Emerald Ash Borer

City of Brentwood Emerald Ash Borer Plan


The City of Brentwood has been working on a plan to reduce the impact of the Emerald Ash Borer (EAB). With 260 Ash trees – over 8% of the City’s Urban Forest – the EAB will have a devastating impact on the City of Brentwood. The City is proactively using resources to manage this invasive pest while analyzing the impact on the tree canopy and ensuring public safety. The City has developed an EAB Plan that addresses the public environmental and economic needs and seeks to distribute the costs associated with the loss of tree canopy over a manageable timeline.

The Insect

The Emerald Ash Borer, an insect native to Asia, has been responsible for the death of over 100 million Ash trees in the United States and Canada. The adult EAB is about one-half-inch long and metallic green in color. The insect was first discovered in North America in 2002 near Detroit, Michigan. It is believed the EAB was accidentally introduced to America in wooden shipping materials. The EAB has decimated Ash tree populations in the Great Lakes region, and now infestations have spread into 30 states and two Canadian provinces.

How the Damage is Done

During the summer and fall, the Emerald Ash Borer larvae feed and develop in an Ash tree’s vascular tissue, the layer within the bark where sap moves. This disrupts the tree’s ability to transport water and nutrients. Unlike other trees – such as Oak or Elm, which remain relatively stable after they die – Ash trees lose moisture internally very quickly and begin to fall apart soon after they die. EAB affects all native Ash trees. EAB infection and mortality is extremely predictable and consistent – essentially, every Ash tree is killed.

Local Impact

Emerald Ash Borer was discovered in Missouri in May 2015 in St. Charles County. The pest was found in St. Louis that same month by a utility contract crew working for Ameren in the area near Calvary Cemetery. It is estimated that by 2025-2030, the Ash tree mortality rate in our region will approach 100%. By that time, the local Ash tree population will be in a state of hazardous decline.

Chemical Treatment: Not a Good Option for Brentwood

Brentwood Parks & Recreation is not using chemical treatment as an EAB-management option because of the relatively small number and low quality of the Ash in our City.

Also, EAB populations will wane after the initial mass mortality from chemical treatment, but it is unlikely they will ever disappear. This means treatment may needed indefinitely. Continually introducing the required, non-selective insecticides into the environment could have disastrous unintended effects, including killing beneficial insects along with the EAB.

The Plan

Brentwood Parks & Recreation Department’s recommendation is to remove every publicly owned Ash tree in the City of Brentwood by the end of 2022. This should put the City ahead of the Ash-mortality curve and allow staff flexibility for unforeseen setbacks.

The plan prioritizes public safety first and the loss of tree canopy second. Ash tree removals will be planned to lessen the overall impact of canopy loss. All trees will be replaced. The scope of this project will be immense.

During the reforestation process, the City’s Urban Forester will focus on a biologically diverse planting schedule. Maintaining biological diversity will help reduce future impacts from invasive species in all replacement locations. When replanting, staff will concentrate on the following:

  • Areas with good remaining canopy will be replanted according to normal procedures.
  • Areas where Ash tree removals have a drastic effect on canopy will be replanted with an emphasis on trees with a faster growth rate. These species will be inter-planted with slower growing trees such as Oak, Beech and Dogwood.