What is EAB?
The Emerald Ash Borer, Agrilus planipennis, (EAB) was first detected in the United States in 2002 near Detroit, Michigan. Since then it has spread rapidly, currently inhabiting most eastern states and moving as far west as Colorado. It has been detected in all states bordering Vermont, including Quebec. This pest has devastated ash trees throughout this area, killing millions of trees and costing millions of dollars.
The adult EAB is a small metallic green beetle, about a half inch long. In North America they are known to attack all 16 native species of ash (Fraxinus) and the white fringetree (Chionanthus virginicus). They generally infest only ash, not other tree species. The adults feed on the leaves of the trees during their short 3-week lifespan. During this time they can mate several times and deposit about 60 to 90 eggs on the bark of ash trees. The eggs soon hatch and the larvae burrow through the bark and into the cambium. There they feed on the phloem and outer xylem forming S-shaped galleries. The larvae overwinter in the inner bark or outer sapwood before emerging as adults in the early summer. This feeding is very disruptive to the trees vascular system, blocking nutrition and water transport, causing canopy dieback and decline of trees. Trees can be killed within 2 years if heavily infested. The rapid rate of reproduction of EAB can lead to high population levels in a few years following the initial infestation.
EAB Signs and Symptoms
Early detection of EAB in newly infected trees is difficult, particularly for the general public because newly infested trees exhibit minimal visible external symptoms in the early stage of infection until EAB populations build in an area. It can take several years to detect an EAB infestation after it arrives, when the first trees begin to die. The first symptoms of EAB are cracks in the bark where the larvae have been feeding within the tree.
As populations build, woodpeckers can be seen attacking infested trees in search of the larvae. Woodpecker foraging signs are highly visible and a frequent identifying feature, though usually occur only once EAB is well established. The general health of infested trees decline rapidly, exhibiting obvious signs of canopy thinning and dieback and epicormic sprouts (water sprouts). The D-shaped emergence holes made by adults are small and hard to detect when infestations are light, but are a reliable sign of attack as populations build.
Above: Signs of EAB in ash trees: tree with thinning canopy and epicormic growth at the base, larval tunnels under the bark, D-shaped exit hole.
Burlington’s public urban forest is extremely vulnerable to this pest. Based on our street tree inventory, as of February 27, 2015, there are 1,275 ash trees along our streets and within our parks, which represents 11% of our forest resource. This does not include those growing in woodland habitats, such as forested parkland or areas along the bike path. Inventory-generated information indicates that 43% of the ash are within the 13-18 inch DBH (Diameter Breast High) range, and 92% are ranked as either good or fair condition. Most are in a vigorous stage of life, and are at a size that provides substantial benefits to our city. Ash Trees have not been planted in Burlington since EAB was discovered in the US. There are 1,014 ash growing along the streets, 42 in cemeteries, and 219 growing in parks.
Table 1: Percentage and number of ash trees in Burlington public urban forest by diameter class
|Diameter class (in.)||Percentage||Number of trees|
|36 – 42||0.3||4|
Some neighborhoods or streets have higher proportions of ash than others and would be especially hard hit by this pest (Fig. 3). Ash trees grow throughout the city as single trees or as groves. The loss of this genus would cause a reduction of canopy coverage and necessitate the planting of over 1,000 young trees. The resulting new forest would be younger, and in some locations all new trees. The current locations of ash trees are shown below in blue.
|Table 2. Streets or Parks with Significant Ash Populations|
|1,2,3,5,6||Old North End, Downtown, South End||Oakbeach Dr., Southwind Dr., Scarff Ave., Ferguson Ave., Charlotte St., Lower Battery St., S. Winooski Ave. (south of Adams), College St. (upper), Main St. (upper, by UVM green), Crombie St., George St., East Ave., Grove St., Hillside Dr., Hildred Dr., Mansfield Ave., Loomis St., Greene St., N. Union St., Hyde St., Perkins Pier.|
|4,7||New North End||Morrill Dr., Stirling Place, Hope St., Lori Ln., Sandra Cir., Appletree Point Rd., Cumberland Rd., Edinborough Dr., Westminster Dr., Nottingham Ln., Valade St., Clover Ln., North Beach|
Monitoring and Early Detection
USDA has implemented a national monitoring plan. Summer monitoring in 2015 will be conducted primarily with purple prism traps in 20,000 sites nationwide. The locations are selected based on proximity to current outbreaks and a high probability of EAB detection. We will rely on this federal monitoring effort to keep us informed of the spread of EAB.
Based on existing information on the life cycle of EAB, emergence in Vermont would likely occur in early June, which may be the time when ash tree inspection could begin. Currently we monitor firewood at North Beach campground and hand out educational materials on EAB to all campers.
EAB is a fast spreading pest which is considered unstoppable, and will inevitably reach Vermont within the next 5 years. We must be prepared for its inevitable arrival in Burlington. Multiple management options and a general management plan are discussed below.
- Inventory Ash Trees: This has been completed. We now have a searchable database overlaid on GIS maps allowing for quick site locating and work scheduling.
