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Are You Prepared to Manage EAB?

Although it hasn’t been in the news on a regular basis since being discovered in Minnesota in 2009, emerald ash borer (EAB; Agrilus planipennis) continues to be a serious threat to Minnesota’s ash trees.  Last week (2/12/13) some of the leading researchers and practitioners in EAB management came to the Twin Cities to present and discuss the latest information about EAB and the management of this destructive, exotic pest.

The Emerald Ash Borer Symposium took place at the Hopkins Center for the Arts in downtown Hopkins, MN, and was hosted by Rainbow Treecare.  The progression of an EAB infestation, the myths of EAB management, what works and what doesn’t work for managing EAB, the case for conserving ash trees in urban forests, the unfortunate realities of an EAB infestation, the economics of EAB management, and the environmental impacts of the systemic insecticides used to control EAB were the primary topics covered and the symposium concluded with a question and answer based panel discussion.

The presenters included Dan Herms (Ohio State University, Department of Entomology), Chad Tinkel (Superintendent of Forestry Operations & City Arborist, Fort Wayne, Indiana), Rich Hauer (University of Wiscionsin – Stevens Point, Urban Forestry), Richard Cowles (Connecticut Agricultural Experiment Station), and Shawn Bernick (Vice President, Rainbow Scientific) and the symposium was moderated by Gary Johnson (University of Minnesota, Department of Forest Resources).  It was an impressive group with significant experience working with EAB and the presentations were informative, timely, and science-based.

Key points:

  • In general, if ash trees in EAB infested areas aren’t treated they will die; even healthy trees are attacked and can be killed in 1-3 years in areas with high infestations.
  • New EAB infestations will grow slowly at first (Minnesota today), but will ultimately increase exponentially over time until most trees are killed; after the crash, beetle populations will decrease but will likely remain active at low levels.
  • Thinning of the canopy is the first symptom and trees typically die within 2-3 years after the first symptoms are observed.
  •  Mortality rates as high as 99.7% for ash trees greater than 1” in diameter have been reported in EAB infested areas.
  • Without human assistance, new EAB infestations tend to move about a quarter mile/year when infestations are low and the rate of spread increases as beetle populations increase; when infestations are high, infestations can expand at a rate of 15 miles/year.
  • EAB management options include doing nothing (not recommended), removal after trees die, preemptive removal of all ash trees, preemptive removal with or without replacement, targeted removal with or without replacement, targeted and sustained treatment with insecticides, or a combination of tactics; all things considered relative to economics and the benefits of healthy ash trees, research supports treatment to delay and prevent mortality.
  • Ideally, municipalities should have an EAB management plan in place before EAB arrives; where ash trees have been widely planted, which is the case in most municipalities, the economic impact of EAB will be enormous and planning is a must if devastated budgets and liabilities associated with significant numbers of standing, dead trees are to be avoided.
  • At minimum, EAB management plans should include a solid tree inventory, a thoughtful treatment strategy, funding and budgeting considerations, written specifications for treatment, removal, and replacement activities, attention to politics and support from elected officials and the public, education and public awareness, plans for debris management and disposal, a risk management assessment, and an ongoing re-evaluation and update strategy.
  • Without a plan, an EAB infestation can decimate budgets and delay other important tree management activities like maintenance pruning; fewer trees can lead to decreased budgets and reduced funding which can be difficult to replace.
  • Once killed, the structural integrity of ash trees declines rapidly; trees quickly become a hazard and a significant liability.
  • The idea that the removal of ash trees slows the spread of EAB is a myth; research indicates removing ash trees actually accelerates the spread of EAB as the beetles disperse looking for host trees.
  • Ash trees have value in community landscapes on many levels – aesthetics, property values, ecological services; protecting these values is justified based on the cost of managing EAB with systemic insecticides compared to the benefits lost if ash trees are simply allowed to die; also most of the benefits provided by trees are associated with older, larger trees and it takes many years for these benefits to be realized as a result of replanting.
  • From an aesthetic, economic, and ecological services perspective, healthy, high-value ash trees should be targeted for protection while those that are not in good condition should probably be removed; healthy, older trees that have larger canopies tend to have more value than young trees with small canopies.
  • The systemic insecticides imidacloprid, emamectin benzoate, and dinotefuran have all been shown to be very effective in saving trees and have proven to be effective even on large trees under heavy pressure.
  • Ash trees can be protected over the long term with systemic insecticides or they can simply be used to delay mortality and spread mortality out over many years to avoid a crisis environment and to help maintain budgets and manage costs.
  • Imidacloprid can be applied as a soil drench or soil injected just under the surface of the soil; imidacloprid can also be injected into the trunk; dinotefuran can also be applied as a soil drench or applied as a bark spray from the base of the trunk to a height of about five feet (easy, quick, and effective); emamectin benzoate is trunk injected; imidacloprid and dinotefuran must be applied annually; emamectin benzoate is effective for two years.
  • Insecticide treatments applied in the spring work best; fall treatments can work, but are less effective; insecticides must be taken up and translocated (mid April to Mid May; trees must be leafed-out) throughout the tree by the time eggs hatch and the larvae begin to feed in June.
  • Biocontrol continues to be investigated, but doesn’t look promising; American species of ash planted in China are quickly decimated by EAB.
  • In general, infected trees with up to 20% thinning of the canopy can be saved even with high levels of infestation; too late once canopy thinning has reached 30-40%.
  • Screening of ash trees for EAB resistance has been initiated at Ohio State University and remains a hope for the future.
  • Leaching of neonicotinoid insecticides (imidacloprid and dinotefuran) into groundwater has been suggested as a concern associated with the use of these insecticides; if properly applied to as a drench to soils with an organic content of 2% or more imidacloprid has not been observed to leach more than a few inches and groundwater contamination is unlikely; injection deeper into the soil should be avoided; although immobilization through binding with organic matter is reduced for dinotefuran compared to imidacloprid, it can be applied as a basal trunk spray where it is absorbed rapidly.
  • Neonicotinoid insecticides are toxic to bees and applications to species that are attractive to pollinators should be avoided; ash trees are wind pollinated and are not attractive to bees and other pollinators; application as a bark spray to avoid uptake by non-target species that are visited by pollinators is recommended over soil drenches where such species are present.
  • Specific to concerns about the involvement of neonicotinoid insecticides in honey bee Colony Collapse Disorder (CCD), research indicates neonicotinoid insecticides are not the cause of CCD.
  • Be optimistic and be proactive rather than reactive; with careful planning, EAB can be managed, and budgets and the benefits of trees can be maintained; effective tools are available and research continues to provide new information about EAB and its management.
  • Finally, and we should have learned this lesson long ago, diversity is a key factor in the management of forest resources and should be a guiding principle when replacing ash trees lost to EAB.

To keep current on the latest science related to EAB, visit http://www.emeraldashborer.info.  This is the go-to source for the most up-to-date information about EAB.  The site includes links to a variety of EAB resources and a number of archived, on-demand webinars offered through the Emerald Ash Borer University program; new webinars are also posted and offered on a regular basis.

To comment on this research update, suggest research topics of interest, or pass along a piece of research-based information that might be of interest to your industry colleagues, please email us at Research@MNLA.biz.




Photo Credit: Jim Calkins
Figure 1. A green ash in winter; although overplanted and not always fully appreciated, ash trees are a valuable component of urban and community forests and native forest ecosystems and provide significant year-round benefits.