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Walter F. Mahaffee

walt mahaffee

Associate Professor (Courtesy)

Ph.D., 1996, Auburn University, Alabama


Office/Lab: USDA Horticultural Crops Research Unit
Phone: 541-738-4036/4035

Research Area

Foliar pathology of horticulture crops: development of biological control systems; ecology/epidemiology of pathogens and biocontrol agents; and integrated pest management.

Description of Research

Research focuses on understanding the ecology of microorganisms on plant surfaces, and applying that knowledge to reduce disease development in agronomic settings while enhance the economic and sustainable production of horticultural crops.  Current projects include (1) characterize the biology of foliar and fruit pathogens, particularly powdery mildews and Botrytis cinerea; (2) development of technical infrastructure for regional and national disease forecasting systems for plant diseases; (3) use of inoculum detection as a decision aid for disease management, (4) pathogen dispersion and simulation modeling

Research Group Members

Research Assistants/Associates

Chris Gorman
Tara Neill

Graduate Students

Lindsey Thiessen (PhD due 2016)
Brent  Warneke (MS due 2017)

Related Links

USDA Lab Page


Miller, N.E. Stoll, R., Mahaffee, W.F., Neill, T.M., & Pardyjak, E.R. 2015. An Experimental Study of Momentum and Heavy Particle Transport in a Trellised Agricultural Canopy. Agricultural Forest Meteorology (In Press)

Thiessen, L.D., Keune, J.A. Neill, T.M., Turechek, W.W., Grove, G.G. and Mahaffee, W.M.  2015.  Development of a grower performed inoculum detection assay for management of grape powdery mildew. Plant Pathology (In Press)

Bailey, B. N., Overby, M., Willemsen, P., Pardyjak, E. R., Mahaffee, W. F., & Stoll, R. 2014. A scalable plant-resolving radiative transfer model based on optimized GPU ray tracing. Agricultural Forest Meteorology 198-199;192–208. doi:10.1016/j.agrformet.2014.08.012

Bailey, B. N., Stoll, R., Pardyjak, E. R., & Mahaffee, W. F. 2014. Effect of vegetative canopy architecture on vertical transport of massless particles. Atmospheric Environment 95: 480–489. doi:10.1016/j.atmosenv.2014.06.058.

Mahaffee, W.F. 2014. Use of airborne inoculum detection for disease management decisions. Pp, 39-54.  In: Detection and Diagnostics of Plant Pathogens, M. L. Gullino and P. Bonants, Eds.  Springer Verlag, NY

Gent, D. H., Mahaffee, W. F., Pfender, W. F., McRoberts, N. 2013.  The use and role of predictive systems in disease management.  Annual Review of Phytopathology.  51: 267-289

L. Morin, Gomez, D. R., Evans, K. J.,. Neill, T M., Mahaffee, W. F. and Linde, C. C. 2013.  Invaded range of the blackberry pathogen Phragmidium violaceum in the Pacific Northwest of the USA and the search for its provenance.  Biological Invasions 15:1847-1861

Gent, D. H., Nelson, M. E., Grove, G. G., Mahaffee, W. F., Turechek, W. W., and Woods, J.L. 2012. Association of spring pruning practices with severity of powdery mildew and downy mildew on hop. Plant Disease 96:1343-1351.

Pfender, W. F., D. H. Gent, and W. F. Mahaffee. 2011. Sensitivity of disease management decision aids to temperature input errors associated with out-of-canopy and reduced time-resolution measurements. Plant Disease 95:726-736.

Pfender, W. F., Gent, D. H., Mahaffee, W. F., Coop, L. B. and Fox, A. D. 2011.  Decision aids for multiple-decision disease management as affected by weather input errors. Phytopathology DOI: 10.1094/PHYTO-05-10-0131. 2011

Wallace, P.K., Bruce, A. and Mahaffee, W.F. 02011.  Subsurface examination of a foliar biofilm using scanning electron- and focused-ion-beam microscopy.  Micron   doi:10.1016/j.micron.2011.02.003.  2011.

Johnson, K. B., and Mahaffee, W. F. 2010. Factors influencing epidemiology and management of blackberry rust in cultivated Rubus laciniatus. Plant Dis. 94:581-588.

