Small Insects, Big Problems
Emerald Ash Borer was discovered to be the cause of the widespread decline of Ash trees in Southeast Michigan in 2002. It is believed the insect was transported from Asia in solid wood packing shipping crates sometime in the 1990s, and it took several years for the insect population to build to noticeable levels. Since its discovery, the Emerald Ash Borer has spread to several other states, as well as Canada, and has killed millions of Ash trees.
Adult Emerald Ash Borers feed on the foliage of Ash trees with minimal impact on the trees. The larvae, however, feed in the cambium layer of Ash trees, which disrupts the movement of water and nutrients throughout the tree. Once the infestation reaches a certain level, the Ash tree will be killed.
Trees Attacked by Emerald Ash Borer
Emerald Ash Borer has only attacked Ash trees in North America. The insect has shown a preference to certain Ash species. Black Ash and Green Ash are among the most preferred species, while the Blue Ash and White Ash are among the less preferred species. Nonetheless, once the population of Emerald Ash Borer builds up in an area, all Ash species are eventually attacked by this insect.
Symptoms of Emerald Ash Borer Infestation
- Increased wood pecker activity on Ash trees. Woodpeckers will create jagged holes in the bark and the bark they pull off the tree can be found on the ground around the tree.
- Vertical bark splits will develop over the feeding galleries. Sometimes the feeding gallery can be seen through the split bark.
- D-shaped exit holes can be found on branches, the main trunk, or on large root flares.
- Epicormic sprouts may develop on the lower trunk or shoot up from the base of the tree trunk.
- As the Emerald Ash Borer infestation continues. the foliage may wilt. Branches will decline and then die back completely. The canopy may become thinner on one part of the tree, or the entire canopy may become gradually thinner.
Although stressed trees are the initial victims of Emerald Ash Borer when they first move into an area, the insect will eventually begin to attack any healthy Ash trees greater than 1 inch in diameter.
How to Control the Emerald Ash Borer
Arborists have been able to use multiple methods to save Ash trees from being killed by Emerald Ash Borer. Control treatments for Emerald Ash Borer may be sprayed on the tree, injected into the tree, or soil injected/soil drenched around the base of the tree trunk. Scientists are also working on biological controls for Emerald Ash Borer.
Trunk injections can be done from just before leaf out until the end of the growing season. Some trunk injected insecticides provide control of Emerald Ash Borer for more than one year.
Soil injections or soil drenches are ideally done in the early spring, but can be done anytime there is adequate soil moisture. The tree does require several weeks to absorb and transfer the soil injected insecticides. Spraying of the tree, especially the tree trunk, can be done once the beetles have emerged and are mating. In the upper Midwest Emerald Ash borer starts emerging from Ash trees in May or early June. Spray treatments to control Emerald Ash borer are designed to prevent newly hatched larvae from entering the Ash tree. Multiple treatments may be necessary to achieve adequate control.
Scientists have tested and released Three tiny, stinger-less wasps native to China.
- Oobius Wasp
- Tetrastichus Wasp
- Spathius Wasp
Oobius attack Emerald Ash Borer Eggs, while Tetrastichus attacks Emerald Ash Borer Larvae. Extensive testing has shown that these Three wasp species only attack Emerald Ash Borer. The initial release of these wasps has been done in Michigan and Minnesota, however last year they were released in Northern Illinois.