February 5, 2024
Extreme
environmental conditions make Texas trees susceptible to secondary stressors
COLLEGE STATION, Texas—With three
consecutive years of severe weather conditions throughout Texas, including
extended hard freezes and droughts, East Texas trees have become vulnerable to
secondary threats. These threats include cedar bark beetles, Ips
engraver beetles, hypoxylon canker and cedar rust fungi.
Trees experience threats
like insects and diseases regularly, and when a healthy tree encounters these stressors
under positive conditions, they can show little to no reaction to the threat.
However, environmental conditions such as droughts, extreme winter weather and new
construction development can add primary stress to the trees. As the trees
encounter prolonged stress under these factors, they become more susceptible to
secondary threats.
Ben Plunkett, Texas A&M
Forest Service District Forester, explained that many secondary factors, like
insects and fungi, can almost always be found in forests throughout the state,
but healthy trees are not as threatened by them and do not indicate an
infection.
“We can relate these
secondary factors of trees to human bacteria,” said Plunkett. “If we cultured
every tissue on our body, we would probably find bacteria, but it will only
turn ‘toxic’ under certain conditions. Trees respond similarly in that weakened
trees will see an increase in reaction to the fungi and insects.”
Environmental conditions can
affect trees for years and decades to come. For instance, Plunkett noted that
the droughts of 2011 and 2015 are still oppressing the surviving trees today.
Allen Smith, Texas A&M
Forest Service Regional Forest Health Coordinator, reiterated this sentiment. “The
trees are under such severe stress that it takes one little additional factor like
a cedar bark beetle to push the tree into mortality,” said Smith.
Common fungi spread among
cedars in Texas are cedar rust fungi. Most commonly seen as cedar-apple rust or
cedar-hawthorn rust, these fungi are not deadly but can cause irreversible
damage. These fungi can cause leaf discoloration and “bleeding” cankers. Cedar-apple
rust is recognized by its distinct reddish-brown galls around young branches
and twigs that resemble the size of a golf ball.
Among the current most
threatening fungi to weakened hardwood trees in East Texas is hypoxylon canker. Symptoms of hypoxylon canker can
include browning of the leaves and sloughing of bark, which exposes a gray or
black fungus on the sapwood of the stem or major limbs.
Threatening insects to
weakened trees currently include Ips engraver beetles and cedar bark
beetles. Symptoms of Ips engraver beetles
occur in pine trees and include discolored crowns, dying branches and numerous
white to reddish brown pitch tubes on the bark. Adult Ips beetles are
cylindrical, measuring approximately 3/32” in length with a black to reddish
brown color.
Symptoms of cedar bark beetles occur in cypress and juniper trees and include
the discoloration and dropping of leaves; twig and branch decline; and small
exit holes present on the bark of trunk or limbs which are sometimes
accompanied by “sawdust” around the boring or tree. Adult cedar bark beetles
are approximately the size of a grain of rice with cylindrical bodies and a
reddish colored back.
In closing, Smith noted that
many of the trees that appear to be dying may experience significant recovery
this spring. The warmer, wetter and more stable weather conditions of the
spring will take environmental stress off the trees, allowing them more
strength and immunity toward secondary factors.
If Texas residents notice
repeated or widespread tree abnormalities in their community, Texas A&M
Forest Service local foresters are able to inspect and address specific
concerns. Find your local forester here: https://tfsweb.tamu.edu/contactus/location-search/
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