Anderson C.M., Aparicio G.J., Atangana A.R., Beaulieu J., Bruford M.W., Cain F., Campos T., Cariani A., Carvalho M.A., Chen N., Chen P.P., Clamens A.-L., Clark A.M., D'acier A.C., Connolly P., Cordero-Rivera A., Coughlan J.P., Cross T.S., David B., Bruyn C.D., Meyer M.D., Ridder C.D., Delatte H., Dettori M.T., Downer S.J., Dubreuil C., Evans K.J., Fan B., Ferrara G., Gagné A., Gaillard M., Gigliarelli L., Giovinazzi J., Gomez D.R., Grünwald N.J., Hansson B., Huotari T., Jank L., Jousselin E., Jungmann L., Kaczmarek M.E., Khasa D.P., Kneebone J., Korpelainen H., Kostamo K., Lanfaloni L., Lin H., Liu X., Lucentini L., Maes G.E., Mahaffee W.F., Meng Z., Micali S., Milano I., Mok H.F., Morin L., Neill T.M., Newton C.H., Ostrow D.G., Palomba A., Panara F., Puletti M.E., Quarta R., Quilici S., Ramos A.K.B., Rigaud T., Risterucci A.M., Salomon M.P., Sánchez-Guillén R.A., Sarver S.K., Sequeira A.S., Sforça D.A., Simiand C., Smith B., Sousa A.C.B., Souza A.P., Stepien C.C., Stuckert A.J., Sulikowski J., Tayeh A., Tinti F., Tsang P.C.W., Houdt J.K.J.V., Vendramin E., Verde I., Virgilio M., Wang H.L., Wang L., Wattier R.A., Wellenreuther M., Xie C.X., Zane L., Zhang X.J., Zhang Y., Zhuang Z., Zucchi M.I. (2010) Permanent Genetic Resources added to Molecular Ecology Resources Database 1 December 2009-31 January 2010. Molecular Ecology Resources 10:576-579.

Peetz, A.B., Mahaffee, W.F. , and Gent, D.H. 2009.  Effect of temperature on sporulation and infectivity of Podosphaera macularis on Humulus lupulus.  Plant Disease 93: 281-286

Mahaffee, W.F ., Pethybridge, S., and Gent, D.H. 2008.  Compendium of hop diseases, arthropods, and other disorders.  APS Press, St. Paul, MN. 112 pp.  

Gent, D.H., Turechek, W.W. and Mahaffee, W.F. 2008. Spatial and temporal stability of the estimated parameters of the binary power law.  Phytopathology 98: 1107-1117

Gent, D. H., Barbour, J. D., Grove, G. G., Mahaffee, W. F ., Nelson, M. E., Ocamb, C. M., Peetz, A., and Turechek, W. W.  2007.  A decade of hop powdery mildew in the Pacific Northwest.  Online.  Plant Health Progress doi: 10.1094/PHP-2008-0314-01-RV

Gent, D. H., Turechek, W. W., and Mahaffee, W. F . 2007. Sequential sampling for estimation and classification of the incidence of hop powdery mildew I: Leaf sampling. Plant Dis. 91:1002-1012.

Gent, D. H., Turechek, W. W., and Mahaffee, W. F. 2007. Sequential sampling for estimation and classification of the incidence of hop powdery mildew II: Cone sampling. Plant Dis. 91:1013-1020.

Mahaffee W.F. and Scheuerell, S. J. 2007. Compost teas: Alternatives to traditional biological control agents.  Pp. 165-179. In: Microbial Ecology of Aerial Plant Surfaces. M. Baily, Ed. CABI, Oxford, England.

Gent, D.  Mahaffee, W.F. , and Turechek, W.W.  2006.  Spatial heterogeneity of the incidence of powdery mildew in hop cones.  Plant Disease  90:1201-1208.

Falacy, J.S., Grove, G.G., Mahaffee, W.F. , Larsen, R.C., Glawe, D.A. Vandemark, G.J., and Galloway , H. 2007. Detection of Erysiphe (Uncinula) necator using the Polymerase Chain Reaction and Species-Specific Primers. Phytopathology 97:1290-1297

Scheuerell, S.J. and Mahaffee, W.F. 2006. Variability associated with suppression of gray mold (Botrytis cinerea) on geranium (Pelargonium x hortorum) by non-aerated and aerated compost teas. Plant Disease 90:1201-1208

Scheuerell, S.J. and Mahaffee, W.F. 2005. Inoculation of compost after peak heating needed for the rapid development of damping-off suppression caused by Pythium ultimum. Compost Science 13:65-71.

Scheuerell, S.J. ,Sullivan, D. and Mahaffee, W.F. 2005. Suppression of seedling damping-off caused by Pythium ultimum, Pythium irregulare, and Rhizoctonia solani in compost amended container media . Phytopathology 95:306-315.

Scheuerell, S.J. and Mahaffee, W.F. 2004. Compost tea as a container media drench for suppressing seedling damping-off caused by Pythium ultimum. Phytopathology 94:1156-1163

Turechek, W.W. and Mahaffee, W.F. 2004. Spatial pattern of hop powdery mildew in the pacific northwest. Phytopathology 94:1116-1128.

Henning, J., Townsend, S., Mahaffee, W., Kenny, S. and Honald, A. 2003 Registration of ' Newport ' hop. Crop Science 44:1018-1019

Mahaffee, W.F., Turechek, W.W., and Ocamb, C.M. 2003. Effect of variable temperature on the infection frequency of Podosphaera macularis on Humulus lupulus. Phytopathology 93:1587-1592.

Mahaffee, W., Thomas, C., Turechek, W., Ocamb, C., Nelson, M., Fox, A., and Gubler, W. 2003. Responding to an Introduced Pathogen: Podsphaera macularis (Hop powdery mildew) in the Pacific Northwest . Online Plant Health Progress doi:10.1094/PHP-2003-1113-07-RV.