Diagnosing and Managing for Root Disease in Southern Pines

Researchers issue Forest Health Newsletter

Heterobasidion irregulare conk at the base of a pine tree. Photo by Michelle Cram, U.S. Forest Service.
Heterobasidion irregulare conk at the base of a pine tree. Photo by Michelle Cram, USFS.

Southern Regional Extension Forestry (SREF) recently published a new technology bulletin on the biology, diagnosis, and management of Heterobasidion root disease in southern pines. U.S. Forest Service plant pathologists Tyler Dreaden, Southern Research Station (SRS), and Michelle Cram, Forest Health Protection, co-authored the publication with Jason Smith from the University of Florida and SREF’s David Coyle.

Heterobasidion root disease (HRD) — previously called annosum, annosus, or Fomes root disease or root rot — is one of the most economically damaging forest diseases in the Northern Hemisphere. In the southeastern U.S., the disease is caused by the pathogen Heterobasidion irregulare, which infects loblolly, longleaf, pitch, shortleaf, slash, Virginia, and white pine as well as eastern red cedar and incense cedar. The fungus causes root decay, which increases the risk of windthrow and tree mortality.

The publication includes a detailed description and illustrations of the process and symptoms of infection, noting that since HRD symptoms overlap with other diseases, definitive field diagnosis requires identifying H. irregulare fruiting bodies (conks) or lab confirmation of the pathogen. Conks can be found in the duff layer at the base of infected trees and stumps when moisture is high and average daily temperatures are below 70°F.

White stringy rot from H. irregulare decaying a pine root. Photo by Michelle Cram, U.S. Forest Service.
White stringy rot from H. irregulare decaying a pine root. Photo by Michelle Cram, U.S. Forest Service.

In the southeastern U.S., soil characteristics are used to rate the hazard of HRD for a site. High hazard sites have sandy or sandy loam soils at least 12 inches deep with good internal drainage and low seasonal water tables. Losses are generally greater on former agricultural lands than in forests.

The bulletin includes detailed instructions for managing both infected and uninfected stands on high-hazard sites. The following treatments are commonly used to reduce tree losses from HRD on high hazard sites:

  • To reduce primary stump infections on high hazard sites, apply stump treatments when thinning in white pines and southern pines.
  • Thin in summer in stands on high hazard sites south of 34°N latitude.
  • Leave wider spacing between trees to delay and reduce the required number of thinnings.
  • Select species that are less susceptible to the pathogen – such as longleaf pine – to plant on high hazard soils.

For the full details, download the pdf of the publication.

For more information, email Tyler Dreaden at tdreaden@fs.fed.us

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