Annosum root rot

Annosum root rot, caused by the fungus Heterobasidion irregulare, was first found in Wisconsin in 1993. It is considered one of the most destructive diseases of conifers in the northern parts of the world. Prevention of this disease is key, as it is difficult to treat and control. Many tree species can be hosts, but in Wisconsin annosum root rot is most common on red and white pine plantations.

Distribution

Annosum in Wisconsin

Known county distribution of annosum root rot
Confirmed counties in Wisconsin with annosum root rot (as of September 2014)

Since 1993, annosum root rot has been confirmed in 24 Wisconsin counties: Adams, Buffalo, Columbia, Dunn, Grant, Green, Iowa, Jefferson, Juneau, LaCrosse, Marinette, Marquette, Oconto, Portage, Richland, Sauk, Shawano, Taylor, Trempealeau, Walworth, Waukesha, Waupaca, Waushara and Wood.

Annosum root rot is most damaging in plantation-grown conifers (especially pines) where stumps of trees that were cut down offer a place for infection to start and connected roots provide a pathway for annosum to move from tree to tree underground.

Site factors/history

Site factors are characteristics of the specific area where a tree is growing that influence how easy it is for disease to occur there. Site factors include the type of soil, temperature, slope of the land and more that make it easy (or difficult) for disease to occur. The influence of site factors on annosum root rot has recently been studied in Wisconsin and data analysis is in progress.

In the southeastern United States, the disease is more common on former agriculture land with a soil pH of less than 6 than on old forest soils. Sandy or sandy loam soils at least 12 inches (30 cm) deep, with good internal drainage and a low seasonal water table are also considered sites favorable for disease development.

Biology

The cause of annosum root rot

Infection most often happens when basidiospores, produced by the fungus, land and grow on the surface of a freshly cut stump. This infection process is why annosum can be so damaging in an area where trees are cut down.

Infection occurs through freshly cut stump.

Trees that can get annosum root rot

Many tree species can be hosts, but in Wisconsin annosum root rot is most common on red and white pine plantations. On overstory trees, infection has been observed on red, white and jack pines. On understory trees, fruit bodies have been found on red pine, white pine, jack pine, balsam fir, white spruce, eastern red cedar, oaks (both red and white), black cherry and buckthorn.

Of all the species found with the disease, mortality has been observed or suspected on red pine, white pine, jack pine, balsam fir and eastern red cedar. Although the size of a fruit body can be quite large at the base of seedlings, dieback symptoms have not yet been observed on deciduous trees in Wisconsin.

Annosum root rot can spread both above and below ground

Basidiospores are most often produced when the temperature is between 41 and 90 degrees F (5-32 degrees C) and can be carried by the wind over hundreds of miles, though most spores only move to within 300 feet (90 meters).

The fungus starts living in the stump and moves into the root. Where roots connect, it moves from tree to tree at the rate of 3.2- 6.5 feet per year (1-2 m/yr). Although infection through root and lower stem wounds can also occur, the major point of entry for the disease is through freshly cut stumps.

Annosum weakens and breaks down the wood (both lignin and cellulose) and causes a stringy, yellow decay in the roots and lower stem.

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Stringy yellow decay caused by Heterobasidion irregulare.


Impact

The impact of annosum root rot in forests and plantations

Infected white pine seedling
Infected white pine seedling with several Heterobasidion irregulare fruit bodies.

Annosum root rot causes a decay of the roots and lower stem, attacks the cambium and kills infected trees. Infected trees show thin foliage, reduced height, diameter and shoot growth and eventual mortality. Three to eight years after nearby trees are cut down, mortality of individual trees becomes noticeable. Understory seedlings and saplings that are near infected older trees may also become infected. The number of infection centers in a stand can vary widely. As these pockets of trees die, gaps are created in the forest canopy where brush and early successional trees can grow.

Both annosum root rot and red pine pocket mortality can occur in the same stand and even within the same pocket.

Symptoms and Signs

Symptoms of annosum root rot

Infected trees show thin foliage, reduced height, diameter and shoot growth and eventual mortality. Three to eight years after nearby trees are cut down, mortality of individual trees becomes noticeable. "Infection centers" develop as the disease progresses through connected roots underground, including one or many dead trees surrounded by recently dead or dying trees.

Crown die back - one symptom of annosum root rot
Crown die back - one symptom of annosum root rot

Signs of annosum root rot

Infected trees and stumps may have fruit bodies (spore-producing part of the fungus) at the base, often in the area where the roots attach to the tree’s trunk (root collar). These fruit bodies may be located so low on the tree that they are buried under soil and fallen needles. Young fruit bodies look like popcorn. However, under favorable conditions, they grow to be bracket-shaped, reddish brown on the top and white on the underside. Fruit bodies are perennial but deteriorate by some amount each winter.

