Emerald ash borer (EAB) is an invasive beetle introduced from Asia. It entered North America from China near Detroit, Michigan, probably on wooden packing crates. It was first detected in Wisconsin in 2008. Since then, we have detected it in 51 of Wisconsin’s 72 counties. Currently, the most severe EAB damage is concentrated in the southern half of the state.  EAB attacks all species of ash trees, except mountain ash, which are not true ash trees.

Life Cycle and Damage

Adult EAB beetles are active in late spring and early summer. They lay eggs on the bark, and the larvae, which are flat and worm-like immature beetles, hatch and burrow under the bark. The larvae kill trees by feeding on the wood immediately under the bark. This disrupts the tree’s ability to carry water and nutrients up from the roots and kills the tree from the top down. 

Quarantines and Firewood

You may have heard about the EAB quarantine over the years. For 10 years, the State of Wiscosnin placed individual counties under quarantine as EAB was detected there. Now the entire state is under quarantine for EAB. 

When only some counties were quarantined, it was illegal to move some ash forest products and hardwood firewood from a quarantined county to a non-quarantined county. Because all counties are now quarantined, wood products can move more freely within the state. However, it is still illegal to move firewood and other regulated items out of state to non-quarantined areas. 

Emerald Ash Borer Insecticide Treatment Considerations

Several insecticide products are available to homeowners for control of emerald ash borer (EAB). Since the presence and infestation level of EAB is quite difficult to determine at early stages of an infestation, insecticide treatments may be merited to mitigate damage by EAB. However, not all ash trees should be treated as some may be too extensively compromised or in poor condition to receive treatment. Tree location, value, and health, as well as the cost of treatment are all factors to consider.

Due to the expense of yearly insecticide treatments, one should consider the value of a particular ash tree in relation to insecticide treatment costs before making any treatments. In addition, consider the health of each tree before treating.

Research suggests that insecticide treatments are significantly more effective on EAB-infested ash trees with less than 50% canopy thinning. Insecticide treatments are not suggested for trees with greater than 50% canopy thinning. Trees with greater than 50% canopy thinning should be removed and handled in accordance with local guidelines. 

Most of the products available to homeowners are systemic insecticides containing imidacloprid and are applied as soil drenches around the base of an ash tree. A few granular products are also available. Recent university research suggests that applications of imidacloprid should be made in spring to be most effective. For best results, treatment of trees should begin before trees become infested. Lastly, insecticide treatments must be repeated each year to maintain the health of ash trees.

Homeowners may also contact a certified arborist or certified pesticide applicator to treat their trees. Professionals have access to some products that are not available to homeowners.