By the early 1970s, after Dutch elm disease had mostly finished its decades-long run in Champaign-Urbana, less than 50 of the more than 14,000 elms in the community were left standing.
Some residents, sometimes tearfully, still recall street sides, parks and other green spaces, once shaded by stately elms, reduced to fields of dead stumps.
Now, University of Illinois researchers and state and federal officials are warning that another invader has the potential to take an elm disease-like toll on ash trees here and elsewhere in the state.
An outbreak of the emerald ash borer beetle was first noticed a year ago in Detroit area. It has killed an estimated 6 million trees and left 13 Michigan counties quarantined, along with some areas of Canada and Ohio, making it illegal to export ash trees and products and firewood of any kind.
Still, officials worry that the half-inch-long green beetle could make its way to Illinois on wood, especially firewood, unwittingly imported from Michigan, or even clinging to the gear of returning travelers.
It may be in the state already, though none has been seen yet. Researchers think the emerald ash borer was actually in Michigan for five to 10 years before it reached the critical mass that made it noticeable.
"We were absolutely shocked at what we saw," said James Appleby, a UI entomologist who visited the Detroit area last month to view the damage. "You'd go down some of the streets, and rows of ash trees were all dead."
"What that fungal disease caused to the elm, this could be an analogy for what (the emerald ash borer) could do to ash," said Appleby, a UI natural resources and environmental sciences professor and a scientist with the Illinois Natural History Survey.
The emerald ash borer also has the potential to be a much bigger problem than the Asian longhorned beetle, which threatened hardwood trees like maple, polar and willow in the Chicago area beginning in the late 1990s but has been largely quashed with an aggressive program of removing infected trees.
"This is a real serious pest," said Kenneth Kruse, a scientist with the U.S. Agriculture De-partment Animal and Plant Health Inspection Service in Illinois. "It spreads fast. It's a lot faster moving than the Asian longhorned beetle. You gotta find it quickly."
The ash borer is smaller than the Asian longhorned, as are its telltale bore holes, making it more difficult to spot, he said.
In addition, it tends to kill trees faster – in a couple years for a small tree – because of the way it does its damage.
Adult ash borers lay eggs on the bark or in crevices. The larvae that hatch then bore be-neath the surface and feed on layers containing a tree's circulation system. Eventually, they cut off the movement of nutrients, and the tree dies.
"They're not eating a huge amount of wood, but they're eating it in the worst possible place," said Charles Helm. A UI-based entomologist with the Illinois Natural History Survey, he's working with Appleby, Kruse and the state Department of Agriculture on a response plan to monitor for and repel the invader.
"Once a tree is infested," Kruse said, "there's no way you can treat that tree other than cutting it down."
While scientists aren't sure, the emerald ash borer, like the longhorned an Asian import, may have arrived via the Great Lakes in wooden pallets and other lumber used for shipping from China.
"These things can harbor living insects," Helm said.
The beetle would find the same kind of accommodating feeding and breeding environment in Illinois as it found in Michigan.
Ash trees make up about 9 percent of the forest trees in the state, more than 177 million trees in all. That doesn't count the millions of ash trees in public and private green spaces and in tree nurseries.
"We have a great number," said Appleby, who has been training Illinois foresters to look for the beetle. "It's a very popular ornamental tree. It's a tree that does fairly well in urban areas, and that's why it's planted."
A quick survey by the Morton Arboretum pegged ash trees as 10 percent to 30 percent of the tree stock in parts of the Chicago area, which Helm said already is being monitored for the emerald ash borer.
The numbers in East Central Illinois communities are comparable, local officials said.
"Until real recently, ash trees were definitely one of the top recommendations for street trees," said Paul Sermersheim, Danville's community improvement coordinator.
Steve Lane, Danville's parks and public property superintendent, said he probably won't be planting new ash trees for now.
Likewise, Champaign City Forester Bill Vander Weit and Urbana Arborist Mike Brunk have pretty much stopped planting ash, although not only be-cause of the emerald ash borer.
Nonetheless, Champaign's street trees are about 10 percent ash, nearly 19,000 trees in all. Urbana has about 900 of the trees along its streets, about 7 percent of its street tree population.
Brunk and Vander Weit said ash trees also have been popular with local homeowners and contractors, in part because they do well where soil has been disturbed by construction, and they grow fast.
"White ash has been used heavily in our new subdivisions," Vander Weit said.
Brunk figures there may be seven or eight times as many ash trees on private property in Urbana as there are on city streets.
Vander Weit and Brunk said they had already cut back on planting ash because green ash trees in particular tend to age poorly, sometimes shedding large, dangerous limbs. The trees also have been afflicted in recent years by a microbial disease called ash yellows and other pests and suffered from the area's weather swings.
But the biggest reason for the cutback is that Champaign and Urbana started to have too many ash trees. The cities try to keep any one species at about 10 percent of the tree population.
That's a direct vestige of the Dutch elm disease experience and a reason the community is better positioned today to weather a storm like the emerald ash borer.
"That will help us in any disease or insect infestation situation," Brunk said.
What, where to look for emerald ash borer
Officials say help from Illinois residents will be vital in identifying, and responding quickly to, any outbreak of the emerald ash borer here. Among the signs to look for:
– Dead foliage in the upper third to half of ash trees, an early sign of infestation.
– The beetles and their larvae. Adult beetles are about a half-inch long with metallic-looking dark green wings and a brass-colored to golden-green body. Larvae are creamy white to light green, can reach more than an inch in length and have a 10-segmented abdomen with brown pincers on the last segment.
– Bore holes made by adult beetles to emerge from under the bark after they've developed. The holes are about 1/8th inch in diameter and have a distinctive D shape. They're generally found on large branches and trunks.
– A maze of S-shaped channels under the bark from larvae feeding.
– Ash sprouts around the base of a dead or nearly dead tree, from the root system trying to save itself.
For more information, see www.na.fs.fed.us/spfo/eab/index.html .
You can reach Greg Kline at (217) 351-5215 or via e-mail at firstname.lastname@example.org .