How To Spot Emerald Ash Borer Damage On Trees

Take a stroll through your community and you'll likely pass beneath the canopy of an ash tree or marvel at these trees that bring color to your autumn garden. Ash trees, commonly planted on city streets and in parks, offer us shade and oxygen, while also providing food and shelter for wildlife. However, the health and presence of these trees have been swiftly dwindling since the arrival of emerald ash borers (EAB) in 2002. These invasive pests, surprisingly beautiful with their slim, glittery shells, measure only ¼ to ½ inches long and can wreak havoc on even the most established ash trees. 

House Digest spoke exclusively with Andrew Conboy, an ISA-certified arborist based in Philadelphia, about detecting EAB damage and treating an infestation. "The earliest signs of emerald ash borer (EAB) infection on an ash tree are crown dieback (sudden increase in dead branches in the tree's crown), increased woodpecker activity (as they hunt for the EAB larvae), and epicormic sprouting (new shoots sprouting out of the trunk, larger branches, or at the tree's base)," Conboy said. He added that these pests will leave behind holes throughout the trunk, indicating where insects are emerging from the tree. 

"If you locate any of these D-shaped holes, that's a clear indication of EAB infestation," he said. "For the most part, other ash pests are native species that typically don't cause large-scale dieback or a sudden sharp decrease in tree health. If you notice these issues, those are good indicators as well."

Once you identify signs of an emerald ash borer infection, treatment is an absolute must. "Unfortunately, over 99% of most native ash species won't survive an infection, so treatment is really the only way to keep your infected tree alive," Andrew Conboy shared during his exclusive interview with House Digest. "If you catch the infestation early before a good portion of the tree dies, treatment can help keep the tree healthy for a while."

If at least half of the tree has already died, Conboy shared that the tree probably isn't worth treating. Further, if you think your tree has a chance and you want to pursue treatment, there are still cons to consider, such as how insecticide may wipe out beneficial native insects that also are feeding on your ash. You'll also need to commit to treating your tree annually or every other year to keep EAB at bay, which can be a costly investment. Even with these efforts, "it is unclear if treating the trees in perpetuity is a sustainable practice," Conboy said.

If you've decided that you want to save your tree, Andrew Conboy recommended several effective options. "These include basal trunk injections with systemic insecticides, usually administered by a tree service or plant health care service," he exclusively told House Digest. "Less commonly, you can do a soil drench/injection with insecticides as well. These are usually applied yearly or every two years, and usually cost a few hundred dollars per tree."

With the emerald ash borer already decimating tens of millions of ash trees, is it worth keeping an ash tree on your property that is currently growing well? Conboy believes it is, despite the tragic reality that many of them are no longer surviving to great heights anymore. However, many ash species are still reaching sexual maturity, which allows them to produce and spread seeds before being infected.

"I would highly encourage those with adequate space to allow any ash saplings on their property to grow," Conboy said. "Even if they get killed by the borer when they reach 5 or 6 [inches] in diameter, you will be doing your part to help preserve the local population genetics of these threatened ash species, and you will help buy time for scientists to figure out a potential solution." In other words, don't give up just yet. Continue caring for and pruning your ash tree to keep it happy and healthy, and vigilantly monitor it for signs of unwelcome guests. If you're ambitious and patient, you can even try this popular method for propagating ash trees from seed.