D. Michael Benson


Dr. D. Michael Benson North Carolina State University Department of Plant Pathology Campus Box 7629 Raleigh, NC 27695-7629 3131 Ligon Street- Unit 3, Room 208 Tel: (919) 515-3966


D. Michael Benson received his B. S. degree in biology from Earlham College and the M.S. and Ph. D. degrees from Colorado State University. After a post-doctoral position at the University of California, Berkeley, he joined the Department of Plant Pathology at North Carolina State University in 1974.  He is currently professor in the department.  He teaches courses on forest pathology, epidemiology and plant disease control, and soilborne plant pathogens.  His research interests include ecology and epidemiology of soilborne plant pathogens with emphasis on biological control and population diversity of root-infecting fungi attacking ornamentals.  Benson has prepared scientific articles, book chapters, and compendium articles with over a 100 peer-reviewed articles. He co-edited with C. Lee Campbell, Epidemiology and Management of Root Diseases (Springer-Verlag, 1994). With Ronald K. Jones he co-edited, Diseases of Woody Ornamentals and Trees in Nurseries (APS Press, 2001) and most recently was co-author with R. G. Linderman of the 2nd edition of theCompendium of Rhododendron and Azalea Diseases and Pests.  As a member of the American Phytopathological Society, he has served on numerous subject matter and policy committees of the Society.  He has been associate editor of Plant Disease, editor-in-chief of Phytopathology, section editor of Canadian Journal of Microbiology, principal editor of Crop Protection, senior editor of APS Press and editor-in-chief of Plant Health Progress. He is a Fellow of APS and an Outstanding Plant Pathologist of the Southern Division of APS.  In addition to APS, Benson is a member of Sigma Xi and a past president of the NC State Chapter of Gamma Sigma Delta.



Epidemiology and control of ornamental diseases and ecology of root-infecting fungi. Root-infecting fungal pathogens such as Phytophthora, Rhizoctonia, and Pythium spp. are important pathogens in production of ornamental crops as well as in the urban environment. Approaches to plant disease management have included modification of cultural practices to suppress pathogens, screening specific ornamental crops such as cultivars and breeding lines of azalea, crabapple, and rhododendron for resistance to pathogens, application and timing of fungicides for disease control, and more recently, genetic diversity of Phytophthora species in ornamental crops and development of biological control agents as an ecological-based approach to integrated pest management (IPM).

Opportunities for graduate students and post-docs with a background in the biological sciences and/or plant pathology exist for studies on characterization of Phytophthora species in ornamental crops as well as biocontrol and suppressive mixes for disease management of root-infecting pathogens.


Phytophthora blight, crown and root rot caused by Phytophthora spp. are serious, crop limiting diseases of floriculture crops produced by greenhouse growers. To understand the diversity of Phytophthora species threatening the floriculture industry, surveys of production facilities in North Carolina were made to collect pathogen isolates.  The majority of isolates were identified as P. cryptogea, P. drechsleri or P. nicotianae, but a few isolates were P. palmivora. All isolates of P. cryptogea were sensitive to mefenoxam, a widely used fungicide for control of Phytophthora diseases, while all isolates of P. drechsleri were insensitive or intermediate in sensitivity to mefenoxam.

Slightly over 20% of the P. nicotianae isolates were insensitive to the fungicide.  Repeated, widespread use of mefenoxam may have resulted in the development of fungicide resistance by these Phytophthora spp.  In order to provide additional management tools, new fungicides have been evaluated as part of the National IR4 Ornamental Program which has the mission to provide safe and effective pest management solutions for growers of specialty crops.  

Christmas trees

In North Carolina, production of Fraser fir (Abies fraseri), the dominant Christmas tree species in the state and expansion of the Christmas tree industry is limited by Phytophthora root rot caused primarily by P. cinnamomi. In a survey of Fraser fir production areas disease incidence was estimated at 9% average loss with quite variable losses in individual fields up to 70%. Alternative fir species were screened for resistance to Phytophthora root rot in a cooperative study with colleagues in forestry. Both Momi and Turkish fir were resistant to the disease.

Use of mulches and amendments to suppress Phytophthora root rot in Fraser fir production takes advantage of naturally-occurring biocontrol microorganisms as well as promotes microbial breakdown of Phytophthora propagules through degradation of cell walls. Combination of mulches and host resistance may allow growers to re-claim lost areas in production fields.

Extension & Outreach: 

Past organizer for the "Ornamental Workshop on Diseases and Insects” held biennially in the mountains of western North Carolina at the Kanuga Conference Center, Hendersonville, NC. Over 130 plant pathologists and entomologists from across the country and Canada usually participate. The 19th Workshop is scheduled for October, 2014.

