Since the Polar Vortex subsided, there has been quite a bit of buzz about the Emerald Ash Borer (EAB), an exotic beetle that is killing ash trees across Indiana and the U.S., being killed by the multi-day sub-zero temperatures we experienced here in Indiana and elsewhere. Some recent research (the full paper can be accessed USDA Forest Service, Cold Hardiness of Emerald Ash Borer, Agrilus Planipennis: A New Perspective) predicts that when EAB larvae reach 0°F, 5% will die; at -10°F, 34% will die; at -20°F, 79% will die; and at -30°F, 98% will die. Based on some -15°F temperatures here at the Purdue West Lafayette campus, we might expect around 50% of the EAB will die, but some additional points need to be considered.

An adult emerald ash borer feeds off a leaf. (Purdue University Department of Entomology photo/John Obermeyer)

EAB larvae are located overwinter under the bark in infested ash trees, so the bark may offer some insulation. Snow is also an excellent insulator, so the lower trunk of ash trees in deep snow or drifts may not get as cold as ambient air temperatures. Some trees in town or near structures may remain warmer due to heat radiating or escaping from buildings. The message is, unfortunately, that the cold weather we experienced was probably not enough to solve our EAB problems.

It is good news that some of the population was probably killed by the cold weather, leaving fewer larvae to damage ash trees next spring. This will be a temporary setback for the borer, since one of the biological strengths of insects is their capacity to reproduce and grow populations quickly. Further north in places like Minnesota, the news for the ash trees may be better where temperatures below -30°F may have killed most of the larvae, providing some additional time to prepare for the EAB onslaught. Here in Indiana, we need to continue to monitor, prepare and act to limit the damage EAB will do.

Some basic steps include:

• Don’t move firewood – Firewood can harbor EAB and several other serious tree pests and spread them to new areas.
• Learn to identify ash trees, EAB and the symptoms of EAB damage.
• Learn about EAB control techniques.
• Learn how to decide if your ash tree should be treated with insecticide to protect it from EAB or removed and possibly replaced with another tree species.
• Work with your neighbors to monitor and manage the ash trees in your area.

Purdue Extension offers science-based recommendations to help you manage the EAB threat at Emerald Ash Borer in Indiana.

Resources:
New Hope for Fighting Ash Borer, Got Nature? Purdue Extension-FNR
Invasive Pest Species: Tools for Staging and Managing EAB in the Urban Forest, Got Nature?
Emerald Ash Borer Cost Calculator – Purdue Extension Entomology
Planting Your Tree Part 1: Choosing Your Tree, Purdue Extension YouTube Channel
Tree Planting Part 2: Planting a Tree, Purdue Extension – Forestry and Natural Resources YouTube Channel
Indiana Invasive Plant List, Indiana Invasive Species Council, Purdue Entomology
Landscape Report Shares Importance of Soil Testing, Purdue FNR Extension
Find an Arborist website, Trees are Good, International Society of Arboriculture (ISA)
Tree Risk Management – The Education Store, Purdue Extension’s resource center

Lenny Farlee, Extension Forester
Hardwood Tree Improvement and Regeneration Center (HTIRC)
Forestry and Natural Resources, Purdue University