Christmas tree farm.

2014-15 Rapid Ag: Combat Heterobasidion Root Rot in Minnesota

November 30, 2014

Principal Leader

Robert A. Blanchette


Plant Pathology

Funding Awarded

  • 2014 Fiscal Year: $77,711 
  • 2015 Fiscal Year: TBD

The Problem

Minnesota conifer forests, ornamental plantings and Christmas tree plantations are under threat from a new serious root rot disease. This devastating disease causes over a billion dollars in losses annually in other parts of the United States but has not yet been found in Minnesota. The introduction of the disease into Wisconsin, its rapid spread and current location just a few miles from the Minnesota border prompts the need for immediate action.


Heterobasidion root rot is considered the most economically important disease of pines and other conifers throughout the Northern temperate regions. In the United States it causes over 1 billion dollars in losses annually. It also has tremendous ecological impacts on forest health and productivity. Heterobasidion root rot is well established and causes extensive losses in the eastern and western United States. This disease has not been found in Minnesota. However, there is one report of this fungus from Itasca State Park but this record is suspect and the information has not been confirmed or published. 

Although Minnesota has been free of this horrific tree disease, this likely will not be the case for very long. Recently, it has become well established in Wisconsin and has spread quickly. The Wisconsin Department of Natural Resources reports in 2012 that it has been confirmed in 23 counties and three of these counties are adjacent to Minnesota. This disease, attacking the roots of trees and causing tree mortality, is caused by a complex of Heterobasidion species. It has a wide host range (over 200 species of woody plants) and attacks all conifers and some hardwoods. It is the major disease of pines throughout the northern hemisphere and both red pine and white pine are very susceptible to this pathogen. Once a tree is infected it moves out to adjacent trees by root to root contact causing mortality centers or circles of tree death.

The fungus produces several types of spores (basidiospores in shelflike fruiting bodies and asexual spores over the surface of infected wood) that facilitate fast dispersal. The disease situation in Wisconsin escalated quickly because there was no rapid method to detect the disease and control was delayed. It takes several years for signs of the fungus to be evident on dead and dying trees and once it had been detected, the disease was already well established in the state. To successfully manage this disease in Minnesota and reduce its economic and ecological impact, early detection is essential. This will allow management practices to be deployed to control the disease. 

With so many infection centers in Wisconsin, many of them just a few miles from the Minnesota border, many people believe the disease is already present in Minnesota. If it is not here it will be very soon and the time to act is now. Molecular methods for detecting Heterobasidion have been reported but a rapid, effective method of detection is desperately needed to identify this fungus from infected wood. Our aim is to develop a molecular based diagnostic method using specifically designed primers derived from sequences of Wisconsin isolates of Heterobasidion that is easy to use and effective. We will work cooperatively with the Wisconsin DNR, Minnesota DNR, Minnesota Department of Agriculture and the U.S. Forest Service to use this method in surveys throughout the state. Management plans that include silvicultural, chemical and biological control will also be developed. In addition, an informative web site about this disease will be established as well as an outreach campaign to inform foresters, arborists, the forest based industries and the public about this disease and our efforts to control it. This is one disease where we can limit its impact if we act now before it has become widely established. There is no question that this disease, once it has become established, will cause the loss of millions of forest and ornamental conifer trees in Minnesota.


  1. Detection and development of new diagnostic tools
  2. Management
  3. Outreach
Heterobasidion with tell-tale fruiting bodies.

A conifer tree with the tell-tale fruiting bodies of Heterobasidion disease.  U of M researchers are focused on finding earlier ways to detect the disease to help reduce its potential impact.