Ash Issues Abound
Southwest Yard & Garden
by Dr. Marisa Thompson
Question: Half of my ash tree looks ok, but the
other half looks completely dead. What could be the problem? Is it going to get
worse or better?
- Mike N.,
Placitas, NM
Answer: (Throughout this column I’ve added links to more information from related columns I've written that might be helpful.)
Ash trees are worrying homeowners all over the
state. Bernalillo, Sandoval, and San Juan County Extension Agents Sara Moran,
Lynda Garvin, and Bonnie Hopkins, respectively, reported that they’ve been
getting more and more calls about ailing ashes in those areas in the past few
years. Jimmy Zabriskie, Community Forester with the City of Las Cruces Parks
& Recreation department says he has noticed stressed ash trees on both
public and private property, some with evidence of borer damage. In severe
cases, trees will be removed in the coming weeks and Zabriskie plans to look
closely at these tree roots in hopes of understanding the underlying causes for
their recent decline. A friend in Truth or Consequences texted me photos of her
three ash trees—two of which are only a few years old—have lost half of their
canopy from the top down and have trunks that are riddled with borer holes the
size of BBs which we determined to be caused by the ash twig borer. The third
tree is 30-feet tall and is looking gorgeous without any outward signs of stress.
Another report came from the west side of
Albuquerque where a tree owner is alarmed because part of the canopy has
tightly curled, contorted leaves, and on a few branches the leaves are barely
recognizable wisps. And yet another ash in Belen leafed out very late this
year, and now half its canopy has leafed out and is looking beautiful and healthy,
but about a quarter of the canopy has died back to the larger branches, and on
the final quarter there are sea anemone-looking stunted growth clusters
spurting out where the new season’s branches and leaves should be. Dr. Carol
Sutherland, NMSU Extension Entomology Specialist, lamented, “Unfortunately, ash
trees are a virtual magnet for insect pests.” Sutherland adds, “The world is
‘smaller now.’ We have pests (like ash whitefly) that weren’t here 30 years
ago. Expect more exotic pests to arrive and for pest distributions to shift in
the coming years.” Among the possible culprits are whiteflies, ash twig beetle,
ash/lilac borer, emerald ash borer (not yet), and aphids.
Ash trees are a popular pick for yards and parks for
several reasons. They’re fast growers that can produce a nice, rich shade in
under a decade if (and it’s a big if) they’re planted correctly, well cared
for, and left alone by pests. All ash trees are in the Oleaceae (olive and
lilac) family, and species commonly planted in New Mexico include the Arizona
or velvet ash and associated cultivars (like the popular Modesto ash), green
and white ash, Raywood ash, fragrant ash, and others.
Jennifer Dann, Urban and Community Forestry Program
Manager for NM State Forestry, points out that, in addition to their bright
green leaves, the seeds, and fruit aren’t overwhelming from an upkeep
perspective; they’re native to the United States; the Arizona ash is even
native to New Mexico; they aren’t invasive or poisonous, and they don’t try to
stab you.
Last year, with US Forest Service Funding, Dann and
collaborators inventoried 200 tree species in established public spaces in each
of our 33 counties. Fraxinus, the genus for all ash species, was in the top
five most common tree genera (plural of genus) statewide. Can you guess which
other genera made it into the top five? Think about the oldest park in your
vicinity. Now visualize the oldest trees in that park and you’re likely
thinking of one or more of them: mulberries (Morus spp.), pines (Pinus spp.), cottonwoods
(Populus spp.), and elms (Ulmus spp.). The results from the statewide urban
tree inventory are available to the public in the form of a story map. Visit
https://tinyurl.com/urbantreesnm to access all the details.
We have a tree problem in our public parks—actually
several problems. Old age is a serious issue. No tree lives forever, but many
of our ashes are dying way too young. Another issue is that too few of the most
common tree species are native to our region. And all five of those top five tree
genera consist of wind-pollinated species, so they’re not as supportive of
pollinating, beneficial insects as they could be. Having too many of only a few
species means the parks have low species diversity, which can lend itself to
all sorts of negative effects. For example, when the emerald ash borer gets toNew Mexico, or another insect pest population climbs sharply as a result of
warming temperatures, huge numbers of ash trees will be vulnerable. This
dreaded emerald ash borer has already killed hundreds of millions of ash trees
in North America since its introduction from Asia in 2002 and is expected to
kill billions more in the coming decade (yes, billions). As of October 2018
it’s now found in 35 states and as close as Denver, Colorado.
The solution to our aging park tree conundrum isn’t
as simple as planting lots more trees, although that is one of the steps.
Selecting a diverse mix of recommended species is another crucial step. “Right
tree right place” is the slogan and mantra for arborists worldwide for good
reason. Add in proper planting, adequate irrigation, and strategic (and ideally minimal) pruning and we’ll be well on our way to sustainably
increasing our urban canopy cover.
OK, back to the original question… is your ash tree
failing? Here are some things to double and triple check to help with
diagnosis: Is the entire root area and not just the trunk being irrigated in
a way that allows water to seep down over a foot deep? Are you watering too frequently? Is the tree planted too deep? Are circling roots cutting off
water and nutrient circulation underground? Sun scald? Or, like the little ash
trees in Truth or Consequences, does yours have evidence that ash twig beetles
caused branch dieback?
An ash twig beetle caused dieback on this branch in Belen. At the branching node the beetle chewed a groove all the way around the branch, girdling it. Photo credit M. Thompson.
Jennifer Dann suggests if branches are really dead, and not just leafing out really late, talk with a professional about whether pruning the dead out of the tree is a viable option for leaving a structurally sound tree in place, or whether the tree needs to be removed and replaced with something else.
Dr. Sutherland again, “Our best technology (applied
in human health situations) is not adaptable (at least yet) to plant problems.
We cannot see the roots, so we don’t know how large or widespread or numerous
they are. Are they healthy or do some have problems of various sorts? We cannot
look under the bark or into the woody interior---or take a ‘sap pressure’ like
our doctors take a blood pressure reading. We can’t stick a thermometer
anywhere into a tree to see what’s happening.” By the time we notice that our
trees are ailing, it’s likely that a lethal amount of damage may have already
been done. We need to plant smarter and pay closer attention to the details
from leaf symptoms to watering methods.
Here’s
what NOT to do: Spray an insecticide without knowing exactly what the pest is
or understanding its lifecycle. If it’s a secondary issue, the primary issue
(again, likely a water issue) should be addressed first. And hold off on
applying fertilizer. As retired NMSU Extension Horticulture Specialist Dr.
Curtis Smith says, “Think of fertilizer like you think of ice cream. When
you’re feeling healthy and strong, ice cream can be a nice treat. But if you’re
not feeling great, health-wise, it’s probably not the best choice.”
These photos from Belen of an ash tree trunk taken from different angles demonstrate no damage on the northeast side (left) and sun scald damage on the southwest side of the trunk (right). Photo credits M. Thompson.
Send
gardening questions to Southwest Yard and Garden -
Attn: Dr. Marisa Thompson at desertblooms@nmsu.edu,
or at the Desert
Blooms Facebook page (@NMDesertBlooms)
Please
copy your County
Extension Agent and indicate your county of residence when you
submit your question!
For
more gardening information, visit the NMSU Extension Horticulture page
at Desert
Blooms.
Edible New Mexico Magazine article crosslink -- GROWING YOUR FUTURE FAVORITE TREE
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