Dutch elm disease claimed more trees in 2005 than any year in recent memory according to Riverside Village Forester Michael Collins in his annual report on tree mortality presented last night to village trustees. With 87 trees succumbing to Dutch elm last year, the disease was the No. 1 tree killer in Riverside and accounted for 55 percent of all trees lost in the village during 2005.

In all, Riverside lost 126 trees from public areas of the village, including parkways and public parks. Of the trees killed by Dutch elm, 56 were on public land and 31 were on private property.

In his report, Collins said the spike in Dutch elm is “directly associated to the drought stress many plants experienced throughout the year” and that his department’s “aggressive approach to monitoring and removal of infected elms may also explain higher mortality rate based on responsiveness.”

In addition to cutting down infected trees to prevent the disease spreading to healthy elms, Collins had 23 healthy elms ranging in diameter from 10 to 36 inches injected to protect them from becoming infected. He estimated that it cost roughly $500 to inject a 20-inch diameter elm.

But it’s extremely unlikely that Riverside will be able to do any kind of large-scale elm injections to protect all of the roughly 550 remaining elm trees in the village. Collins reported that injecting the elms would cost roughly $135,000 per year on a five-year rotation for a total cost of $675,000.

“Based on current budget constraints,” Collins wrote, “this preventative strategy is not a realistic approach.”

Injections on a small scale will continue, said Collins, targeting both young and older elm trees. Managing Dutch elm in Riverside will continue to “remain a significant expenditure” for the Forestry Division of the village’s Public Works Department.

“You want to protect [younger trees] so that 100 or 80 years from now, you’ll still have the specimen alive in Riverside,” said Collins in an interview Monday.”

On alert for insect pests
In addition to Dutch elm disease, Collins said two insects were of specific concern in Riverside. And although neither of the insects has done any visible damage to Riverside trees, Collins and his staff are working to get the word out on gypsy moths and the emerald ash borer.

While no trees died as a result of gypsy moth infestation, the insect has found a home in the south end of the village, particularly in the First Division.

The gypsy moth, according to Collins’ report, is a European import that has become “one of the most destructive pests of hardwood forests in the United States.” When caterpillars hatch during spring months, they feed on tree leaves. In some severe cases, caterpillars can defoliate entire trees.

Collins added that the Cook County Forest Preserve District reported gypsy moths near Riverside in the late 1970s, but that they appear to have arrived in Riverside more recently. While most common in the south end of the village, some moths were discovered in the central part of the village in 2005.

Collins said his staff discovered 30 gypsy moth egg masses in trees along Scottswood Common and in Indian Gardens. The egg masses were removed and burlap sacks were wrapped around trees to trap caterpillars.

“It’s impossible to eradicate gypsy moths completely,” Collins said. “There are no natural controls. What you try to do is mitigate the problem. Overall there is great potential for them to move [to other areas]. But by doing a combination of activities, you can contain it.”

While the gypsy moth could become a problem in the future, Collins said he was very concerned about the emerald ash borer, an insect native to China that has wreaked destruction in parts of Canada, Michigan and Indiana.

“Once that insect comes through here, it’ll be devastating,” Collins said. “The main thing is getting the word out about the ash borer. People can’t be bringing back firewood from Michigan and Indiana.”

Storms: No. 2 killer
After Dutch elm disease, the biggest cause of tree removals in Riverside was storm damage. Some 30 trees were removed following storms in 2005, while another 28 were lost due to the severe drought during last summer.

But while, 126 trees were lost last year, some 90 were planted as part of the village’s ongoing tree replacement program.