Riddle Me Beech

What do we do about a plant disease we don’t fully understand? This is the difficult situation surrounding a new problem called beech leaf disease.  While it hasn’t been reported in our part of the Hudson Valley yet, it did turn up in New York State in 2019, so I’m going to put it on my tree-problem-worry list and hope I never really have to learn about it.  While I’m not asking you to do the same, if you see something strange happening to a beech tree next summer, please give us a call.

The mystery ignited in 2012 when a biologist in Ohio’s Lake County noticed something odd happening to native beech trees (Fagus americana) in woodlands and well as in landscapes.  Starting in the spring, the leaves of impacted trees took on a strange, striped appearance due to darkened bands between the leaf veins.  These areas eventually turned yellow, crinkly, and leathery (see photo above, from The Ohio State University website at:  https://bygl.osu.edu/node/1176)

.  Heavily damaged leaves curled and dropped off the trees prematurely.  With time, it was seen that young trees started to die within three years of the first symptoms.  The diseased trees were also more susceptible to the myriad of other problems beeches face, which includes mites, aphids and many problematic fungi.  Perhaps the worst actor in this cast of characters is beech scale, an insect introduced into Nova Scotia in the 1890’s which has since marched westward, and opens up trees to infection by a fungus called nectria canker.  This insect-fungus tag team is called beech bark disease and has harmed local beeches for about the last 50 years.    

If all this wasn’t enough, next enter the foliar nematode.  These tiny creatures infect plant foliage, causing patches leaf cells between leaf veins to die.  The damage caused by a foliar nematode looks strangely similar to the beech leaf disease, so researchers began looking for nematodes in beeches, something which had never been seen in the United States before.  They soon hit paydirt, discovering that our American beeches were harboring an organism called Litylenchus crenatae, an Asian beech tree nematode.  So were these the cause of beech leaf disease?  To find out, scientists extracted nematodes from unhealthy trees and injected them into clean trees growing in a greenhouse.  These clean trees then developed the disease, leading researchers to pronounce the nematode the culprit.

Not so fast, say rival researchers from The Ohio State University (disclaimer:  my alma mater and a very fine institution).  They’ve discovered examples of both healthy and unhealthy beeches harboring the nematodes, and additionally found three suspicious types of fungi and three questionable types of bacteria in diseased trees, all of which muddies the waters but might indicate multiple causes for beech leaf disease.  Hopefully, researchers will agree on a cause soon, since we need some treatments for the problem, which has spread rapidly since 2012 into parts of Pennsylvania, Ontario, and our Long Island and lower Hudson Valley.  For Fagus americana, one of our grandest native trees, life is indeed becoming a beech.