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.
