What is Up With Beech Leaf Disease?

Close your eyes and picture a forest. What do you see? 

Each person will probably have a slightly different scene in front of them. For some it might be expanses of tall dark pines, for others mixed leafy deciduous trees bright green leaves shimmering in the sun, some might see a jungle and others giant cedars. The main thing is this: though a forest is made of many key elements it is defined and dominated by its trees. 

Trees are not only a key part of natural ecosystems but also crucial to modern people. From providing shelter, to recreation, and lumber and paper for our everyday lives, healthy forests help us live a better quality of life. 

One tree that has a long history with us, and that faces a new threat, is the beech tree. This iconic deciduous tree is under threat from disease caused by an invasive nematode. So, what can we do to stop it? 

All About Beech Trees 

Beech trees are widespread deciduous trees in the genus Fagus. There are 14 species of beech tree but for this case study of beech leaf disease we are mainly referring to American beech (Fagus grandifolia –native to NA) and European beech (Fagus sylvatica – cultivated around much of the world). Beech trees are quite easy to spot if you know what to look for. 

Here are some key points for beech tree identification: 

• Grey bark that gets darker with age
• Bark is very smooth
• Large oval green leaves – uniform in color (when healthy)
• Leaves have jagged edges ending at each leaf vein
• Fruit is a greenish prickly triangular nut known as beech nuts

It is also helpful to note that most Beech trees hang on to their leaves through the winter. They do not stay “evergreen” but unlike most deciduous trees you will see their reddish-brown leaves still clinging onto the branches through the colder months. The process of hanging on to this otherwise dead vegetation is called marcescence. 

Beech trees provide a crucial resource to animals that feed on beech nuts and are really important lumber species for us. Making it even more important that we work to conserve them. On that note, some beech trees in North America are in trouble, which is concerning for natural ecosystems and for cultivations of this important lumber species. 

What is Beech Leaf Disease 

On the surface, beech leaf disease (BLD) looks like odd striations on the leaf. Normally beech leaves are a uniform color but infected leaves will have dark lines along some of their veins. This forms a stripe-like pattern. These leaves may also be leathery, curled up, and appear a bit “sickly.” If a leaf is damaged enough it may even drop right off the tree.  The disease does not kill the tree directly, but instead slowly chokes off its resources by rendering its leaves less efficient in photosynthesis. 

For a while the trees seem to be able to handle some of this stress, but many will die in a few years due to the continued stress. Younger trees are particularly vulnerable as they already face a disadvantage of being smaller, weaker, and trying to grow below the canopy where light is already limited. 

So what is going on? 

For a while researchers had no idea what was happening, but after taking samples of infected leaves back to the lab they soon found the culprit – a nematode called Litylenchus crenatae ssp. Mccannii. Nematodes are tiny worms, many of which are parasitic like the ones causing beech leaf disease. These little worms feed on the growing bud of new leaves which is what causes the leaves to come out damaged in the spring. 

What is being done: Beech leaf disease research

This nematode seems to have started out of Ohio and is now spreading East and Northeast so it is important to track and slow down the spread. 

Researchers such as Dr. Kayla Perry of the Perry Lab In The Department Of Entomology at The Ohio State University are working on understanding these nematodes, their life cycle, and how they spread. Studying the life cycle of these tiny worms and how they respond to various treatments can help the researchers find the most effective way to treat infected trees and prevent the infection of new ones. After trials in the lab, organizations then scale up the most effective strategies so that they can be applied in real forests, stopping beech leaf disease in its tracks. 

Though research is still in progress, a few promising treatments are out there. Such as:

• Thiabendazole injections to protect healthy trees,
• Application of potassium phosphite into soils to boost tree resilience
• Nematicides (pesticides specifically for nematodes) to help control the nematode population in infected trees. This reduces the risk of spread to other trees. 

What you can do

You don’t have to be a scientist to help out beech trees. A really important part of this research is actually knowing about the spread of beech leaf disease. If you see trees that appear to be infected you can report it to your local forestry department or a lab that is studying BLD. For example here is a link for reporting in Michigan. By reporting beech leaf disease you can help researchers and organizations track the spread. With this information groups know where they should focus their resources. 

In general, by going outside and getting to know your local area you can help conserve them. Whether it sounds cheesy or not, the world is a better place when we are all stewards of the land. 

In Short

Beech leaf disease is a threat to beech trees in Eastern North America caused by an invasive nematode that damages leaves during budding. Though some trees are able to live with this stress, many trees die within a few years of infection. Researchers are working hard to understand this disease and how best to control it. There is no current solution but there are various promising treatments and deterrents on the horizon. You can help your local forest by keeping an eye out for beech leaf disease and reporting it. Though the threat is intimidating, with more research and support scientists can work to stop beech leaf disease in its tracks and protect our beloved forests.