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Circles of death spread through Wisconsin pines

Blowing in the wind or creeping underground, a circle of death is spreading through Wisconsin”s pine forests.

The description may seem melodramatic, but it paints an accurate picture of what happens when the woods are infested by a fungal pathogen called Heterobasidion, says Glen Stanosz, forest pathologist in the University of Wisconsin-Madison plant pathology department.

The circle of death, a term first coined in Europe, refers to how the disease spreads out to trees farther and farther from the original point of infestation, creating circular pockets of dead trees in the pine stand. In Wisconsin, some of those circles cover a half-acre or more, and they”re still growing, Stanosz says.

The disease has become an epidemic in Wisconsin since it first showed up in a stand of pines in Adams County in 1993. As it spreads, it poses a threat to the industries and recreation that rely on the state”s forests.

“Wisconsin is approximately half covered in forest and the Wisconsin forest industry is a major employer and a major economic factor in the state. We are the number-one producer of pulp for paper products in the entire United States,” Stanosz points out.

The problem is most serious in managed stands or other places where the trees are being cut. The fungus arrives on the breeze, colonizes freshly cut stumps, then migrates down through the root system. Roots in pine forests are intertwined, allowing the fungus to spread from the roots of a colonized tree to those of healthy trees nearby.

“Following the thinning of a pine plantation, or the cutting of a Christmas tree, or the cutting of an ornamental conifer, the fungus travels through the underground roots from tree to tree. What we see in areas affected by this fungus are thinning crowns as the root system slowly deteriorates. Eventually, the needles all turn brown and die,” Stanosz says.

Fungus fruiting structures on the dead and dying trees produce the fungal spores that are carried by the wind and pose a risk to pine trees anywhere in the state. The disease has been confirmed in 21 counties from the southern Wisconsin to Oconto County in the northeast. The challenge, says Stanosz, is to anticipate where it will go.

The good news is that”s there”s a treatment. Infection can be prevented by applying a borax material to the freshly cut stump right after the tree is cut. Loggers who use harvesting machines can fit them with sprayers to treat the stumps as the trees are cut. Others can use backpack sprayers or apply powdered borax. Stanosz recommends landowners specify the treatment in any timber harvesting contract. These treatments are covered by pesticide application regulations.

“If you suspect your woodland is infected, I”d recommend contacting your local DNR office and ask for a visit from the DNR forester or a forest health specialist,” he says.