- Monitoring and Detection: Though EAB has not yet been found in Vermont, it may be here already. Currently ash trees in Burlington are inspected during routine maintenance by city Parks personnel, who have received training regarding symptoms of EAB. Tree care activities are conducted across all areas of the city on a regular basis. We intend to develop a schedule for inspecting ash trees in various locations, particularly in areas that are less frequently visited for management. We will also investigate opportunities to initiate an early detection program in collaboration with local volunteer groups.
- Chemical Treatment: Once EAB has been detected in an area, ash trees usually die within 3-4 years, or sooner. Therefore, prompt action is needed to either remove the infested trees or initiate a chemical treatment for those not infected. Current recommendations say to wait until the borer is within 15 miles before beginning a chemical regiment. Chemical treatment of infested trees does not guarantee survival. Treatment efficacy depends on many factors, including the severity of infestation, the length of time that the tree has been infested, the age of the tree and its health condition, and the type of pesticide used. Not all public trees will or should be treated with pesticides. Ash trees of poor quality or in the poor or very poor health condition classes will be removed. High quality ash in fair or good condition classes that provide the most benefit to the city (in terms of shade, water retention, aesthetics, etc.) will be considered for pesticide treatment. Although chemical treatment can be expensive, time consuming over a long duration, and require the use of insecticides, it will allow neighborhoods to retain trees and the benefits they provide until trees of other genera can become established.
Four methods are commonly used to apply insecticides to ash; each with advantages and disadvantages.
Trunk injection: By using the trunk injection method, the chemical is injected directly into the sapwood for systemic uptake. It takes 1-2 weeks for the chemical to be distributed throughout the tree. There is no direct chemical exposure to the air or soil. Most US municipalities use this method to treat infested trees.
Soil injection or soil drench: The soil injection/drench method places the chemical into the soil surrounding the base of the tree. The tree roots absorb and take up the material and distribute it throughout the tree in 4-6 weeks.
Lower trunk spray: The lower trunk spray method places the chemical directly on the bark of the tree to be absorbed. It is faster than soil application because the chemical is more water soluble. The chemical is exposed to the air during and after application.
Cover spray: Cover sprays can only be used for a few weeks when the adult insect is out of the tree. This method involves spraying the entire tree with the chemical.
Four insecticides are registered to manage EAB: Imidicloprid, Dinotefuran, Azadirachtin and Emamectin benzoate. Each insecticide is manufactured by and sold under different brand names.
Estimated treatment costs (including labor of Parks Department personnel):
Soil Drench: $ 0.67/inch DBH
Trunk Spray: $1.60-5.00/inch DBH ($3.30/inch DBH in calculations)
Tree Injection: $5/inch DBH
The average DBH (Diameter Breast High) of our ash trees is 13.58 inches. The estimated cost to treat different percentages of Burlington’s public ash resource ranges from $580 – $64,930, depending on how many trees are treated and the type of treatment used. This expense would recur because insecticide treatments must be repeated annually or every 2 years. There are also environmental costs associated with long term pesticide treatment that are difficult to quantify. In addition, some specialists recommend initiating treatment for highly prized tree before infestation has been detected.
|Table 3. Treatment cost ($) by application method and percentage of tees treated (per application)|
Decisions on whether to treat or remove infested trees will need to be made on a case by case basis. Trees will be rated based on their value and identified as worth treating or removing by Parks employees in the Trees and Greenways division. This should be completed as soon as possible to prepare for projected costs. This will reduce a rush to judgement when pest pressure arrives. For trees selected for treatment, the method of treatment will dictate how many trees can be treated, depending on the availability of funds to support treatment. However, given the high cost of treatment, it will not be financially viable over the long term. Chemical treatment will help the city transition to a forest with few ash, but will not allow ash trees to be financially or environmentally viable as a large percentage of our trees in the foreseeable future.
If chemical treatment is selected as an option, we suggest using the trunk injection method. Although the most expensive, it provides the greatest protection over a longer time period while reducing the amount of chemical exposure to the environment. The cost per inch of several injectable pesticides by brand name is listed below in cost per inch of DBH: Xytect (imidacloprid) $0.27, Tree-Age (emamectin benzoate) $1.69, Ima-jet (imidacloprid) $1.20, Azasol/Treeazin (azadirachtan) $0.90, Imicide (imidacloprid) $0.96. These prices account for only the purchase price of the pesticide. The toxicity of each of these pesticides on pollinators varies and is affected by the time of application, flowering, and if pollinators are present. Emamectin benzoate, imidacloprid, and dinetofuran are believed to have similar levels of toxicity to bees while azadirachtin is less toxic to bees. To summarize on chemical treatment: we would favor the use of azadirachtin, imidacloprid or emamectin benzoate as a trunk injection.
- Removal: Ash trees lose structural stability rapidly after death by EAB. The wood dries and the brittle tree falls apart. Dead and heavily infected trees will need to be removed promptly. Removal of infected trees may reduce the rate at which the insect spreads. Tree removal costs vary depending on tree size, site limitations (utilities, other targets, access), travel time, and wood loading and hauling. Some cost estimates are presented based on average tree size and removal time. The actual cost per tree will vary greatly, but figures presented below allow for budgetary planning.
