On a recent tree evaluation visit I discovered more fallout from the historic polar vortex freeze event in November 2014. Many of my contemporaries said we would continue to see more damage in otherwise apparently unaffected species and sure enough, now two seasons later, green ash trees are pushing off large sections of damaged bark.
|Bark loss from Callery pear observed in 2015|
This damage and the resulting recovery is similar to what we are seeing on ornamental pears but the symptoms have been delayed do to the difference in bark thickness of green ash. The South or Southwest facing sides of green ash trunks and branches had not gone dormant when the freeze event occurred and these portions of the vascular cambium were killed.
White ash trees were not affected but green ash trees growing
in warm locations, in this particular case street trees growing on a south
facing slope show considerable damage.
The marginal cambium that did not freeze
is now trying to grow over the damaged section of trunk wood and is pushing the
dead bark off in its attempt to close the wound. Another concerning symptom
that is explained by this freeze damage is the thinning canopy and decreasing
growth increments in affected trees.
We have had two cool wet springs that
should have resulted in fantastic growth in green ash and to see the opposite
has had me concerned. The elephant in the room anytime we discuss
symptomatic ash trees is of course the possibility of finding emerald ash
borer, especially in trees that are losing chunks of bark, have thinning canopies,
and dying crowns. The difference between freeze damage induced bark loss and
bark loss as the result of the exotic emerald ash borer is the absence of a zig-zag or meandering pattern visible both on the loose pieces of bark and exposed
wood caused by EAB larval feeding. Learn more about emerald ash borer at: eabcolorado.com
|Green ash with loose bark on the south side of the tree.|
|Thinning canopy and dieback on ash from the November 2014 polar vortex freeze event.|
|Ash tree attempting to close wounds from freeze injury.|
|Emerald ash borer feeding (photo courtesy of University of Minnesota Extension)|