Posted: 04.23.2010

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.

 

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