Calculations used for cost estimates (based on current operating costs provided by the City Arborist):
3-Person Crew with Bucket Truck and Chip Truck: $180/hour
Average Tree Size: 13.58 inches
Average Removal Time per Tree: 2 hrs.
|Table 4. Removal cost based on percentage of Burlington’s public ash trees removed|
- Stump Grinding: After the dead trees are removed we will need to make space for new trees in our greenbelts by grinding out the stumps. This involves grinding the stump out with a machine, hauling away the grindings, and refilling the hole with soil.
3 Person Crew with Stump Grinder, Tractor, and 2 Trucks: $205/hr.
Average Stump Size: 14 inches
Average Stump Removal Time: 30 minutes
|Table 5. Stump removal cost by percentage of stumps removed|
- Replanting: There will be extensive planting opportunities following an outbreak of EAB. Although the trees will be small, it will be possible to increase our species diversity.
New trees will be of 2” caliper, with a wholesale price of $200, costing $600 dollars to install and water for one year.
|Table 6. Tree replanting cost by percentage replaced|
The cost to replant trees will exceed that of removing and grinding the stumps. Not every ash tree removed will need to be replaced as not all are in ideal growing locations. A rate of 90 to 80% replanting is the most likely outcome. The planting will be accomplished as fast as the budget allows.
- Wood Utilization and Disposal: There will be a large quantity of wood chips and chunks available after EAB strikes. We have a wood fired generating station, the McNeil Station, in our community, to make good use of this while destroying insect larvae. There is a national quarantine to limit the spread of EAB. Firewood and ash tree products cannot be moved from inside the quarantined area to areas outside the infestation. It is currently legal to repurpose infested ash trees and products if they stay within the quarantined area. Due to the high volume of ash wood that will be available uses other than electric generation could be considered.
Cost Estimate Options
Remove All Ash Trees, Grind Stumps, Replant: $1,354,688
Trunk Inject 25% of Ash, Remove 75 % of Trees, Grind Stumps, Replant: $1,037,661 (first year)
Trunk Inject 50% of Ash, Remove 50% of Trees, Grind Stumps, Replant: $720,629 (first year)
Soil Drench 75% of Ash, Remove 25% of Trees, Grind Stumps, Replant: $347,372 (first year)
Considering the following factors: existing tree condition ratings, implications of long term chemical use, benefits of existing trees, large upfront cost of numerous tree removals, and citizen desire for tree lined streets; when examined as a whole this information indicates the following as a potential plan for Burlington’s urban forest:
Chemically treat 50-75% of ash with injection at an estimated cost of $43,285 to $64,930
Remove 25-50% of ash, grind stumps, replant at an estimated cost of $338,672 to $677,344
Budget additionally for chemical injections every two years of $43,285 to $64,930
The total cost for this plan is $720,628 to $403,602 upfront with additional expenditures every two years. Increased chemical treatment will reduce initial expense, but will create an ongoing maintenance budget concern.
The trees in Burlington provide many benefits, filtering the air, giving shade, keeping us cool, reducing storm water runoff, creating wildlife habitat, and improving the view, just to name a few. The loss of ash trees without replacement would result in an 11% reduction in these benefits. A coordinated multidimensional approach is needed to be prepared to help the urban forest recover after this pest arrives.
Many people have heard of EAB since its first US discovery in 2002, but not everyone will be aware of the exact impacts it will have on their community. This plan, or developments that arise after EAB discovery, will be made available to the public. Outreach in ash-heavy neighborhoods will be accomplished with door hangers or flyers detailing what this means for that particular street. This will be accompanied by information available from the Department’s website and Facebook account.
The forecast may look a little grim, but the forest will recover. If we get discouraged, it is only necessary to remember the Dutch elm disease outbreak of the last century.
Private Property Ash Trees
If you have an ash tree on your property, please consider one of the following:
1.Treat. If you have not yet considered a treatment program, please contact an ISA Certified Arborist to assess whether your tree is suitable for treatment. Treating in June or July is preferred to minimize damage. Once EAB has been detected within 15 miles of the property treatment should begin.
2. Remove. Dead and dying trees become high risk for public safety. Remove and replace untreated ash trees with a different species. Doing nothing may put you, your property, and public safety at risk.
Where to view more information regarding the EAB?
Who to contact if I have any questions?
Forest Pest First Detectors
There are 147 volunteers statewide to answer any questions or to confirm EAB identification. A list of First Detectors is available here: http://www.vtinvasives.org/first-detectors. Burlington’s First Detectors include Brian Sullivan (email@example.com, 802-862-8245), Gus Goodwin (Gustave.firstname.lastname@example.org, 715-225-8814), and Rhonda Mace (email@example.com, 802-777-8698).
An observation of EAB can also be reported online at http://www.vtinvasives.org/eab-photo-submission-form or by phone at 1-866-322-4512. Additional questions can be directed to Elise Schadler at firstname.lastname@example.org or at 802-656-2657.
Burlington Parks, Recreation, and Waterfront
Contact city arborist Vincent “VJ” Comai, at email@example.com