Heterobasidion root disease: formerly annosum root disease [Mar. 2013]

Figure 8. Stump treatment spray. Photo by Michelle Cram, USDA Forest Service.
Managing Established Stands

the cut stump using a spray applicator (Figure 8). Watersoluble borate powder, such as Cellu-Treat (disodium octaborate tetrahydrate), has also proven to be successful in thinning operations in pine plantations with a high risk of Heterobasidion root disease. Apply this solution to the stump surface with a spray applicator, to the point of runoff. Sporax, and Cellu-Treat need to be applied within twenty-four hours of harvest.
Summer thinnings below the fall line can reduce the risk from Heterobasidion root disease. Average daily temperatures over ) limit spore production and stump surfaces that reach ) for hours will kill H. irregulare. Summer thinnings may create a bark beetle problem in some areas of the state when beetle populations are high. Be sure to check the status of pine beetle activity in your area before thinning.
Since freshly cut stumps are the primary source of new infections, reducing the number of thinnings in a stand growing on a high-hazard site will reduce the incidence of Heterobasidion root disease.
Pine plantations severely infected with Heterobasidion should be clear-cut and regenerated. Salvage or improvement cuts in severely damaged stands can increase the incidence of Heterobasidion root disease, as well as leave the stand understocked.
Stands with a history of Heterobasidion root disease can be planted with pine immediately after harvesting. Although low percentages of seedlings can become

infected, losses are typically under 10% because diseased roots rot quickly and seedling roots are not yet grafted together. When regenerating high hazard sites, a wider spacing should be used. This will delay the rst thinning and ultimately reduce the total number of thinnings made during the rotation. Low hazard sites require no special planting treatments. Although all southern pines are susceptible to Heterobasidion root disease, longleaf pine is less susceptible and should be considered for planting
on appropriate high-hazard sites.

References

)orest ,nsect 'isease Leaet , 8S 'epartment of Agriculture )orest Service. Annosus 5oot 5ot in (astern Conifers by .athryn 5obbins
)orest Health *uide for *eorgia )oresters, Written by Terry Price, *eorgia )orestry Commission
,nsects and 'iseases of Trees in the South. 1. 8S'A )orest Service - )orest Health Protection
0ichelle Cram, Plant Pathologist, 8S'A )orest Service - )orest Health Protection
www.forestryimages.org

Cover photo - Crown symptoms: Dead and fading trees (left). Photo by Mark Raines, GFC.

Funds for this publication are provided by the USDA Forest Service. Rev. 03/13

Heterobasidion Root Disease
Formerly Annosum Root Disease

Introduction
Means of Spread

Heterobasidion root disease can be a serious problem in pine plantations that have been thinned one or more times. All southern pines are susceptible, but loblolly and slash pine are the most vulnerable. The disease is caused by a tree root rot fungus Heterobasidion irregulare (formerly known as Heterobasidion annosum), which causes decay in the root system. This makes them susceptible to butt rot, windthrow, decreased growth, and ultimately death. )ailure to identify high risk sites and take appropriate measures to reduce potential root disease could prove costly to a landowner.
The fungus usually enters a healthy stand by infecting freshly cut stump surfaces. Airborne basidiospores of the fungus land on a stump's surface, germinate, and produce laments (mycelia), which colonize the stump and its root system. The fungus then spreads to adjacent trees by root grafts or contacts (Figure 1).

Figure 1. Tree-to-tree spread of Heterobasidion by root contact usually results in a more or less circular infection center. After a stand is thinned, the process of infection of stump surfaces, spread through the roots, and death of the remaining, previously healthy trees may occur within 2-3 years. Source: G. Stanosz, U. Wisc. - Madison.

Symptoms

'amage from Heterobasidion root disease may be scattered throughout a stand or occur in pockets of dead and dying pine trees called "infection centers" (Figure 2). Mortality is sometimes preceded by thinning and yellowing of the crown (Figure 3); however, some trees simply turn red and die. Trees in various stages of dying or death may suffer windthrow. ,nfected roots exhibit resin or pitch-soaking (Figure 4) and stringy root decay (Figure 5). Occasionally the fungus will develop fruiting bodies of

conks (Figure 6) at the base of living and dead trees or stumps. These conks are hard to see because they are frequently formed below the litter layer around the tree or stump base, and are most prevalent during the cool wet winter months.
Figure 2. Pockets of dead trees. Photo by Garland N. Mason, USDA Forest Service.
Figure 3. Thinning and yellowing of crowns. Photo by Mark McClure, Georgia Forestry Commission.
Figure 4. Pitch soaked root. Photo by Mark Raines, Georgia Forestry Commission.
Figure 5. Stringy root decay. Photo by Mark Raines, Georgia Forestry Commission.

Figure 6. Conk at base of tree. Photo by Chip Bates, Georgia Forestry Commission.

Hazard Sites

Heterobasidion root disease is found throughout *eorgia on most forested
sites; however, the most perilous areas are
located on deep, sandy ground along the fall line of the state. ,t is best to consult
with a soil scientist or forester for a more
detailed description of a particular site. Figure 7 shows a broad classication of
sites for possible root disease occurrence.

State of Georgia
Low Hazard Moderate Hazard High Hazard Not Rated

Figure 7. Map of Georgia shows soils with high hazard for heterobasidion root disease.

Control

USDA Forest Service Forest Health Protection ODAREHHA#EAH@,Bl?A April 29, 1999
Before thinning, pine stands should be checked to determine the site's susceptibility to Heterobasidion root disease. Soil texture can be evaluated with soil maps or by onsite examination of the soil. The connection between thinning and subsequent infection has focused on treating stumps to prevent or control Heterobasidion root disease. The treatment of freshly-cut stumps with dry granular borax powder, such as Sporax, has proven to be a successful chemical treatment. Sporax may also be mixed with water and applied to