Associate Professor

Department of Plant Pathology
239 Partners III, Campus Box 7567
Raleigh, NC 27695-7567

Telephone: (919) 513-2188 (Office),
Fax: (919) 513-0024,
Lab: (919) 515-0028,
Email :


Ph.D. (Plant Pathology), University of Georgia, Athens, GA, 2004
M.Sc. (Plant Pathology), University of Nairobi, Kenya, 1997
B.Sc. (Agriculture), First Class Honors, University of Nairobi, Kenya, 1994


Program Overview:
My research interest encompasses botanical epidemiology and integrated management of plant diseases, with emphasis on understanding the basic biology and ecology of plant pathogens and the use of this information to develop disease management tools. Application of mathematical and statistical models and computer technology to describe the dynamics of plant diseases in space and time is an integral aspect of my research program whose primary goal is to develop management decisions based on risk assessment and prediction of outbreaks of epidemics. I am also exploring research that bridges botanical epidemiology and pathogen population genetics.

Effective disease management through disease prediction and risk assessment requires an understanding of the biology and ecology of plant pathogens. Basic research is routinely conducted to understand the effects of changing weather patterns, shifts in pathogen populations, host resistance, and changes in cropping practices on the appearance of new and resurgence of existing plant diseases. My lab employs mathematical, statistical and computer models to study these effects and their possible consequences on disease development in space and time. I take advantage of modern statistical and ecological techniques, advanced computer technology and large weather databases to develop and use prediction and risk assessment models as decision-making tools in the integrated management of plant diseases.

Ongoing research projects:

  1. Incorporating random effects in survival analysis of plant disease epidemics and developing sampling techniques for assessment of disease incidence
  2. Developing a risk assessment model for Stagonospora nodorum blotch in winter wheat
  3. Within-season risk assessment model for cucurbit downy mildew and validation of the downy mildew forecasting system (
  4. Population biology and ecology of downy mildew of cucurbits in the eastern United States.
  5. Impact of the soil population structure of members of Aspergillus section Favi on the efficacy of bio-control of aflatoxin in corn.

Current Graduate Students:

  1. Mary Lewis (MS) — Started Fall 2012. Project: Impact of the soil population structure of members of Aspergillus section Favi on the efficacy of bio-control of aflatoxin in corn.
  2. Katie Neufeld (PhD) — Started Fall 2012. Project: Development of a model for within-season fungicide application to control cucurbit downy mildew.
  3. Anna Thomas (PhD) — Started Fall 2011. Project: Population biology and ecology of P. cubensis(cucurbit downy mildew) in the eastern US.
  4. Lucky Mehra (PhD) — Started Spring 2011. Project: Predicting the infection risk of Stagonospora nodorum blotch in winter wheat.


  1. PP 790: Epidemiology: Theory & Application (Fall semester).
  2. PP 790-004: Advances in Evolutionary Ecology & Population Biology (Alternate Spring semester).

Selected Publications
P.S. Ojiambo, D.H. Gent, L.M. Quesada-Ocampo, M.K. Hausbeck and G.J. Holmes. 2015. Epidemiology and population biology of Pseudoperonosporacubensis: A model system for management of downy mildews. Annual Review of Phytopathology 53: (in review).

G.J. Holmes, P.S. Ojiambo, M.K. Hausbeck, L.M. Quesada-Ocampo and A.P. Keinath. 2015. Resurgence of cucurbit downy mildew in the United States: A watershed event for research and extension. Plant Disease 99: (in press).

Rahman, P.S. Ojiambo and F. Louws. 2015. Initial inoculum and spatial dispersal of Colletotrichum gloeosporiodies, the causal agent of strawberry anthracnose crown rot. Plant Disease 99:80-86.

Twiyezimana, P.S. Ojiambo, R. Bandyopadhyay and G.L. Hartman. 2014. Use of quantitative traits to assess aggressiveness of Phakospora pachyrhizi isolates from Nigeria and the United States. Plant Disease 98: 1261-1266.

J. Atehnkeng, P.S. Ojiambo, P.J. Cotty and R. Bandyopadhyay. 2014. Field efficacy of mixtures of atoxigenic Aspergillus flavus vegetative compatibility groups in mitigating aflatoxin contamination in maize. Biological Control 72:62-70.

P.S. Ojiambo and E.L. Kang. 2013. Modeling spatial frailties in survival analysis of cucurbit downy mildew epidemics. Phytopathology 103: 216-227.

K.N. Neufeld, S.A. Isard, and P.S. Ojiambo. 2013. Relationship between disease severity and escape of P. cubensis sporangia from a cucumber canopy during downy mildew epidemics. Plant Pathology 62: 1366-1377.

Zandjanakou-Tachin, P.S. Ojiambo, I. Vroh-Bi, A. Tenkouano, Y.M. Gumedzoe and R. Bandyopadhyay. 2013. Pathogenic variation of Mycosphaerella species infecting banana and plantain in Nigeria. Plant Pathology 62: 298-308.

