How should we deal with the emerald ash borer?
Kathy and I have a number of mature trees on our lawn and in the parkings on our corner lot.
Two of the street trees are ash trees (we think).
We’re trying to decide what to do about that. Other Jefferson residents are mulling the same question.
The emerald ash borer, an invasive beetle from Asia, was first found in the United States in southern Michigan in 2002. It has spread since then into 24 states, including Iowa in 2010.
Thirteen Iowa counties, most recently Boone and Story, are now home to the insect.
The beetle’s larvae destroy ash trees.
Unless the tree is inoculated at least every other year, it will die as the borer expands its territory throughout the state.
The mature beetle lays eggs in the tree’s wood, and the hatched larvae bore S-shaped channels across the inner nutrient pathways that feed the tree, cutting off the ash’s food supply. The holes made by exiting adult beetles have a distinctive D-shape.
The tree begins to die from the crown downward, and a diseased tree will sometimes put out suckers from its trunk. An infected tree can take from four to seven years to die.
To see if a suspect ash tree is infested with ash borer larvae, remove some bark and look for the S-shaped channels in the inner wood. The adult beetle is about one-third of an inch long, and the larvae are about an inch long.
Greene County’s ISU Extension office, the city of Jefferson and the Greene County Conservation Board have all considered what response — if any — should be made to the ash borer threat.
Extension held two ash borer meetings this past April, one for elected public officials and staff, the other for the general public.
The Jefferson water and sewer committee met Aug. 8 to discuss the situation.
County conservation board director Dan Towers has given thought to how the borer is likely to affect the county’s parks.
All three entities are thinking along the same lines: decisions about ash trees will likely be made on economic factors, with inoculation a viable option at a property owner’s expense where a mature ash tree significantly enhances the property’s value.
Fortunately, ash trees are not as prevalent in Greene County as were American elms prior to the arrival of Dutch elm disease a few decades ago. So infestation by the emerald ash borer will not be as devastating as the Dutch elm fungus was.
Conservation director Towers said that ash trees are present in the county’s parks, but they do not predominate.
There are now quarantine regulations against transporting ash firewood from counties where the ash borer has been found. Some counties require labeling and bundling of firewood in their parks, Towers added.
He plans for the county conservation board to make decisions this winter about how to handle firewood issues and to put them into effect next spring.
But no attempt will be made to inoculate ash trees in Greene County parks, he said.
The cost would be prohibitive, and the expense would be ongoing. And dead trees actually provide some benefits to wildlife such as woodpeckers, owls, squirrels and other species.
County Extension director Michael Cooley said that woodpeckers, for which the emerald ash borer is a food source, can reduce the borer population about 30 percent in a given area. Some states have begun to experiment with a small, stingless wasp that kills ash borers; it can further reduce the borer count by another 20 or 30 percent.
But such natural predation can only slow the kill rate of ash trees. It can’t eliminate the threat.
Brad Riphagen, of Jefferson, local Trees Forever and Jefferson Tree Committee specialist, said that injection of an insecticide directly into the tree is the preferred method of inoculating against the emerald ash borer.
The cost, including labor and materials, ranges from $8 to $10 per inch of tree trunk diameter. The most effective insecticide, he said, should be applied every other year, in springtime.
A count by Jefferson city personnel turned up 101 ash trees in the city’s parks and cemeteries.
That doesn’t include the street parkings.
Riphagen said that an urban forester from the Iowa Department of Natural Resources will survey all public trees in Jefferson next year to get a complete count.
Current plans call for David Teeples of the city staff to remove seriously infected ash trees from city property unless they are too large, in which case they will be contracted out to a professional tree remover.
The city will undertake a program to replace trees as they are removed.
Riphagen advised that replacement tree selection be as diverse as possible, to avoid massive destruction of a single species like Dutch elm disease in future infestation situations.
Trees Forever will help with suggestions of replacement trees; Riphagen mentioned tulip trees, hackberrys, American lindens, Kentucky coffee trees, hornbeams and oaks. Consideration would need to be given to overhead power lines.
The city gives Trees Forever $2,000 a year for trees, which could be used for the replacements. Trees Forever also has access to grants that could be used.
The two ash trees on the parkings between our home’s sidewalks and the streets are 18 and 20 inches in diameter.
At $9 per inch, the total cost to inoculate them works out to about $350 every other year, or a continuous cost of $15 a month.
That’s like a large pizza with breadsticks each month.
We’ll probably spend the money to save the trees.