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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
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| 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
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| 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
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