Nematode infestation kills over dozen trees on campus


Editor’s Note: This article was completed as an assignment for a class in the A.Q. Miller School of Journalism and Mass Communications.

When the trees on campus are changing color, it often makes for a picturesque autumn scene. When the pine trees are changing color, on the other hand, there is a problem. Due to pine wilt infections, some trees on K-State’s campus are not only turning brown, but they must also be cut down.

Pine wilt is caused by an organism called the pine wood nematode, which hitchhikes from tree to tree by way of the pine sawyer beetle. The nematode enters a tree through feeding wounds left by the sawyer beetles.

Megan Kennelly, associate professor of plant pathology, described the pine nematode as “a microscopic worm.” According to Kennelly, once nematodes occupy a tree, the infection is a fairly rapid process which results in the tree dying within a few weeks to a few months.

“The nematodes have a reproductive cycle of a few weeks. They multiply and block the water-conducting tissue in the tree,” Kennelly said. This inhibits the trees’ ability to properly absorb water and nutrients, causing the “wilting” effect. She said that eventually, “the tree turns a gray-green, then yellow and eventually brown and dies.”

Kennelly said pine wilt has been common in eastern Kansas since its arrival in 1979 and especially so this time of the year. The sawyer beetles, and thus the nematode, are inactive during the winter and only reemerge around May 1, when they once again start spreading from tree to tree. Because of this sequence of events, now is the time when a lot of the damage done by the nematode is visible.

Keith Lynch, associate professor of horticulture, forestry and recreation, said pine wilt generally affects the Scots pine in our area, but can also spread to Austrian pine. This year’s infestation has been particularly bad.

“It’s running rampant in Manhattan right now,” Lynch said. “Once the tree is infected, there is no hope.”

Because the beetles become active around the beginning of May, infected trees need to be cut down before April 1, Lynch said.

“You must cut as low to the trunk as possible and then burn or chip the wood,” Lynch said.

The Division of Facilities is responsible for controlling pine wilt. According to Joseph Myers, main campus grounds manager, 18 trees have been removed this year alone.

“Facilities services tries to remove diseased trees when they are identified,” Myers said in an email interview. “The infected trees are taken to the Riley County Transfer Station for disposal. We also try to grind the stumps of trees that have been removed.”

Once a tree is infected, there is no way to cure it and the tree must be disposed of. However, there are methods to protect trees from infection.

“There are some injections that are reasonably effective at preventing the disease, but they are expensive and you have to hire an arborist,” Lynch said.

According to Kennelly, these are “at least a couple hundred dollars and the injections have to be done again every two years.”

For these reasons, paired with the large number of pine trees on campus, this method of combating pine wilt is not an option for the facilities division.