Stephen Fraedrich

Plant Pathologist
Insects, Diseases, and Invasive Plants (RWU 4552)
USDA Forest Service


  • Clemson University, Ph.D. Forestry/Forest Pathology, 1987
  • Clemson University, M.S. Plant Pathology, 1980
  • Old Dominion University, B.S. Biology, 1978

Professional Experience

  • Research Plant Pathologist, USDA Forest Service (SEFES), Olustee, FL (1987-1994)
  • Research Plant Pathologist, USDA Forest Service (SRS), Athens, GA (1994- present)

Research Interests

My research is broadly focused on the etiology, epidemiology, and management of diseases in southern forest ecosystems caused by native and non-native fungal pathogens, insect-disease complexes, and management of diseases affecting production of seeds and seedlings in seed orchards and nurseries, respectively.

Current Research

Laurel Wilt and Associated Projects

Etiology and Epidemiology of Laurel Wilt on Redbay, Sassafras and Other Lauraceous Species in the Southeastern US

Our initial studies focused on understanding disease development in redbay and sassafras and the potential for other plant species in the United States to be affected by the disease (Fraedrich et al., 2008; Fraedrich, 2008; Smith et al, 2009). Subsequent studies have examined the influence of laurel wilt and other pest problems on pondberry and pondspice (Fraedrich et al. 2012), and most recently we have examined the association of R. lauricola and X. glabratus with dieback in camphortree, a species indigenous to Southeast Asia (Fraedrich et al. 2015). The spread of the disease on sassafras to west-central Alabama (Bates et al. 2013) and the very recent “jump” in the disease to northern Louisiana present particular concerns about how the disease is being spread.

Collaborators: Iowa State University, USFS Forest Health Protection R8, Georgia Forestry Commission, Florida Division of Forestry, South Carolina Forestry Commission, University of Florida, other Forest Service scientists in SRS 4552 and elsewhere.

Association of Raffaelea lauricola and Other Raffaelea spp. with the Redbay Ambrosia Beetle

Studies have examined the fungal associates of X. glabratus and we have documented at least six Raffaelea spp., including R. lauricola, associated with the beetle in the southeastern USA (Harrington et al, 2010; Harrington and Fraedrich, 2010). A subsequent examination of X. glabratus beetles from Taiwan and Japan found that R. lauricola was a consistent associate indicating that the pathogen was introduced with the beetle from Asia (Harrington et al, 2011). The possible roles of the various Raffaelea spp. in the biology of X. glabratus and their ability to cause disease in plants are presently not understood.

Collaborators: Iowa State University, USFS Forest Health Protection R8, Georgia Forestry Commission, Taiwanese Institute of Forest Research, Japanese Forest Research Institute, other SRS 4552 scientists.

Association and Identification of Symbiotic Fungi Associated with Ambrosia Beetles

The association of a highly pathogenic fungal symbiont with X. glabratus has called attention to developing a better understanding of the fungi associated with ambrosia beetles, particularly those associated with introduced beetles. Efforts are currently underway to characterize and identify fungal associates with beetles, and develop more rapid techniques for their characterization and identification. Recent work has described the mycangial associate of Xylosandrus crassiusculus and has identified it as Ambrosiella roeperi, a previously undescribed fungus (Harrington, et al., 2014).

Collaborators: Iowa State University, University of Missouri, USFS Forest Health Protection R8, other SRS 4552 scientists.

Thousand Cankers Disease (TCD)

Development of Phytosanitary Log Treatments and Characterization of Fungi Associated with TCD in the Southeastern US

Branch and stem attacks on walnut trees by Pityophthorus juglandis and subsequent development of lethal cankers by Geosmithia morbida are the reported to be the cause of TCD in the western US. The beetle and fungus are native to the southwestern US and Mexico, and have been introduced into localized areas in the eastern United States. A steam heat treatment schedule was developed that kills the TCD causal organisms in walnut logs (Mayfield et al. 2014). I am currently involved in evaluating a fumigation schedule for the eradication of the beetle and fungus from infested logs. In addition, G. morbida has been inconsistently isolated from beetle-damaged logs in our studies although other potential plant pathogens have been isolated. Further work is needed to identify and examine pathogenicity of other fungi associated with this problem in the East.

Collaborators: University of Tennessee, USFS Forest Health Protection R8, USDA-APHIS-CPHST, other SRS 4552 scientists.

Nurseries – Pest Management and Seedling Quality

Biology and Management of Plant Parasitic Nematodes Affecting Seedling Production

Nematodes are among the most damaging agents of seedlings in southern forest tree nurseries. Our research on cover crops used in southern forest nurseries has found that sorghum and rye are excellent hosts for Tylenchorhynchus ewingi and T. claytoni; however, certain varieties of pearl millet have been found to be nonhosts for these nematodes (Cram and Fraedrich, 2010; Fraedrich et al. 2012). Future testing will include evaluations of additional varieties of pearl millet as well as other species that could potentially be used as cover crops.

Collaborators: USFS Forest Health Protection R8; Arborgen, other state and cooperate nurseries.

Effect of Arbuscular Mycorrhizae (AM) on Seedling Quality

Stunting of eastern red cedar seedlings is a problem in some southern forest tree nurseries. Applications of arbuscular mycorrhizae to soil and planting media have been beneficial for resolving similar seedling production problems in western nurseries. Field and growth chamber studies are being conducted to evaluate the potential benefits of several formulations of arbuscular mycorrhizal products currently available to nursery managers.

Collaborators: Forest Health Protection, R8; Virginia Department of Forestry.

Other Disease and Possible Disease-Related Issues Which Have Come to My Attention

Sirococcus shoot blight of hemlock (Stanosz, et al., 2010), hemlock dieback unrelated to HWA, sugarberry/hackberry decline, problems with redbud, oak dieback/decline, sweetgum dieback, and numerous other problems.

Collaborators: University of Wisconsin, University of Georgia, Georgia Forestry Commission, South Carolina Forestry Commission, Alabama Forestry Commission, Forest Health Protection R8; other SRS scientists as well as others.