowed beech leaf disease and LCM to spread across most of the northeast, including every county in Pennsylvania.

So, what’s poppin? While high tech surveying methods like drones exist, citizen science has been a key tool in understanding and combatting beech leaf disease. Next time you are on a walk through the woods, look up into the canopy and see if you spot those tell tale dark green stripes. If you do, snap a photo and upload it to a citizen science platform like iNaturalist to share data with the rest of the community. With just a couple seconds of your time you can help the fight against beech leaf disease.

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By Erin Leland