America’s urban forests are under attack.
Since 2002, millions of native ash trees across the nation have died and been removed. The culprit, an invasive beetle about as big as a thumbnail, is spreading across North America at an alarming rate and has recently been discovered at Virginia Tech by a graduate of the College of Natural Resources and Environment.
The emerald ash borer has caused significant damage to many of the country’s urban forests already. Ash trees that have stood for decades are found dead with intestine-like paths burrowed under their bark where the borers chewed through the trees’ water and nutrient conducting tissues.
Such damage has led large cities to set aside significant funds to prevent further destruction as well as to cover the costs of removing and disposing of dead trees.
Recently, arborists were distressed at finding exactly that infestation in ash trees of the New River Valley.
When Michael Webb, who graduated with a bachelor of science in forestry in May 2016, heard about the encroaching infestation, he began studying the insect in hopes of identifying any other infestations.
While there are limited means of preventing infestation, it is still crucial for arborists to have data on the trees in order to track the borer’s spread. Having been provided with an in-depth understanding of urban forestry, soils, and pest management by his studies at Virginia Tech, he was up for the task.
Webb is a plant health care specialist for Bartlett Tree Experts in Roanoke and encountered emerald ash borer for the first time in early May 2016. His first discovery of the insect was in Roanoke, where he identified the borer’s signature D-shaped emergence holes in an immature ash tree on a client’s property. He also discovered an infestation in Salem.
These discoveries inspired him to do further research and inspect similar ash trees in the area for infestation, including in Blacksburg.
“I discovered emerald ash borer on ash trees located on a greenway beside Blacksburg Christian Fellowship on North Main Street,” Webb said. “This led me to investigate ash trees on the Virginia Tech campus.”
Upon inspection, Webb found emerald ash borer infestations on ash trees near Norris and Cheatham halls. Webb contacted his former advisor Eric Wiseman, associate professor of urban forestry and arboriculture in the College of Natural Resources and Environment, for advice.
At Wiseman’s recommendation, Webb contacted Eric Day, manager of Virginia Cooperative Extension’s Insect Identification Lab in the College of Agriculture and Life Sciences’ Department of Entomology, who confirmed that what Webb found was, in fact, emerald ash borer.
Day promptly reported the infestation to the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service, which is the lead agency tracking the insect.
Wiseman then passed the information to James Bock, a plant health care specialist with Virginia Tech’s building maintenance and grounds unit in the Facilities Department.
Bock and his unit took immediate action, beginning with an inventory.
They found that every one of the ash trees on campus had been infested to some degree. On seven ash trees where adult borers were found active, insecticide was applied to the bark and branches to reduce the adult population available for breeding. Trees with minor degrees of infestation were treated with systemic insecticide via soil drench or trunk injection — environmentally friendly options that are preferred over aerial sprays.
Despite all efforts, 35 ash trees had to be removed. Fortunately, the number and diversity of trees on campus means that Virginia Tech’s overall landscape is not significantly affected.
“The criteria for removal was more than 25 percent crown loss, as this is effectively the point of no return,” Bock said. “Unfortunately, this is not a pest that can be treated one time to solve the problem; preventing future infestations requires annual or biennial treatments for the foreseeable future. The final number of trees to be preserved long term is approximately 30, and these are of varying species, age, and size.”
When it comes to the protection of ash trees, Webb and Bock emphasize the importance of catching the borer early on, as preventative treatments are far more effective than restorative ones. Thanks to Webb’s identification of the borer on campus, many trees will be saved.
For more information on the emerald ash borer, refer to the Virginia Cooperative Extension publication ENTO-76NP, “Emerald ash borer control for foresters and landowners.”
Written by Megan Maury Church of Fredericksburg, Virginia, a sophomore majoring in communication studies in the College of Liberal Arts and Human Sciences.