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Aerial Assault: Dead and Dying Ash Trees Pose Hazard from Above

August 09, 2017 12:00 PM

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​Responsible for hundreds of millions of recently dead and dying ash trees, the emerald ash borer (EAB) is a destructive, invasive insect from Asia.The beetle was first discovered in the United States in Michigan in 2002. Now, the EAB has spread to nearly half of states in the U.S., including Pennsylvania in 2012.

Their destruction is vast and very noticeable, and to make matters worse, the dead ash trees they leave behind are extremely dangerous. Falling branches and trees can result in injuries and even death, so this is an issue that should not be taken lightly across the commonwealth.


What can private landowners with ash trees do? Inspect your trees.

Given the widespread nature of the EAB infestation, private landowners should be wary of their ash trees, especially those that seem to be in declining health. All ashes that are a liability for human injury or property damage should be evaluated and potentially targeted for removal.

If you have ash trees that still look healthy, there are effective insecticides, such as imidacloprid and emamectin benzoate, that can protect them. In this case, DCNR recommends that you talk to a tree care professional.

Ashes showing significant signs of stress are likely not worth trying to save, and should be removed if they pose a threat.

If you have ash trees on your property that are dead -- showing no green leaves at all -- you should get the tree removed immediately.

Landowners are urged to allow a professional tree service to do the removal; these companies have the appropriate equipment and follow necessary safety procedures.

Landowners can also contact DCNR’s service foresters (PDF) for help or advice.

What does the destruction look like?

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During its larval stage, the EAB feeds on sapwood just inside the bark, cutting off vital, conductive vessels that enable photosynthesis and life above in the canopy. A zig-zag feeding pattern called a “gallery” will remain.

This leads to “die-back” in the canopy, where progressively larger branches lose vigor, eventually becoming brittle and dangerous. Adding to the hazard, ash carries much of its mass in heavy, main stems.

It is not uncommon for standing-dead ashes to break off along their trunk, leaving massive, crownless snags. Over time, an infested stand of ash becomes a graveyard of fallen or standing-dead trees, also known as “widow-makers.”

These trees pose a real threat, especially as the trees will die and fall down on a landowner’s property.

Donald Eggen of the DCNR Bureau of Forestry’s Division of Forest Health shared that ashes become weaker from the initial time of infestation, becoming more susceptible to stem breakage and windthrow during windy conditions.

Eggen also noted a recent uptick of accidents among arborists throughout the ash/EAB range in the U.S., a spike he attributes to the inherent danger in dealing with the massive population of dying ashes.

Chad Voorhees, also of DCNR’s Bureau of Forestry, notes that he observes dead and dying ashes on “every trip” to Pennsylvania state forests, while citing a statewide surge in ash salvage sales associated with the EAB outbreak.

What does this mean for Pennsylvanians? We need to be aware.

EAB die back.jpg
Millions of ashes still stand in Pennsylvania, representing a threat to human safety and property. Because ash was popularly planted in suburban settings decades ago, the threat is not limited to forested settings.

Anyone living in the range of the EAB, while spending considerable time outdoors and/or managing land, should be aware of the risk and how to identify weakened ash trees.

There are many signs and symptoms of infestation (PDF). Some things you can look for include:

  • Crown/canopy die-back
  • “Blonding” of the bark or bark splitting
  • Epicormic branches (stubby branches)
  • Excessive accumulation of fallen branches
  • D-shaped exit holes
  • Serpentine galleries

DCNR management of ash resources

DCNR has been proactively managing ash resources (PDF) to minimize risk to state forest and park users. Many similar projects are slated or underway. Current and recent ash projects on state lands include:

  • A current project in the Wertz tract of the William Penn State Forest targets 440 ashes along a hiking trail to minimize the threat of branches falling on hikers.
  • A timber salvage operation at Tyler State Park in January 2017 removed one thousand hazardous ash trees within high human-use areas.
  • In the Tioga Forest District, hazardous ashes were removed along 8.75 miles of the Pine Creek Trail during the winter of 2015.

Sadly, EAB has devastated Pennsylvania’s ash resources. From a forestry-action standpoint, the days of quarantine seem a distant memory. DCNR recommends that landowners – if they haven’t already done so -- should adopt a strategy that emphasizes mitigation of ash danger, as part of a broader plan in addressing EAB’s destructive aftermath.

For help with that strategy, contact your county’s service forester (PDF) or DCNR’s Bureau of Forestry.

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