D. Michael Benson

Professor of Plant Pathology

• B.S. (Biology), Earlham College
• M.S., Ph.D. (Plant Pathology), Colorado State University

Research

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.

Ornamentals

Phytophthora root rot of gerber daisy

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. drechlseri or P. nicotianae, but a few isolates were P. palmivora.   All isolates of P. cryptogea were insensitive or intermediate in sensitivity to mefenoxam, a widely used fungicide for control of Phytophthora diseases.  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

Phytophthora root rot of Fraser fir

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.

Teaching

PP318 Forest Pathology provides students with general knowledge of plant pathology as it pertains to forest and urban trees. The major types of tree diseases and deterioration of wood and wood products are studied, with emphasis on principles of plant pathology, economic impacts, disease diagnosis, disease-causing agents, mechanisms of pathogenesis, and disease management. Co-instructor with Dr. L. F. Grand. The course website is open during spring semester. A distance education version of the course is planned beginning fall semester 2009.

PP506 Epidemiology and Plant Disease Control considers fundamental concepts and principles of epidemiology as applied to modern strategies of plant disease control. Special consideration given to evaluation of current techniques for control of fungal, bacterial, viral and nematode pathogens in an integrated crop protection system. Co-instructors Dr. Barbara Shew, and Dr. Turner Sutton. The course website is open during spring semester.

PP728 Soilborne Plant Pathogens is an in-depth study of the ecology of soilborne fungal pathogens inducing root and wilt diseases in plants. Concepts and principles including but not limited to the rhizosphere, inoculum potential, soil fungistasis, survival, root disease models and biological control. Students prepare pathogen profiles and format as web pages . The course website is open during fall semester in even years.

Extension Activities

Participation in field days and education workshops to describe plant diseases affecting ornamentals in North Carolina and their control. Several 'Ornamentals Disease Information Notes' and recommendations for ornamental disease control in the North Carolina Agricultural Chemicals Manual are available.

Outreach

Co-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. In 2008, over 135 plant pathologists and entomologists from 27 states plus Canada participated. The 17th Workshop is scheduled for September 20-24, 2010.

Selected Publications

• 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.

• Fichtner, E. J., Benson, D. M., Diab, H. G. and Shew, H. D. 2004. Abiotic and biological suppression of Phytophthora parasitica in a horticultural medium containing composted swine waste. Phytopathology 90:780-788

• Diab, H., Hu, S., and Benson, D. M. 2003. Suppression of Rhizoctonia solani on impatiens by enhanced microbial activity in composted swine waste amended potting mixes. Phytopathology 93:1115-1123.

• Hwang, J., and Benson, D. M. 2003. Expression of induced systemic resistance in poinsettia cuttings against Rhizoctonia stem rot by treatment of stock plants with binucleate Rhizoctonia. Biol. Control 27:73-80.

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

Contact Information

Dr. D. Michael Benson
North Carolina State University
Department of Plant Pathology
Campus Box 7629
Raleigh, NC 27695-7629

840 Method Road - Unit 3, Room 208

Tel: (919) 515-3966
E-mail: mike_benson@ncsu.edu