Earlier this summer, an invasive species biologist spotted the dreaded emerald ash borer (EAB) in a town just west of Portland, Oregon while examining some ash trees that looked unhealthy. He reported it to local authorities, who soon confirmed his identification.  

Although it looks like a harmless and beautiful iridescent green insect, EAB has earned the title of the most destructive invasive pest. It was first found stateside in Michigan in 2002, likely arriving in wooden pallets from overseas. Since then, it has devastated forests and ecosystems in other parts of the country, but the West escaped unscathed for decades due to the physical barrier presented by the Rocky Mountains.  

Now that EAB has made its way to the West Coast, California’s riparian and urban forests are at risk. 

What to know 

Emerald ash borer has the potential to devastate not only common urban ash trees, but also California’s olive industry and riparian ecosystems that depend on shade from our native Oregon ash trees. Vulnerable species that are common in the Sacramento region include:  

• Raywood ash 
• Modesto ash 
• Oregon ash 
• Shamel ash 
• Moraine ash 
• Olives (both fruiting and fruitless varieties) 
• Fringe trees 

Adult borers are about ½” long and metallic green. They feed on ash leaves and bore into the wood to lay eggs, where their larvae tunnel under the tree’s bark. This tunneling slowly cuts off the tree’s transport system for water and nutrients, eventually killing an infested tree within 1-4 years.  

Although the insect itself might be hard to spot, visible signs of infestation include canopy dieback, 1/8” D-shaped holes in the bark, woodpecker activity, bark splitting, and shoots growing from the roots or trunk.  

What you can do 

• Don’t move firewood – larvae can hide under the bark. Buy it where you burn it.  
• Respect local and statewide quarantines that prohibit moving wood, logs, or live trees from areas with active infestations. 
• Learn what types of trees grow around your home, and inspect vulnerable trees monthly for signs of infestation. 
• If you see possible signs of EAB, report it to the USDA at 866-322-4512 or online. 
• If you are concerned about the health of your tree or interested in options for proactive maintenance, hire a certified arborist to inspect your trees and make recommendations. 

There are some pesticide applications property owners can pursue to protect otherwise healthy trees in areas of active infestation (California does not yet have any known active infestations). Authorities at federal, state, and local levels have implemented various measures to control spread of EAB, including quarantines, biological controls (releasing insects that prey on EAB), preventative treatments, and proactive removals of unhealthy trees. Additionally, there are efforts underway to preserve ash stock in seed banks and to identify varieties that are resistant to EAB for future reforestation projects.