Popcorn stage
Popcorn stage of Heterobasidion irregulare fruit body.
Fruit body
Heterobasidion irregulare fruit body.
Fruit body underside
Underside of Heterobasidion irregulare fruit body.


Prevention

Once this disease is in a stand, it is very difficult to control. Prevention is the best approach.

Sporax is applied salt-shaker style
Sporax is applied salt-shaker style on the surface of a freshly cut stump.

Preventing annosum root rot with fungicides

  • Sporax (sodium tetraborate decahydrate) is granular and can be applied using a salt-shaker style container or a special dispensing unit made of a PVC pipe and a plastic nozzle.
  • Cellu-Treat (disodium octaborate tetrahydrate) is a water-soluble powder and can be applied using a backpack sprayer or an attachment to a harvester.

Stumps must be treated as soon after cutting as possible (no later than the end of each cutting day). Fungicides will help prevent new infections, but will not stop the growth of the fungus if the stump is already infected. The risk of infection by annosum is higher when a stand is close to infected stands.

It is likely that additional infection centers are present in Wisconsin. Recent research conducted in Wisconsin by the University of Wisconsin-Madison confirmed that there were much higher numbers of viable spores in the air in spring and fall, followed by summer. A risk-based guide is available to help landowners/property managers determine whether the fungicide treatment should be considered to reduce the risk of annosum root rot.

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Application of Sporax to a freshly cut stump using an application device made of a PVC pipe and a plastic nozzle.
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Water-soluble fungicide Cellu-Treat can be mixed with water in a tank and sprayed onto a freshly cut stump using a backpack sprayer.
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An example of mounting a spray device on a processor with a fixed cutting head. A spray nozzle was mounted on the back of the head. Liquid is sprayed from the nozzle right after felling.
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A perforated sawbar, demonstrating liquid fungicide coming out through small holes.

Management

Managing annosum when it is scattered throughout a forest or stand


  1. Expect trees to die in pockets and trees around the pocket edges to have a loss of growth.
  2. During thinnings or salvage operations, it is recommended that dead trees and the bottom eight feet of trees that are showing dieback and/or yellowing of the foliage (fader trees) be left on the site to minimize the movement of fruit bodies to uninfected areas of the state. The top part of fader trees can be used. Minimize felling and skidding wounds.

    Note: Current field studies are investigating the frequency of fruit body formation on dead and fader trees that are infected with annosum root rot in southern Wisconsin. When completed, these studies will provide more data to assess the risk of introduction of the disease in a new area through infected wood with fruit bodies.
     
  3. Cutting and burning dead trees and the bottom eight feet of fader trees on the site will help reduce the formation of fruit bodies.
  4. Trees that seem healthy outside the pocket, extending ½ to 1 chain (1 chain = 66 feet) from the perimeter of the last faders may be harvested to use the wood before they succumb to the disease. It is currently believed that the disease spreads 3.5-6.5 feet per year (1-2 m/year), which gives an estimated expansion of ½ to 1 chain in 10-15 years. This will probably not be effective in preventing or delaying the further spread of the disease through root connection.

    A clear cut of the stand may be considered if the infection is extensive (pockets are connected).
     
  5. To limit the formation of new infection centers during thinning, there are two options:

    1. Treat all freshly cut stumps with fungicides. Fungicides will help prevent new infections but will not stop the movement of annosum through root systems that are already infected.
    2. Provide no treatment to the stumps and expect some additional infection. A native decay fungus, Phlebiopsis gigantea, has been known to invade freshly cut stumps and successfully compete against annosum root rot fungus. The percentage of stumps protected naturally by P. gigantea is unknown.
  6. Start the thinning/harvesting with healthy stands and then move to infected areas. Clean logging equipment (tires, cutting head, etc.) with pressured water before leaving the harvest site to help minimize the risk of spreading annosum root rot to a new location.

    Note: The significance of equipment contamination on the long-distance introduction of this disease is unknown. Annosum spores appear to stay alive in dry soil for one year or longer. Because harvesting equipment creates wounds on stems and roots, and the annosum fungus could enter through a wound and infect a tree, washing at least contacting parts of the equipment before entering uninfected areas is believed to be a good, cautious approach.
     
  7. After harvest, infected sites may be replanted or naturally regenerated to conifers. In the southeastern United States, regeneration losses have been documented to be a total of approximately five percent with additional disease development following thinnings. This data is not yet available for Wisconsin. Some losses of regeneration are expected for our area as mortality of red and white pine regeneration within annosum pockets has been observed. Some deciduous trees are susceptible but tend to sustain lower mortality; a change to hardwoods, if appropriate for the site, should be considered.

