Pine wilt spreading misery

The veteran tree service owner couldn't help but admire the majestic Scotch pine when he drove by it on West Maple Road.

It stood tall and large, a nearly perfect shape, despite many springs of straight-line winds and pounding hail and winters of snow that might have bent or broken less-sturdy stock.

But despite how it looked, the tree in the middle of Prospect Hill Cemetery was dead. Pine wilt disease did what the weather couldn't do.

A tree that dies of pine wilt disease at this time of year is something of a drama queen. In a matter of days or a couple of weeks, it can go from appearing healthy to appearing near death. The disease doesn't suddenly take hold, but the tree's need for water increases in summer, and the disease shuts down the vascular system that transports that nourishment.

“The tree needs water, and the nematodes are inside breeding and clogging up the resin canals,” said Eric Berg, the community forestry program leader for the Nebraska Forest Service.

“Essentially, the tree bakes itself to death.”

Estimated to be 80 years old, the Prospect Hill tree, in the Elkhorn area, is one of an increasing number of Scotch and Austrian pines in eastern Nebraska being cut down and burned, buried or chipped into mulch. They are victims of the disease that first appeared near Nebraska City in the early 1990s.

Pine wilt is now appearing farther north and farther west, said Laurie Stepanek, a forest health assistant at the Nebraska Forest Service. Most cases, however, are still in the southeastern corner of Nebraska.

Stepanek conducts disease surveys — tracking where it starts and where it's most prevalent. She said Missouri was the hub for pine wilt disease when arborists first started seeing it in the early 1990s.

In Nebraska, the leading edge of the disease now is Grand Island in the central part of the state and Norfolk to the north. A few isolated cases have been reported farther west, near North Platte, Valentine and McCook.

Landscaper Jim Keepers described the look of pine wilt as faded, gray-green needles, followed by browning.

Keepers, president of Finders Keepers Landscaping in Omaha and past president of the Nebraska Arborists Association, said trees that have died because of pine wilt must be chipped, burned or buried. To prevent spreading pine wilt, diseased trees cannot be cut for lumber.

When processed by a chipper, however, the wood can be used as a mulch.

The chipping destroys the pine sawyer beetles, which carry the pinewood nematodes that cause the problem. The nematodes cannot survive without their host, the beetle.

Keepers offered these removal guidelines:

Ÿ If a tree dies between May 1 and Oct. 1, remove and destroy it immediately.

Ÿ If a tree dies after Oct. 1, remove and destroy it by April 30.

When a tree disappears from the landscape quickly, people might not realize how many others are lost, too. That worries Galen Olsberg of Galen Tree Trimming Inc.

Trees should be replaced as soon as possible, he said, and a homeowners association is providing a good example of that at 120th and Q Streets. The group is replacing diseased pines as they die with Colorado and Black Hills spruce trees, which aren't vulnerable to pine wilt.

Stepanek, of the State Forest Service, said removing a diseased tree in a group of trees may slow the progress of the disease if the pine sawyer beetles haven't already moved to other Scotch and Austrian pines. If you see bore holes in the dead or dying tree, it's a sign that the beetles have left that tree and have moved to another.

The chemical abamectin can be injected into healthy trees to keep the beetles out. However, it's not effective on diseased trees.

Six pines had to be removed from Prospect Hill Cemetery already this year, Enfield said.

“It's to the point that I drive by and give them a call. We cut them down as fast as they die.”

Fall is a good time to take out diseased trees, and it's also a good time to plant a replacement.

Conifers tend to be shallow-rooted overall with a deep tap root. Don't plant deeply, but give a new tree a site where the tap root can develop properly as the tree ages.

Conifers like good aeration but don't do well in overwatered and overfertilized yards.

Once established, conifers typically use half the water of deciduous trees. Give a conifer one-half to one inch of water every couple of weeks.

In an area that has an irrigation system, take out one of the irrigation heads, use mulch and place the tree at the edge of the yard.

Chip Murrow, a community forester assistant for the Nebraska Forest Service, recommends a native pine. In western Nebraska, the limber pine is a good choice. White pines and ponderosa pines will grow in Omaha and Lincoln, and lacebark and red pines grow in both eastern and western Nebraska.

Other good choices of conifers include spruce and fir trees.

“The thing to stress is diversity,” Keepers said. “Scotch pine was cheap, and it grew fast.”

Murrow agreed. Look no further, he said, than yesteryear's Dutch elm disease and the future loss of ash trees to the emerald ash borer.

“We've been bad about not learning from the past,” he said.

Contact the writer:

444-1059, rhonda.stansberry@owh.com

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