The Emerald Ash Borer (EAB), Agrilus planipennis, is an extremely destructive, invasive wood-boring beetle that is ravaging ash tree populations throughout North America. It is regarded as the most destructive insect pest in the 21st century. Just this past August, this metallic green invader has been confirmed in three Upstate counties of South Carolina (Greenville, Spartanburg and Oconee). The movement of this pest to our neck of the woods was inevitable as well as the subsequent attacks in the years to come to our ash trees, regardless of age, size or health condition.
The EABs native range spans across eastern Russia and northern Asia, so how in the world did it get here? Popular belief is that it was introduced into North America in ash wood used for shipping pallets and packing materials found in cargo ships and shipping containers.
It was first discovered in 2002 near Detroit, Mich. and Ontario, Canada. Since its initial attack, the EAB has spread across many eastern and mid-western states, wiping out hundreds of millions of ash trees. In 2011, it was found in Tennessee, then in North Carolina and Georgia in 2013 and now South Carolina. As of this writing, the EAB has been found in 31 states.
This menacing pest is about the size of a cooked grain of rice. The adult beetle emerges in the spring and feeds on ash leaves before laying eggs within the bark crevices. After hatching, larvae chew through bark and burrow into the phloem and cambium layers of the tree. The larvae tunnel galleries within these layers, disrupting the flow of water and nutrients and girdling the tree from the inside. As a result, tree health declines and death eventually follows.
Management of the emerald ash borer has been extremely challenging and the successful eradication of this pest is very unlikely. Still, some management strategies have shown effectiveness in slowing its spread. South Carolina is currently under a statewide quarantine for ash, which prohibits the movement of ash wood and any material derived from ash trees, into or out of South Carolina.
Other defensive management includes the use of preventative insecticides, pre-emptive removal of ash trees and biological control. Preventative insecticidal treatment of ash trees may improve resistance to infestation, but there is no guarantee to effectiveness and may be cost-prohibitive due to annual treatment costs. Removal of ash trees prior to attack is a drastic move, but may also help slow or prevent the insects spread.
Experimental biological control efforts have been in progress since 2007. Because the EAB has no natural enemies to control its population here in North America, scientists have imported four different types of non-stinging wasps from Asia. They are parasiticc in nature, laying their eggs in either the EAB eggs or larva. As the wasp eggs mature, they kill the host. Parasitic wasps are increasingly used in agricultural pest control as they themselves do little or no damage to crops. Due to the large number and long life cycle of ash trees, it may be many years before we know if the biocontrol is effective against the EAB.
Ash trees are commonly found in bottomland areas of natural forests, especially near rivers and creeks. Ash trees are also planted ornamentally in urban areas as street, park and yard trees. Thankfully, here in Camden we have a very small percentage of ash trees as we have a high tree species diversity which creates more resiliency to pests and diseases.
To prepare for the EAB, there are a few things that we can do now. First, conduct a quick inventory to determine if ash trees are present in your yard. Second, make a note of their health and monitor the tree(s) by looking for signs and symptoms of EAB presence (thinning canopy, yellowing foliage, dead twigs and small branches, profuse branch sprouting and splitting bark). Third, consider treatment or removal in the next year or two.
In an effort to raise awareness about this invasive pest, the SC Forestry Commission’s Urban & Community Forestry Program is partnering with Trees S.C. (a state-wide non-profit organization), to offer workshops to educate communities, residents and forest landowners on the EAB threat and how to manage the situation. The first workshop will be held in January in Greenville.