Emerald ash borer to cost Chicago-area homeowners, arborists say

The emerald ash borer has killed 25 million ash trees in Michigan since it was discovered there in 2002 and arborists in the Chicago area are bracing for similar losses as the invasive insect spreads.

Besides Michigan, the destructive pest has turned up in Canada, Ohio, Indiana and Illinois in the past four years.

Chicago is surrounded by suburbs that have reported infestations, and 18 Illinois counties are considered to be infested areas. Evanston, directly to the north of Chicago, cut down 800 infested trees this spring.

Winnetka, Elgin and Hazelcrest all have confirmed infestations. They are only three of the more than 11 Illinois cities to get hit by the destructive pest.

"[Homeowners] are going to get hit. Unfortunately with ash trees it’s like with Dutch Elm disease. It’s going to cost you one way or another," said Rex Bastian, vice president of field education at The Care of Trees, a Chicago-based arborist company.

Ash trees within fifteen miles of a known infestation are at a heightened risk of being infested with the emerald ash borer, states the University of Illinois Extension. This leaves homeowners two options: treat or remove.

"People need to make a decision about their ash trees," said Bastian, who has a doctorate in entomology, adding that homeowners should not expect their ash trees to be spared from the onslaught of the emerald ash borer.

By law, homeowners with a confirmed infestation of emerald ash borer on their property must attempt to save the tree using pesticide treatments or have the tree removed. Treatment can fail, removal of large trees can reach into the thousands of dollars, and there are several different factors homeowners should consider before deciding what to do.

Preventive pesticide treatments are homeowners’ best bet if they have trees they wish to save. However, it may not be worth it to treat small or misshapen ash trees. For his part, Bastian has decided not to treat the ash trees on his property. He lives 20 miles from the nearest known infestation and expects the emerald ash borer to eventually kill his trees.

The city of Chicago has so far been spared, but it will get hit by the emerald ash borer sooner rather than later, said John Lough, senior forester with the city of Chicago.

"We would have to be extremely fortunate to not have it in the city yet," Lough said. The Chicago Bureau of Forestry has been actively looking for emerald ash borer infestations. The planting of public ash trees was banned in 2003 to prevent the spread of the insect.

The ash tree is one of the most numerous tree species in Chicago, according to the Chicago Bureau of Forestry, with 97,000 ash trees, or about 19 percent of the total tree population in public parks and parkways. There are approximately 500,000 ash trees on private property.

And though trees can live for years after being infested with the emerald ash borer, they will die if left untreated. Arborists say homeowners would be wise to plan now for its eventual arrival.

Options for Homeowners

Pesticide treatment works best as a preventive measure. Once a tree is noticeably infested it is usually too late to save it, although a tree that is 10 percent to 30 percent infested can sometimes be successfully treated.

Ash trees can live with an emerald ash borer infestation for several years before they start exhibiting symptoms. One of the first signs of infestation is unusual woodpecker activity in the canopy of the tree. The woodpeckers target larva feeding on the zylem of the tree. The feeding of the larva impedes the tree's ability to move nutrients, eventually killing the tree.

Other symptoms of infestation include canopy dieback, vertical splits in the bark and shoots growing from the base of the tree. Once these symptoms become obvious the tree is usually in a state of irreversible decline and cannot be saved by pesticide treatments.

Property owners should decide whether or not to treat their trees before they are faced with an infestation. For instance, a property owner may decide to administer preventative treatments to large, healthy ash trees but may not treat small or sickly ash trees.

A certified arborist can help homeowners determine what application technique is most appropriate. Trees absorb pesticides the fastest when applied with a trunk injection. This invasive technique is most appropriate when the tree is at risk of an imminent infestation.

Less invasive techniques are slower to be absorbed by the tree and are appropriate in less urgent situations. One technique is to inject the soil at the base of at-risk ash trees with pesticides. Soil injects are administered by professionals, but over-the-counter treatments are also available.

Areas of the tree that have died off due to infestation are not going to spring back, and even if a tree survives treatment it could be disfigured from the infestation.

"Understand that it may not work. The tree may die or look bad," said Rex Bastian, vice president of field education at The Care of Trees, a Chicago-based arborist company.

If treatment is successful homeowners could be spared from having to remove and replace the tree. Removal can potentially reach into the thousands of dollars, with costs determined by the size, condition and location of the tree.