Nebraska Forest Service expert discovers pine wilt treatment

Mark Harrell, Nebraska Forest Service forest health program leader, initiated a project to determine whether a trunk injection aimed at controlling the pinewood nematode that causes pine wilt would be effective in preventing the spread of pine wilt.

"In 2001, I tested abamectin, an insecticide that is known to have some effect against nematodes and found that it could kill the pinewood nematode at a concentration that was feasible to use in trees," Harrell said. "I began testing it in trees later that year."

Arbor Systems, an Omaha-based company that specializes in tree injections, provided the product and the injection equipment. The company added Greyhound, abamectin's trade name, to its product line in the mid-1990s. It commonly is used to control elm leaf beetles, lace bugs, leaf miners and mites.

Greyhound is injected into the tree's trunk near the ground. Trees are given a series of injections at four-inch intervals around the tree.

Research trials were conducted in several windbreaks in southeast Nebraska in 2001 and 2002. These windbreaks were evaluated for one year. In 2003, a three-year trial was begun at Horning State Farm near Plattsmouth. The results of the Plattsmouth test showed that Greyhound, applied at six times the recommended label rate, provided approximately 70 percent protection from pine wilt for three years. Greyhound only is effective if no symptoms of pine wilt are present in the tree, Harrell said.

Due to its high application rate, Greyhound treatments are expensive, he said. The product also must be applied by a trained arborist.

"Treating a tree with a trunk diameter of 10 inches could cost approximately $300," Harrell said. "However, Arbor Systems now has equipment that can apply the product more efficiently, so a slightly lower rate may be just as effective using the newer equipment. This could bring the cost down."

Additional lower cost products and methods for controlling pine wilt also are being pursued, Harrell said. This could enable people to treat windbreaks and other pine plantings.

"Since the current cost of the treatment will likely lead to it being used only on high-value trees, people should remove dead trees as quickly as possible and destroy them by either burning, burying or chipping," Harrell said.

Pine wilt has killed an estimated 5,000 pines in Nebraska since entering the state eight years ago. The disease is most common in southeast Nebraska, but also has been found around Fremont, Grand Island, North Platte and Valentine, Harrell said.

The microscopic pinewood nematode disrupts the flow of sap, causing the tree to turn brown and die.