Common name: Emerald ash borer
Scientific name: Agrilus planipennis
Hosts: Ash (Fraxinus species). All 16 native ash species are susceptible to attack. In northeastern Illinois, common susceptible ash species include green ash (Fraxinus pennsylvanica), white ash (F. americana), blue ash (F. quadrangulata), and black ash (F. nigra). Horticultural cultivars of these species are also susceptible. Healthy ash trees of any size are vulnerable to attack. Emerald ash borer does not attack mountain-ash, prickly-ash, or wafer-ash since they are not true ash or Fraxinus species.
The emerald ash borer (EAB) is a serious pest of ash trees. EAB has been found in a large portion of the United States and Canada. It was found in Illinois in 2006 and has killed millions of ash trees since that time.
While adult emerald ash borer (EAB) may feed on ash leaves, it is the larvae that do the real damage. The larvae tunnel under the bark in the water-conducting tissue, cutting off the water supply. This leads to dieback of limbs, first in the top of the tree. As the damage under the bark continues, dieback of limbs increases and the whole crown may decline. Cracks can form in the bark and expose the serpentine galleries made by the larvae. In later stages of decline, suckers, known as epicormic shoots, may form low on the trunk. Woodpecker damage can be another sign of EAB infestation, as woodpeckers will try to get at the larvae to eat them. While many wood-boring insects are drawn to stressed or dying trees, EAB will attack healthy trees. This invasive pest is so aggressive that trees may die within two to four years after they become infested.
Emerald ash borer (EAB) overwinters as larvae in feeding galleries under the bark. These larvae pupate into adults in spring (usually April and May). The adult beetles chew their way out of the tree and emerge. The emergence hole is shaped like a capital ‘D.’ Not all adults emerge at the same time and adult emergence can occur over several weeks, peaking during June. The adults are a metallic-emerald green in color, with elongated bodies about ½ inch long.
After emerging, the adults will feed on leaves and begin to mate. Egg-laying begins about three to four weeks after emergence. Eggs are laid in cracks and crevices in the bark and hatch into small larvae within a couple of weeks. The larva is white to cream in color, with an elongated and segmented body. The head is slightly darker than the body and is flattened. The larvae feed in the food-conducting tissues (phloem) under the bark, but will also tunnel in the water-conducting tissue (xylem), leading to disruption in the water supply for the tree. Their tunnels are serpentine (S-shaped).
There are limited ways to manage emerald ash borer (EAB) culturally. Removal and destruction of infested trees that will not benefit from chemical treatment can help reduce the spread of the insect. Avoid moving firewood. Firewood can contain the larvae of EAB, as well as other unwanted pests. Buy firewood on site when camping.
Some parasitic insects are being studied as possible management tools for EAB. Studies are ongoing.
Insecticides are available to manage EAB. There are insecticides for home use which can be drenched into the soil. Professional arborists have insecticides that they can apply through tree injections, trunk sprays, or soil injection.
For more information, contact The Morton Arboretum Plant Clinic (630-719-2424 or firstname.lastname@example.org).