Selected Publications: 
  • Olson, H. A., and Benson, D. M. 2013. Host specificity and variations in aggressiveness of North Carolina isolates of Phytophthora cryptogea and P. drechsleri in greenhouse ornamental plants. Plant Dis. 97:74-80.
  • Olson, H. A., Jeffers, S. N., Ivors, K. L., Steddom, K. C., Williams-Woodward, J. L., Mmbaga, M. T., Benson, D. M., and Hong, C. X. 2013. Diversity and mefenoxam sensitivity of Phytophthora spp. associated with the ornamental horticulture industry in the southeastern United States. Plant Dis. 97:86-92.
  • Frampton J., Isik, F. and Benson, D. M. 2012. Genetic variation in resistance to Phytophthora cinnamomi in seedlings of two Turkish Abies species. Tree Genetics & Genomes, doi: 10.1007/s11295-012-0529-0
  • Frampton J., and Benson, D. M. 2012. Seedling resistance to Phytophthora cinnamomi in the genus Abies. Annals of Forest Science. doi: 10.1007/s13595-012-0205-4
  • Benson, D. M., and Parker, K. C. 2011. Efficacy of fungicides and biopesticides for management of Phytophthora crown and root rot of Gerber daisy. Online. Plant Health Progress doi:10.1094/PHP-2011-0512-01-RS.
  • Benson, D. M., Parker, K. C., Munster, M., and Ivors, K. L. 2011. First report of stem dieback and leaf spot of Leucothoe caused by Cylindrocladium colhounii in North Carolina. Online. Plant Health Progress doi:10.1094/PHP-2011-0628-01-BR.

  • Kohl, L. M., Warfield, C. Y., and Benson, D. M. 2010. Population dynamics and dispersal of Aphelenchoides fragariae in nursery-grown lantana. J. Nematology 42:332-341.

  • Olson, H.A., and Benson, D.M. 2011. Characterization of Phytophthora species on floriculture crops in North Carolina. Plant Dis. 95:1013-1020.

  • Olson, H. A., Carbone, I., and Benson, D. M. 2011. Phylogenetic history of Phytophthora cryptogea and P. drechsleri isolates from floriculture crops in North Carolina greenhouses. Phytopathology 101:1373-1384.

  • Richter, B. S., Ivors, K. I., Shi, W., and Benson, D. M. 2011. Cellulase activity as a mechanism for suppression of Phytophthora root rot in mulches. Phytopathology 101:223-230.

  • Richter, B. S., D. M. Benson, and K. L. Ivors, 2011. Microbial profiling of cultural systems for suppression of Phytophthora root rot in Fraser fir. Plant Dis. 95:537-546.

  • Olson, H. A., and Benson, D. M. 2010. First report of crown rot caused by Phytophthora tropicalis on gloxinia in North Carolina. Online. Plant Health Progress doi:10.1094/PHP-2010-0708-03-BR.

  • Xu, Z., Gleason, M. L., Mueller, D. S., Esker, P. D., Bradley, C. A., Buck, J. W., Benson, D. M., Dixon, P. M., and Monteiro, J. E. B. A. 2008. Overwintering of Sclerotium rolfsii and S. rolfsii var. delphinii in different latitudes of the United States. Plant Dis. 92:719-724.

  • Ivors, K. L., Abad, Z. G., and Benson, D. M. 2008. Evaluating the pathogenicity of Pythium vexans isolates from Fraser fir in North Carolina. Online. Plant Health Progress doi:10.1094/PHP-2008-1006-01-RS.

  • Olson, H. A. and Benson, D. M. 2007. Induced systemic resistance and the role of binucleate Rhizoctonia and Trichoderma hamatum 382 in biocontrol of Botrytis blight in geranium. Biological Control 42:233–241.

  • Benson, D. M., Grand, L. F., Vernia, C. S., and Gottwald, T. R. 2006. Temporal and spatial epidemiology of Phytophthora root rot in Fraser fir plantations. Plant Dis. 90:1171-1180.

  • Daughtrey, M. and Benson, D. M. 2005. Principles of plant health management for ornamental plants. Annu. Rev. Phytopathol. 43:141-169.

  • Hwang, J. and Benson, D. M. 2005. Identification, mefenoxam sensitivity, and compatibility type of Phytophthora species attaching floriculture crops in North Carolina. Plant Dis. 89:185-190.

  • Benson, D. M., Hall, J. L., Moorman, G. W., Daughtrey, M. L., Chase, A. R., Lamour, K. H.  2002. The history and diseases of poinsettia, the Christmas flower. Plant Health Progress doi:10.1094/PHP-2002-0212-01-RV.

  • Jones, R. K. and Benson, D. M. 2001. Diseases of Woody Ornamentals and Trees in Nurseries, APS Press, St. Paul, MN, 482 pp.