As the Minnesota State Fair grounds begin to bustle with activity, fair officials and University tree pathologists are trying to determine why half of the elm trees on the grounds are infected with Dutch elm disease.

About 35 elm trees have been removed from the fairgrounds so far this year, and officials said a total of 94 could be removed before the season’s end. The trees’ loss sparked controversy over the disease’s treatment and control.

“If you look proportionately at the fairgrounds compared to the Twin Cities, we have a lot more elms and that is because we take such good care of them,” said Danyl Zamber, a State Fair spokeswoman. “They are one of our most valuable assets.”

Bob Blanchette, a plant pathology professor at the University, said the disease has spread so far so quickly because the fairgrounds staff is not removing infected trees quickly enough.

“(The fairgrounds) have a large number of elms and if there are dead elms around, they will produce bark beetles and they will emerge and infect new trees,” Blanchette said. “This means the trees were not removed fast enough, otherwise they wouldn’t have had the problem.”

Fairgrounds officials have taken measures to protect their elm trees by removing the diseased trees as soon as they are diagnosed as untreatable, Zamber said.

Leben McCormick, a certified arborist for Rainbow TreeCare, said the fair has done everything it can to prevent the problem.

“They had committed to treating trees before there was an epidemic and along the way it blew up in their face,” McCormick said. “The problem is being very highly managed, but they are still having unprecedented rates.”

In 2003, the fair hired Rainbow TreeCare to take over the treating of elm trees on the grounds. State Fair staff members had taken on the task after ending a previous contract with a tree inspector in 2001.

“The first year there was one pocket of disease,” McCormick said.

When inspectors came back the next spring for an evaluation, signs of the disease were found on an “alarming amount of the trees,” McCormick said.

“Normal disease rate is 3 percent to 5 percent of elms in any one year, but we had 40 percent of our trees that had some sign of disease in them,” McCormick said.

A contracted company on the St. Paul campus could also be a cause of the problem, McCormick said.

McCormick said he had seen large piles of tree trunks at the site, which he said is not allowed.

“These trunks could likely be the cause of the beetles infecting the trees,” he said.

Blanchette said the company does chip wood, but does not accept diseased elm. The company was not available for comment.

While fair officials continue to cut down elms, new trees are being planted, Zamber said.