A.D. Call, T.C. Wehner, Holmes, G.J., and P.S. Ojiambo. 2013. Effect of host plant resistance and fungicides on severity of cucumber downy mildew. HortScience 48: 53-59.

A.D. Zearfoss, T.L. Friesen, Z. H. Liu, P. S. Ojiambo and C. Cowger. 2012. Novel necrotrophic effectors from Stagonospora nodorum and corresponding host genes in winter wheat germplasm in the Southeastern United States. Phytopathology 102: 498-505.

K.N. Neufeld and P.S. Ojiambo. 2012. Interactive effects of temperature and leaf wetness duration on sporangia germination and infection of cucurbit host types by Pseudoperonospora cubensis. Plant Disease 96:345-353.

A.D. Zearfoss, C. Cowger and P.S. Ojiambo. 2011. A degree-day model for the latent period of Stagonospora nodorum blotch in winter wheat. Plant Disease 95:561-567.

P.S. Ojiambo, and G.J. Holmes. 2011. Spatiotemporal spread of cucurbit downy mildew in the eastern United States. Phytopathology 101:451-461.

Twizeyimana, P.S. Ojiambo, J.S. Haudenshield, G. Caetano-Anollés, K.F. Pedley, R. Bandyopadhyay and G.L. Hartman. 2011. Genetic structure and diversity of the Phakopsora pachyrhizi isolates from soyabean. Plant Pathology 60:719-729.

P.M. Diedhiou, R. Bandyopadhyay, J. Atehnkeng and P.S. Ojiambo. 2011. Aspergillus colonization and aflatoxin contamination of maize and sesame kernels in two agro-ecological zones in Senegal. Journal of Phytopathology 159:268-275.

R.O. Nyankanga, O.M. Olanya, P.S. Ojiambo, H.C. Wien, C.W. Honeycutt and W.W. Kirk. 2011. Validation of tuber blight (Phytophthora infestans) prediction model. Crop Protection 30:547-553.

Twizeyimana, P.S. Ojiambo, G.L. Hartman, and R. Bandyopadhyay. 2011. Dynamics of soybean rust epidemics from sequential plantings of soybean cultivars in Nigeria. PlantDisease 95:43-50.

P.S. Ojiambo, G.J. Holmes, W. Britton, W., T. Keever, M.L., Adams, M. Babadoost, S.C. Bost, R. Boyles, M. Brooks, J. Damicone, M.A. Draper, D.S. Egel, K.L. Everts, D.M. Ferrin, A.J. Gevens, B.K. Gugino, M.K. Hausbeck, D.M. Ingram, T. Isakeit, A.P. Keinath, S.T. Koike, D. Langston, M.T. McGrath, S.A. Miller, R. Mulrooney, S. Rideout, E. Roddy, K.W. Seebold, E.J. Sikora, A. Thornton, R.L. Wick, C.A. Wyenandt, and S. Zhang. 2011. Cucurbit downy mildew ipmPIPE: a next generation web-based interactive tool for disease management and extension outreach. Online. Plant Health Progress doi:10.1094/PHP-2011-0411-01-RV.

P.S. Ojiambo, P.A. Paul, and G.J. Holmes. 2010. A quantitative review of fungicide efficacy for managing downy mildew in cucurbits. Phytopathology 100:1066-1076.

L.F. Arauz, K.N. Neufeld, A.L. Lloyd and P.S. Ojiambo. 2010. Quantitative models for germination and infection of Pseudoperonospora cubensis in response to temperature and duration of leaf wetness. Phytopathology 100:959-967.

P.S. Ojiambo and H. Scherm. 2010. Efficiency of adaptive cluster sampling in estimating plant disease incidence. Phytopathology 100:663-670.

Kanetis, G.J. Holmes and P.S. Ojiambo. 2010. Survival of Pseudoperonosporacubensis sporangia exposed to solar radiation. Plant Pathology 59:313-323.

Kanetis, X. Wang, P.A. Wadl, K. Neufeld, G.J. Holmes, P.S. Ojiambo, M. Cubeta and R. Trigiano. 2009. Development of simple sequence repeat markers for the cucurbit downy mildew pathogen, Pseudoperonospora cubensis. Molecular Ecology Resources 9:1460-1559.

O.M. Olanya, P.S. Ojiambo, R.O. Nyankanga, C.W. Honeycutt and W.W. Kirk. 2009. Recent developments in managing tuber blight of potato (Solanum tuberosum) caused by Phytophthora infestans. Canadian Journal of Plant Pathology 31: 280-289.

Twizeyimana, P.S. Ojiambo, K. Sonder, T. Ikotun, G.L. Hartman and R. Bandyopadhyay. 2009. Pathogenic variation of Phakopsora pachyrhizi infecting soybean in Nigeria. Phytopathology 99:353-361.

Zandjanakou-Tachin, I. Vroh-Bi, P.S. Ojiambo, A. Tenkouano, M. Gumedzoe and R. Bandyopadhyay. 2009. Identification and genetic diversity of Mycosphaerella species on banana and plantain in Nigeria. Plant Pathology 58:536-546.