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What is Emerald Ash Borer (EAB)?

Emerald Ash Borer (EAB) is a non-native invasive insect pest first reported in Michigan in 2002 and it has since spread to 30 states and is responsible for killing millions of ash trees. EAB attacks all species of ash and generally kills the trees within 3-5 years.

EAB was confirmed in Boulder in 2013, and has since spread to Gunbarrel in 2015, Longmont in 2016 and Lafayette in 2017. The spread is expected to continue into the Denver Metro area including Westminster within the next 1 to 3 years.

Introduction and spread of EAB will likely be from the careless movement of ash firewood, lumber or nursery stock containing the developing stages of the insect.

It is difficult to detect new infestations of EAB. The insect has usually been in the tree for 2-3 years before symptoms are visible.

Signs of an EAB infestation include:

  • branches without leaves, especially at the tops of ash trees
  • vertical splits in the bark exposing S-shaped tunnels
  • wild leafy branches (new growth) sprouting from the trunk
  •  D-shaped exit holes

The symptoms of EAB are similar to other insect and abiotic problems. Ash trees have struggled in the last several years from drought conditions, the late freezes and the commonly found lilac ash borer. Lilac ash borer is a native insect that has attacked ash trees for many years and frequently kills branches in the tree and sometimes the entire tree.

A quarantine has been in place on Boulder County, the Town of Erie and the adjacent landfills restricting the movement of ash firewood, logs and nursery stock. It is illegal to move ash firewood or other products from the quarantine area. There is little to no enforcement of the quarantine with public education as the primary means to get the word out.

Further information can be found at the following links: 

Colorado Department of Agriculture website

Colorado State Forest Service Quick Guide 

How do I tell if I have an Ash Tree?

Green ash, white ash,and Autumn Purple ash are very desirable for landscape planting because they grow well under difficult conditions and have been widely planted. There are an estimated 69,000 ash trees in Westminster. Use this identification key to determine if you have an ash. The EAB/Ash Tree ID app can be downloaded by searching in app stores for “ash trees”.

This smart phone app is available to help determine if it is an ash tree: Ash Tree App

What should I do?

Survey your property for the number, size and location of ash trees. Determine if the tree is worth saving. Is the tree healthy, in a good location, and with minimal prior injuries? View the Managing EAB Decision Guide 

Treat the ash trees you want to preserve. EAB is expected to be found in other areas of the Denver Metro area including Westminster within 3 years. It is more cost effective to preventatively treat the tree than to remove and replace a dead tree.

There are preventative pesticide applications that can be given to protect ash trees.  The most effective, environmentally-safe pesticide is emamectin benzoate, which is injected into the trunk of the tree by a certified pesticide applicator. It is effective for 2 and possibly 3 years and the approximate cost of an application is $150 for an average sized tree in Westminster. Imidacloprid is a pesticide available to homeowners under several trade names and can be applied as a soil drench. It is less expensive, but the effectiveness is inconsistent and may be up to 60% and care must be taken when applying to avoid killing pollinators and other animals. There are pesticide options available for treating EAB

Plant replacement trees in existing empty planting spaces. This will lessen the impact from the future loss of ash trees. Consider planting new trees under existing ash trees so they can become established before the ash trees are removed. Plant replacement trees after the removal of ash trees. Use a broad diversity of tree species when planting to avoid monocultures that can be destroyed by pests like EAB and Dutch Elm Disease. See our list of recommended replacement tree species 

Remove ash trees that are not candidates for preservation treatments. Once EAB is fully established, all ash trees that have not received preservation treatments will be killed. It will be more expensive and more dangerous to remove ash trees after they have been dead more than two years. It is highly recommended to hire a qualified arborist to safely remove trees.

See the following links for more information.  EAB Colorado CSU Quick Guide

What is the city doing?

View The City of Westminster’s EAB Action Plan

Westminster has participated in EAB trapping surveys for the past 5 years along with the U.S. Department of Agriculture, Animal and Plant Health Inspection Service, Colorado Department of Agriculture and the Colorado State Forest Service.

Our inventory of ash trees has been updated with the location, condition and size to help prioritize which trees are candidates for preservation treatments. The city has 1,700 ash trees of which 1,200 are recommended for preservation.

Forty unhealthy ash trees have been removed by mid-year 2017 as we go through our rotational pruning.

By mid-year 2017, 75 new trees have been planted in existing empty planting spaces to mitigate the future loss of ash trees.

205 ash trees were treated in 2017 by our Forestry staff with emamectin benzoate. One third of the ash trees the city wants to preserve will be treated each year and placed on a three-year rotation.

Why should we care?

There are an estimated 69,000 ash trees in Westminster, comprising about 13 percent of the tree canopy. One out of every seven trees is an ash with a collective appraised value of $69 million. The loss of these trees will decrease property values in Westminster by $2.8 million as the attractiveness of our businesses and homes decline.

If all 69,000 ash trees were removed, the cost would be $21 million with replacement costs of $28 million. The loss of the ash tree canopy will increase storm runoff, increase erosion and decrease water quality. The loss of shade will increase air temperatures, increase energy consumption and increase irrigation water usage.