Orange spray paint signifies death for some stately elm trees on the University campus this summer.

The cause is Dutch elm disease, an ailment with a notorious history in the Twin Cities.

In 1977, 31,000 elm trees died in Minneapolis because of the disease, which is transmitted by bark beetles and the trees’ root systems.

“Over 95 percent of the trees on all the streets in Minneapolis and St. Paul before the epidemic were elm,” said Jim Herman, manager of the forestry program at Minneapolis Park and Recreation Board.

Today 16 percent of street trees in Minneapolis are elm, he said.

Although the epidemic is over, experts agree that Dutch elm disease is still a major concern in the Twin Cities.

The University, with about 300 elm trees on its Twin Cities campus, has protected some trees against the disease with injections since the early 1990s.

“If we sat down and crunched all the data, at least 45 or 46 percent of the elms (on campus) are under chemical protection,” said Eric Gilsrud, University campus arborist.

Fifty-eight of the chemically protected elm trees are injected with the fungicide Arbortect, a chemical agent that frustrates the growth of the disease-causing fungus.

Mark Stennes, a plant pathologist from Top Notch Treecare, researched Arbortect while at graduate school in the University’s plant pathology department.

When Dutch elm disease hits, a tree reacts with defense mechanisms, Stennes said.

One defensive response uses tyloses structures, something Stennes said are similar to balloons.

Attempting to stop the fungus distribution, the tree will fill its water-transporting tissue, or xylem, with the balloon structures like a roadblock.

If the fungus passes the roadblock, then the first signs of Dutch elm disease – yellowing leaves and defoliation – might begin.

“The truth is, trees recover all the time because of their defenses,” Stennes said. “They work a lot more than they don’t.”

Stennes said Dutch elm disease is effective because it divides fungus cells. Arbortect doesn’t let the fungus cells divide.

“It sits on the fungus like an 800-pound gorilla; that’s how Arbortect works,” Stennes said.

Problems with Arbortect

Arbortect is not without problems, though.

The active ingredient is a powder that does not dissolve in water. To make it transportable through the tree, it is boiled in acid.

Living wood cells often die because Arbortect is hard on trees at the injection site, Stennes said.

In 1996, Stennes switched to using Alamo because it is easier on the elm trees.

The University uses Alamo to treat all elm trees that aren’t under Arbortect’s protection. But treated or not, in recent weeks there has been a rise in elm deaths on campus.

Some chemically protected elms have contracted Dutch elm disease, raising questions about the validity of fungicides.

University land care supervisor Doug Lauer said he believes the fungicide treatment is generally effective.

Until the scientific community has an explanation for the recent rise in elm deaths, the University plans to stick with the current program of injecting elm trees every third year, Lauer said.

Costly alternative

Injections for elm trees aren’t easy on the pocketbook.

Stennes estimated that an Alamo injection for a very large elm tree with a diameter of 3.5 feet at breast height could cost about $565.

Despite the injection cost, University forest resources professor Gary Johnson vaccinates a city elm at his curbside every three years.

“I think that if people would look at their trees the same as every other investment they have made – the house, the car, the motorcycle – then it does require maintenance,” Johnson said.

Consulting arborist Ken Simons estimates tree values. Depending on its size, location and condition, Simons said a tree can be worth a lot of money, especially if it is in good condition and important to the landscape.

“I did one (tree), a huge oak, that had a value of $13,000,” Simons said.

Other solutions

But experts such as Stennes and Herman said controlling Dutch elm disease should not hinge on chemical injections.

Instead, both said public education on Dutch elm disease, routine property inspections for diseased elms, and proper removal and sanitation methods can make all the difference.

“It’s more a political problem than a biological problem. If we were more effective at finding the diseased trees and getting rid of them, we wouldn’t have to punch expensive holes in our trees.” Stennes said.