Towns pursue different strategies to fight ash borer infestation

Emerald ash borer

Native to Asia, the emerald ash borer was unknown in North America until June 2002, when it was discovered as the cause of ash tree deaths in southeast Michigan and parts of neighboring Ontario, Canada. Arborists think the first insects were likely contained in packing crates or materials made from ash wood and unloaded from a cargo ship, and research has shown the ash borer was infesting trees in Michigan for five to 10 years before its presence was documented in 2002.

The metallic-green insects, just a half-inch long as adults, attack only ash trees. If not properly controlled, the penny-sized pest has the potential to wipe out the ash tree species throughout North America.

The ash borer spread has been rapid. First identified in Illinois in 2006, the destructive bug is now found in 23 states ranging from New Hampshire to Colorado, as well as in two Canadian provinces. Adults can fly at least a half-mile away from the trees from which they emerge, but arborists note that many infestations begin when people move infested ash nursery trees, logs, or firewood into non-affected areas.

All native North American ash tree species — and particularly green ash and black ash — are susceptible. Damage begins when newly hatched larvae bore through the bark into the area between the bark and wood, where nutrients are transported throughout the tree. Starting at the top of tree, up to half of all branches may die in the first year of infestation, and most of the canopy will die off within two years of the time when symptoms are first apparent.

Burr Ridge has been actively dealing with the emerald ash borer since 2008, when an ash borer infestation was first spotted in the northeast corner of the community. The village promptly launched a treatment program, one of the first undertaken by any local community, to contain the infestation for as long as possible.

One aspect of this effort was a comprehensive GIS-based survey of all trees in Burr Ridge, categorized by species, genus, trunk diameter, and condition. The survey showed hat ash trees account for 2,152 of the 12,111 trees on public land in the village, or 17.8 percent. The only trees found in greater numbers were maple trees (19.9 percent).

Presented with three strategies — remove all ash trees, treat all ash trees, or treat some and remove others — officials have followed the third option, known as the “managed decline scenario.” Under this approach, the village treats only those ash trees with trunks greater than 12 inches in diameter that have been documented by an arborist as in good or excellent condition. Ash trees judged to be in poor or very poor condition, or dead, are targeted for removal. No action is taken on the remaining ash trees, which include all those in fair condition and all those with trunks less than 12 inches wide. Of the three options, the managed decline scenario offered the lowest overall cost over a 10-year period, according to the village.

“Our object is to sustain the (ash) trees that are healthy and in good condition, and control costs at the same time,” said Paul May, director of public works.

Although untreated ash trees will inevitably succumb to ash borer infestation, May said their removal will bring the village closer to its target goal of having no more than 5 percent of public trees made up of any one species.

May said a significant number of Burr Ridge residents are treating ash trees on private property, and in some cases funding the treatment of trees on public land which the village intends to leave alone. To aid this effort, Burr Ridge has loaded an “EAB Treatment Map” at www.burr-ridge.gov. Residents can plug in their address and see which ash trees will be treated and which will be left alone.

Willowbrook approach

Willowbrook officials have opted against treatment and are now pursuing a two-year program to remove and replace every ash tree on public land, including the 10 parks within the village.

“The advice we had was that treatment was not as effective as it could be,” said Garrett Hummel, Willowbrook’s management analyst.

Starting last July, the village began removing EAB-infested ash trees, and expects take down at least 250 ash trees in the first year of the program. Parkway trees are replaced with another species. Although residents can indicate a preference, the village makes the final call, and does not guarantee if the site of the removed tree is suitable for replanting.

Because diversity is a key element in maintaining a healthy urban forest environment, Willowbrook is replacing its public ash trees with 19 different species, including maples and oaks. The village’s management plan, along with a full list of approved tree species, including descriptions and photos, can be found at www.willowbrookil.org.

Darien treatment

Darien’s plan of attack has been to inject the trunks of its estimated 2,500 parkway ash trees with a pesticide known as TREE-äge (emamectin benzoate), an EPA-approved chemical that tests have shown offers the best option in protecting ash trees against the ash borer threat. The city has completed the five-month treatment effort at a cost of about $140,000, according to Daniel Gombac, director of municipal services. Even so, the pest had already taken its toll in Darien, as the city was forced to cut down those ash trees that had lost 50 percent of more of their branches, he said. Once injected, ash trees are protected against the effects of the ash borer for a two-year period.

“The city’s philosophy was that the investment required to protect the trees was worth it,” Gombac said, adding removing and replacing all 2,500 ash trees would be costly from both a financial and aesthetic viewpoint.

“We are currently re-evaluating all of the ash trees for mortality,” he said.

Gombac said residents who have ash trees on private property must take action to prevent their eventually destruction.

“We are urging residents to contact a private tree service, a certified arborist, or a similar professional, because if they take no action, they will eventually lose that tree,” he said.

Treatment options other than injections, such as soil-drenching insecticides, cost less and are fairly simple to administer. Treating ash trees before they show ash borer symptoms is the best course of action, whether the treatment calls for trunk injection, soil injection, or soil drenching.

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Emerald ash borer

Native to Asia, the emerald ash borer was unknown in North America until June 2002, when it was discovered as the cause of ash tree deaths in southeast Michigan and parts of neighboring Ontario, Canada. Arborists think the first insects were likely contained in packing crates or materials made from ash wood and unloaded from a cargo ship, and research has shown the ash borer was infesting trees in Michigan for five to 10 years before its presence was documented in 2002.

The metallic-green insects, just a half-inch long as adults, attack only ash trees. If not properly controlled, the penny-sized pest has the potential to wipe out the ash tree species throughout North America.

The ash borer spread has been rapid. First identified in Illinois in 2006, the destructive bug is now found in 23 states ranging from New Hampshire to Colorado, as well as in two Canadian provinces. Adults can fly at least a half-mile away from the trees from which they emerge, but arborists note that many infestations begin when people move infested ash nursery trees, logs, or firewood into non-affected areas.

All native North American ash tree species — and particularly green ash and black ash — are susceptible. Damage begins when newly hatched larvae bore through the bark into the area between the bark and wood, where nutrients are transported throughout the tree. Starting at the top of tree, up to half of all branches may die in the first year of infestation, and most of the canopy will die off within two years of the time when symptoms are first apparent.

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