Emerald Ash Borer, Agrillus planipennis
Emerald ash borer is an invasive pest of ash trees. Larvae of this pest feed beneath the bark, eventually killing the tree. Emerald ash borer was found in Boulder, CO in 2013 and is actively spreading.
Description and Life Cycle
The emerald ash borer (EAB) is a flat-headed beetle. The adult is a dark metallic green beetle, about 0.37-0.5 inches long. The larvae are cream-colored with bell-shaped body segments and can reach 1.5 inches when fully grown. Larvae are the destructive stage of this insect. After hatching from eggs deposited in the bark of ash trees, larvae bore into the cambial layer just beneath the bark. Larvae wind back and forth as they feed, creating distinct S-shaped tunnels, or “galleries”. The larvae will feed beneath the bark for a year before pupating and emerging as adults in late May through July. Adult beetles create a D-shaped exit hole in the bark as they chew their way out of the tree. EAB adults typically live three to six weeks and fly up to a half-mile from where they emerge to find a new host tree. After mating, female beetles will lay 60-90 eggs, one at a time, in the crevices of ash tree bark. Distribution of this pest over long distances is possible due to the transportation of infested firewood, logs, nursery stock or other wood.
EAB tunneling on an ash with bark removed.
Steven Katovich, Bugwood.org.
EAB damage on an ash tree.
Pennsylvania Department of Conservation and Natural Resources – Forestry, Bugwood.org.
Debbie Miller, USDA Forest Service, Bugwood.org.
Adult Emerald Ash Borers and the characteristic D-shaped exit hole.
- Emerald ash borer is a green flat-headed beetle that develops in ash trees (Fraxinus spp).
- It is an invasive insect that is native to Asia. It was first detected in Detroit in 2002 and was found in Boulder, CO, in September 2013.
- Emerald ash borer wounds ash trees by tunneling under the bark. When wounds become extensive, trees show symptoms of decline and, ultimately, are usually killed.
- Systemic insecticides are typically applied as either soil drenches, trunk sprays or direct injections into the trunk, and can suppress early emerald ash borer infestations.
Injury to plants occurs as the white grubs feed on roots, which causes drought stress due to the root loss. In severe infestations turf roots are so severely pruned that areas of the lawn can be lifted or peeled back easily, as if it had been newly laid sod. Lawn areas can be killed by these injuries. The presence of white grubs in lawns is also attractive to raccoons and skunks, which will dig up lawns in search of grubs, often causing more damage than produced by the insects alone.
Lawns that are mowed at a higher level produce plants with larger root systems, which are better able to tolerate root pruning injuries. Watering practices can have variable effects. Irrigation that promotes deep root growth can allow lawns to better tolerate grub injuries. Maintaining good soil moisture in late summer and early autumn can help lawns recover from damage that has occurred. Conversely, lawns where soil moisture is kept high during the period when eggs are laid will tend to be more favorable to white grubs. Since the eggs and young grubs are sensitive to drying lawns that have some periodic drying will reduce their survival. This is particularly true for Japanese beetle.
White grubs can be killed by certain kinds of insect parasitic nematodes. These are tiny roundworms that develop within susceptible insects, eventually killing them. Several kinds of these nematodes are sold and those in the genus Heterorhabditis are effective for control of white grubs; Heterorhabditis bacteriophora is the primary nematode species used for white grub control. Grubs that are successfully attacked by these organisms turn a reddish-brown color and die within a few days. Insect parasitic nematodes will be unable to infect insects if soils are not warm enough (50° F minimum) for them to be active.
There are several insecticides that can provide very good control of white grubs when applied at the proper time. Since younger stages of grubs are much more effectively controlled than are large, older grubs, insecticides are best used in high concentration in the root zone at the same time eggs are hatching and young white grubs are present.
Insecticides applied to lawn areas can be a hazard to pollinating insects if there are dandelions, clovers or flowering plants mixed with the turfgrasses in the treated area. To reduce this risk lawns should be mowed to remove all blooms before applying the insecticides.