August 26, 2015

Pest Alert: Emerald Green Borer Arrives, Threatens Princeton’s Ash Trees

Pest Alert

Princeton is known for its many tree-lined streets. The municipality earned Tree City USA status almost 20 years ago from the Arbor Day Foundation. Today, some of those trees are being threatened by a small invasive beetle, the Emerald Ash Borer (EAB).

Princeton’s Shade Tree Commission and Lorraine Konopka, the municipal arborist, have been keeping a close eye on the spread of this dangerous new pest in Princeton. The EAB may look rather innocuous in the stock photo shown here but the non-native has already killed tens of millions of Ash trees in the United States. First discovered in Michigan in 2002, EABs have since been found to have infested 23 other states and two Canadian provinces.

Ash trees have compound leaves with five to eleven leaflets, the bark on older trees has a ridged diamond-shaped pattern while younger trees are smoother. Each seed case has an oar shaped wing in bunches that are delightful to watch as they whirligig toward the ground.

Found last year, 2014, in four communities in Somerset, Mercer, and Burlington Counties, the EAB is highly destructive and can kill all species of Ash.

“This small green insect, accidentally introduced to our continent from Asia, probably in wooden packing crates, has been spreading outward from its original introduction in the Detroit area, killing hundreds of millions of ash trees,” said local environmentalist and blogger Steve Hiltner, adding that the insect is likely to spread across Princeton over the next few years.

According to Mr. Hiltner, the beetle was found in Princeton in a trap set by Ms. Konopka out along River Road. “All ash trees that haven’t been treated with an herbicide, usually injected in springtime, are at risk,” noted Mr. Hiltner, “but treatment can provide protection for several years. Of the various chemicals available, I’ve heard the most praise go to Arbor Mectin; Tree-Age has a similar formulation,” he said.

Mayor Liz Lempert’s monthly newsletter also warns of the danger to Princeton’s trees. She noted that Princeton maintains a database of all municipal street trees with information about age, type, and health; the tree inventory database can be used to learn the species of a particular tree or to check on the status of neighborhood trees.

As reported by the mayor, Princeton’s Shade Tree Commission offers advice for those seeking to protect Ash trees on their property. To identify an Ash tree, visit:

To monitor your Ash trees for the EAB, look for dying branches at the top of the tree, woodpecker damage, galleries under the bark, d-shaped holes, bark splits, sprouting at tree base and along trunk, and green adult beetles.

The websites of the New Jersey Department of Environmental Protection (NJDEP) State Forestry Services ( and the New Jersey Department of Agriculture (NJDA) offer useful information on the life cycle of the insect, the signs and symptoms to look for, and management strategies.

According to the NJDEP State Forestry Services website, “You will know when the risk of mortality becomes urgent,” from the above mentioned signs.

The beetles may also be found in woodpiles by using “purple prism” traps.

One way to avoid spreading the infestation is to avoid moving firewood. The Shade Tree Commission advises using only locally sourced or certified firewood. “Visitors who bring infested firewood to second homes or campgrounds near you put your trees at risk,” stated the NJDEP website.

Shade Tree Commission meetings are generally held on the fourth Tuesday of the month at 5:30 pm in Monument Hall; the next meeting will take place September 29, at 5:30 pm. For more information, visit: