D. Michael Benson

Professor of Plant Pathology

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

General Interests

Epidemiology and control of ornamental diseases and ecology of root-infecting fungi. Root-infecting fungal pathogens such as Rhizoctonia, Phytophthora, and Pythium spp. are important pathogens in production of ornamental crops as well as in the urban environment. Over the years, 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, 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 biocontrol and suppressive mixes for disease management of root-infecting pathogens as well as other aspects of ornamental disease control.

Research

Ornamentals

Phytophthora dieback of rhododendron

We are developing suppressive potting mixes that utilize biocontrol agents such as binucleate Rhizoctonia fungi, Trichoderma virens, and other potential antagonists of root-infecting fungi as well as animal waste composts. Isolates of Trichoderma (Gliocladium) virens and binucleate Rhizoctonia spp. (BNR) controlled pre-emergence damping-off of Catharanthus roseus (vinca) caused by Pythium ultimum. Pesta formulation of BNR isolates controlled both Rhizoctonia pre- and post-emergence damping-off of impatiens caused by R. solani in plug production studies.

Isolates of Burkholderia (Pseudomonas) cepacia selected for lack of pyrrolnitrin production suggests a critical role for this antibiotic in control of Rhizoctonia stem rot of poinsettia. A crop production system for poinsettia was developed whereby B. cepacia protected poinsettia cuttings from Rhizoctonia stem rot during propagation and BNR fungi in a Pesta formulation protected rooted cuttings following tranplanting to a soilless potting mix. Utilization of animal waste composts as amendments to potting mixes to control root diseases such as Phytophthora and R. solani suggests that loading rates will be limited to less than 20% due to salt injury and unfavorable physical property characteristics at higher rates. Participation in regional research has the potential to expand the use of these biocontrol tactics. Recently, nursery surveys have been conducted for Phytophthora ramorum cause of Sudden Oak Death to confirm that the pathogen has not been introduced to nurseries in North Carolina.

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 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 colleaques in forestry and horticulture. Both Momi and Turkish fir were resistant to the disease. The possibility of grafting Fraser fir onto Momi or Turkish rootstock is under evaluation.

In addition, a long-term breeding project is underway with geneticists in the College of Forestry to develop Fraser fir that is resistant to Phytophthora root rot. Multiple-year plots have been established in field sites where initial Phytophthora foci suggested a disease problem to study the effect of slope, aspect, and environmental parameters on the dispersal of P. cinnamomi within the sites.

Teaching

PP728 Soilborne Plant Pathogens focuses on an-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. View class pathogen profiles on the PP728 homepage.

Extension Activities

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

Recent Publications

• 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.
• Frampton, J. and Benson, D. M. 2004. Phytophthora root rot mortality in Fraser fir seedlings. HortSci. 39:1025-1026.
• 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
• Lamour, K. H., Daughtrey, M. L., Benson, D. M., Hwang, J., and Hausbeck, M. K. 2003. Etiology of Phytophthora drechsleri and P. nicotianae (= P. parasitica) affecting floriculture crops. Plant Dis 87:854-858.
• 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.
• Hwang, J. and Benson, D. M. 2002. Biocontrol of Rhizoctonia stem and root rot of poinsettia with Burkholderia cepacia and binucleate Rhizoctonia. Plant Disease 86:47-53.
• Hwang, J., Chilton, W. S., and Benson, D. M. 2002. Pyrrolnitrin production by Burkholderia cepacia and biocontrol of Rhizoctonia stem rot of poinsettia. Biol. Contr. 25:56-63.
• 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
Box 7629
Raleigh, NC 27695-7629

840 Method Road - Unit 3, Room 205

Tel: (919) 515-3966
Fax: (919) 515-5657
E-mail: mike_benson@ncsu.edu