The invasive emerald ash borer, a small, metallic-green beetle native to Asia, may eliminate the ash tree from North America.
In Missouri, EAB is present in 89 counties and the city of St. Louis.
University of Missouri Extension entomologist Kevin Rice explains that EAB is capable of eliminating all ash trees from our forests and cities, just like the Dutch elm disease which killed native American elms.
“This makes it one of the most serious threats now facing North American forests,” said Rice.
The EAB beetle spreads to new areas by hitchhiking on firewood transported by humans. The larvae feed under the bark of ash trees, cutting off the tree’s circulatory system. After the larvae’s infestation, tree death results within a few years.
In an attempt to successfully reduce EAB populations, Rice and his team are investigating if parasitoid wasps which attack the EAB larvae can save the decline of ash trees.
The parasitoid wasps were released in Missouri three years ago, and Rice’s team have been monitoring various field sites across Missouri, Iowa and Minnesota.
Rice explains that the declining ash tree population can cause irreversible damage to ecosystems if action is not taken.
“There's what we call cascading events, and it's sort of like dominoes. In some forests in the United States, 70% of the trees are ash and if you remove those trees, within two years, that's a huge disturbance to the ecosystem,” said Rice. That affects bird species that eat on Ash, or provide bird cover, it affects butterflies, ground beetles, and even the water cycling.”
If ash trees continue to disappear it will also result in the reduction of forest floor coverage, allowing more light to penetrate the surface.
“What we found is that then these invasive weeds explode, it's basically changing the trajectory of forest succession so these are no longer forests, they become invasive weed Meadows,” said Rice. “And that obviously has effects on mammals and birds and everything that lives in the forest.”
Ash trees are responsible for the production of everyday items like baseball bats and home furniture, and they are also one of the most common street trees.
The problem is that EAB is very effective at killing ash trees. Healthy trees can actually die from
Emerald Ash Borer within two years, and because of that trees need to be removed,” said Rice.“Removing trees from streets lined with them requires a lot of money because houses are next to them, so it is actually the most expensive invasive insect currently.”
Rice says to avoid additional infestation tree owners should watch for signs of dead branches, especially in the upper third of the tree as well as D-shaped exit holes in the bark, increased by the activity of woodpeckers, which might mean larvae are under the bark.
Rice says that trees can also be protected with insecticides before they experience 40% dieback, but treatments will need to be administered every few years.
Additionally, homeowners can apply an insecticide soil drench, available at big box stores. Insecticides must be applied long-term and are not effective on trees 20 inches DBH (diameter at breast height) or larger, however injections by an arborist are far more effective.