It seems that every year, I am called out to a town that has experienced either a tornado, violent straight-line winds, or a major ice storm which has ravaged that community's tree population. Healthy, mature shade trees now lie in mangled heaps on the ground with twisted branches, splintered wood, and tattered leaves. We are never be able to predict just when these storms are going to hit or which towns will be in the crosshairs, and so we are left to only shrug our shoulders and get to work cleaning up the mess with chainsaws and wood chippers. In other words, we can only react to the situation.
However, there's a new storm brewing on the horizon that we are fully aware of right now, and it's taking direct aim at our Ash trees: the Emerald Ash Borer (EAB). People in Michigan, Ohio, and twenty other states and Canadian provinces can attest to the bug's destructive power since its discovery in 2002 in Detroit. Once found in a community, essentially every Ash tree in town falls victim to EAB within 5 to 10 years.
This is obviously very concerning given that survey data across the state is showing that ash comprises 15 to 25 percent of all trees in the majority of Iowa towns. With recent discoveries in Waterloo and Waverly, what can we be doing now to prepare for and deal with EAB?
First, understand that Emerald Ash Borer moves in two ways: 1) natural spread, which covers just 1 to 3 miles per year; and 2) by hitch-hiking in firewood, logs, or other ash material just under the surface of the bark. Obviously, with human-aided transportation, its movement is highly accelerated and very random in distribution, which is what we now see happening across the Midwest. If we can prevent spreading EAB artificially, we can buy ourselves much more time to get ready - thus, simply do not move firewood or other Ash material out of its local area.
Second, and this might sound ironic, but the single most important action we can take now to prepare for EAB's arrival is to plant more trees. When you boil it down, EAB poses two major challenges: 1) the high costs of removing & disposing of all the dead ash trees, especially for municipalities who will have to deal with hundreds of them all at once, and 2) the acute loss of shade, energy conservation, aesthetic values, and other benefits provided by those trees.
The first issue is essentially a fiscal one - city officials may need to begin removing a percentage of their Ash trees pre-emptively, before EAB's arrival, in order to keep annual budgets in the black. But the second challenge can be overcome by any civic-minded individual with a shovel, because by planting trees now, we give those trees that much more time to grow up and become established before EAB arrives.
In fact, a prescription for any community to develop a healthy, sustainable tree population would be to establish a routine, annual quota of planting (and removing) a certain number of trees each year. This ensures a diverse mix of different sizes and ages of trees, similar to the way a well-managed company constantly recruits and trains young employees. When the veterans retire, there is an ample supply of replacements ready to move up and fill the vacancies.
In terms of species diversity, the Iowa DNR Forestry Bureau recommends aiming for no more than 10 percent of the entire tree population be comprised of a single species, and no more than 20 percent from a single genus, such as Maples or Oaks. This won't guarantee trees that live forever, but it will help dampen the impacts of another catastrophic tree pest that might come along in the future. For help in choosing alternative tree species to use in planting, please visit the Iowa Arborist Association website and look under "Resources."
But, you might ask, what about a treatment? Is there any way to save the Ash trees? In fact, there are some insecticide products that exist which can fend off an EAB attack if done preventatively. However, great caution and consideration needs to be invoked before jumping into the water headfirst. First and foremost, entomology experts and arborists generally recommend not treating trees unless you are within 15 miles of a known EAB infestation. This threshold is based on the cumulative experience of resource managers throughout Michigan, Ohio, and other infested states.
In this forester's personal opinion, any do-it-yourself "soil drench" products should be avoided altogether, along with trunk or leaf sprays. These are very easy to misapply or over-apply, have shown inconsistent results, and are often highly toxic in the environment, potentially contaminating groundwater, ponds, and streams. Some are appearing in an increasing number of studies that show great potential for harm to songbirds and honey bee populations.
Professionally-applied treatments that are injected directly into the tree by a trained arborist, such as those with the active ingredient Emamectin Benzoate, seem to be less risky to the environment, but must be done at least every other year for the rest of the tree's life. At a few hundred dollars per tree, it doesn't take an economist to realize that this could only be feasible in very limited and unique situations. The Iowa State University Extension service has a good publication on possible treatments for EAB.
Thus, there is no silver bullet, and there is no quick fix. Clearly, given the fact that we know what's on the horizon for our community's shade trees, a proactive approach is called for, rather than a reactive one. And knowing how long it takes to establish shade trees, there's no reason to delay. Let's work together to improve and sustain our community's healthy tree populations.