    Note: Wisconsin field studies to investigate the survival of regeneration of a variety of native conifer and deciduous tree species are in progress.

Managing annosum when it is rare in a forest or stand


  1. During thinnings or salvage operations, it is recommended that dead trees and the bottom eight feet of trees that are showing dieback and/or yellowing of the foliage (fader trees) be left on the site to minimize the movement of fruit bodies off site to uninfected areas of the state. The top part of fader trees can be used. Minimize felling and skidding wounds.

    Note: Field studies are currently investigating the frequency of fruit body formation on dead trees and fader trees that are infected with annosum root rot in southern Wisconsin. Once completed, these studies will provide us with more data to assess the risk of infected wood on the further spread of the disease.
     
  2. Cutting and burning dead trees and the bottom eight feet of fader trees on the site will help reduce the formation of fruit bodies.
  3. Trees that seem healthy outside the pocket, extending ½ to 1 chain (1 chain = 66 feet) from the perimeter of the last faders may be harvested to utilize the wood before they succumb to the disease. It is currently believed that the disease spreads approximately 3.2-6.5 feet per year (1-2 m/year), which gives an estimated expansion of ½ to 1 chain in 10-15 years. This operation will probably not be effective in preventing or delaying the further spread of the disease through root connection.
  4. To limit the formation of new infection centers during thinning, it is recommended that all freshly cut stumps be treated with fungicides. See the prevention tab to learn more about how to prevent this disease from affecting your trees.
  5. Start the thinning/harvesting with healthy stands and then move to infected areas. Clean logging equipment (tires, cutting head, etc.) with pressured water before leaving the harvest site to help minimize the risk of spreading annosum root rot to a new location.

    Note: The significance of equipment contamination on the long-distance introduction of this disease is unknown. Annosum spores appear to stay alive in dry soil for one year or longer. Because harvesting equipment creates wounds on stems and roots, and the annosum fungus could enter through a wound and infect a tree, washing at least contacting parts of the equipment before entering uninfected areas is believed to be a good, cautious approach.
     
  6. After harvest, the site may be planted or naturally regenerated to conifers. In the southeastern United States, regeneration losses have been documented to be a total of approximately five percent with additional disease development following thinnings. This data is not yet available for Wisconsin. Some losses of regeneration are expected for our area as mortality of red and white pine regeneration within annosum pockets has been observed. Some deciduous trees are susceptible but tend to sustain lower mortality; conversion to hardwoods, if appropriate for the site, should be considered.

    Note: Wisconsin field studies to investigate the survival of regeneration of a variety of native conifer and deciduous tree species are in progress.

Managing for annosum when it is not yet in a forest or stand

If you are planning a thinning, consider treating freshly cut stumps with fungicides. Stumps must be treated as soon as possible after cutting (no later than the end of the day). Fungicides will help prevent new infections but will not stop the growth of the pathogen if the stump is already infected.

The risk of infection by annosum will be higher when a stand is close to infected stands (see the distribution tab to view counties with known cases of annosum root rot). Recent research conducted in Wisconsin by the University of Wisconsin-Madison confirmed that there were much higher numbers of viable spores in the air in spring and fall, followed by summer. A risk based guide is available to help landowners/property managers determine whether the fungicide treatment should be considered to reduce the risk of annosum root rot.

Guide

New annosum root rot guides

A guide for the use of fungicide treatment to prevent annosum root rot in Wisconsin was proposed in 2012. The proposal was the product of the annosum root rot committee and was an effort to balance the future health of the pine resource with our ability to harvest the existing resource efficiently. Public listening sessions were held for public input and written comments for the proposed guide were accepted until July 20, 2012.

Issues and options regarding the proposed plan were presented to the Council on Forestry [exit DNR]. Based on input from the Council and written comments from the public and partners, the treatment guide [PDF] was finalized. The guide is designed to help landowners and property managers determine whether the fungicide treatment should be considered to reduce the risk of annosum root rot on a particular stand (on state-owned lands, state land managers are required to consider the guide at the time of timber sale setup). The guide can also be used by foresters and loggers to help communicate with landowners and property managers about the fungicide treatment option.

The use of the guide is a recommendation for best management practices (BMPs). The guide is recommended for private landowners for consideration (but not required). Private landowners are highly encouraged to learn about the disease and options that will reduce the risk of introducing the disease to their stand. To use the online interactive guide, simply answer a brief series of questions and you can obtain information about whether a fungicide treatment is recommended based on current scientific knowledge and observations in Wisconsin.

For more information, please contact Kyoko Scanlon at Kyoko.Scanlon@Wisconsin.gov or 608-275-3275.

Last revised: Tuesday December 16 2014