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Philip B. Hamm

Philip Hamm

Extension Plant Pathologist
Hermiston Agricultural Research and Extension Center

Professor, Emeritus
M.S., 1991, Oregon State University, Corvallis


Office/Lab: Hermiston AREC
Phone:541-567-8321Ext. 110










Research Area

Identification and control of diseases impacting vegetable and seed crops; understanding impacts to soilborne pathogens following fumigation; diseases caused by Phytophthora sp.; Identification and control of Potato diseases.

Description of Research

Virus, nematodes and fungal pathogens are responsible for extensive losses in the important vegetable growing region of the Columbia Basin in northeast Oregon and eastern Washington. My research is centered around the identification of the specific pathogens and understanding their lifecycle and then their control through cultural manipulation and/or through chemical and biotechnical methods.

Research Group Members

Graduate Student

Sarah Light

Faculty Research Assistants/Associates

Robert Cating

Biological Aid

Javier Almaguer

The Plant Clinic at Hermiston

Program Manager: Philip Hamm
Laboratory Manager: Robert Cating

The plant clinic in Hermiston provides disease diagnosis and recommendations for disease prevention and control to county extension agents, growers, agricultural consultants, agricultural companies, and home owners in North central & Northeast Oregon and elsewhere. The clinic also provides a fee testing service for many virus diseases and soilborne fungi. Call for details: 541-567-8321

Related Links



Hansen, E. M., P. B. Hamm, A. J. Julis, and L. F. Roth. 1979. Isolation, incidence and management of Phytophthora in forest tree nurseries in the Pacific Northwest. Plant Disease Reporter 63:607-611.

Hansen, E. M., L. F. Roth, P. B. Hamm, and A. J. Julis. 1980. Survival, spread, and pathogenicity of Phytophthora Spp. on Douglas-fir trees planted on forest sites.  Phytopathology 70:422-425.

Hamm, P. B., and E. M. Hansen. 1981. Host specificity of Phytophthora megasperma from Douglas-fir, soybean, and alfalfa. Phytopathology 71:65-68.

Hamm, P. B., and E. M. Hansen. 1982. Single-spore Isolate variation: The effect on varietal designation in Phytophthora megasperma . Canadian Journal of Botany 60:2931-2938.

Hamm, P. B., and E. M. Hansen. 1982.  Pathogenicity of Phytophthora species to Pacific Northwest conifers.  European Journal of Forest Pathology 12:167-174.

Hunger, R. M., P. B. Hamm, C. E. Horner, and E. M. Hansen. 1982.  Tolerance to Metalaxyl by Phytophthora megasperma . Plant Disease 66:645-649.

Hansen, E. M., and P. B. Hamm. 1983. Morphological differentiation of host specialized groups of Phytophthora megasperma . Phytopathology 73:129-134.

Hamm, P. B., and E. M. Hansen. 1983. Phytophthora pseudotsugae , a new species causing root rot on Douglas-fir. Canadian Journal of Botany 61:2626-2631.

Hamm, P. B., and P. A. Koepsell. 1984.  Phytophthora root rot of cabbage and cauliflower in Oregon. Plant Disease 68:533-535.

Hamm, P. B., and E. M. Hansen. 1984.  An improved method for Isolating Phytophthora lateralis  from soil. Plant Disease 68:517-519.

Hamm, P. B., S. J. Cooley, and E. M. Hansen. 1984.  Response to Phytophthora spp. to metalaxyl in forest tree nurseries in the Pacific Northwest. Plant Disease 68:671-673.

Hamm, P. B., E. M. Hansen, and J. R. Sutherland. 1985.  Phytophthora cryptogea and P. drechsleri associated with root-rotted Douglas-fir seedlings in British Columbia.  Plant Disease 69:361.

James, R. L., and P. B. Hamm. 1985. Chlamydospore-producing species of Phoma from conifer seedlings in the Pacific Northwest forest tree nurseries. Montana Academy of Sciences 45:26-36.

Hansen, E. M., C. M. Brasier, D. S. Shaw, and P. B. Hamm. 1986. The taxonomic structure of Phytophthora megasperma : Evidence for emerging biological species groups. Transactions of the British Mycological Society 87:557-573.

Hamm, P. B., and E. M. Hansen. 1987. Identification of Phytophthora spp. associated with conifers in northwest North America. Northwest Science 61:103-109.

Hamm, P. B., A. Kanaskie, P. Morgan, and S. J. Cooley. 1987. Root necrosis caused by Fusarium oxysporum on two-year old Douglas-fir seedlings in Oregon.  Plant Disease 71:651.

Hansen, E. M., and P. B. Hamm. 1988. Canker diseases of Douglas-fir seedlings in Oregon and Washington bareroot nurseries. Canadian Journal of Forest Research 18:1053-1058.

Hansen, E. M., P. B. Hamm, C. G. Shaw III, and P. E. Hennon. 1988. Phytophthora drechsleri in remote areas of southeast Alaska. Transaction of the British Mycological Society 91:379-384.

Hamm, P. B., E. M. Hansen, P. E. Hennon, and C. G. Shaw III. 1988. Pythium Species from forest and muskeg areas of southeast Alaska. Transactions of the British Mycological Society 91:385-388.

Cooley, S. J., and P. B. Hamm. 1988. Susceptibility of northwest conifers to Phytophthora root rot. Tree Planters Notes 40:15-18.

Hansen, E. M., P. B. Hamm, and L. F. Roth. 1989. Testing Port-Orford cedar for resistance to Phytophthora. Plant Disease 73:791-794. 

Hansen, E. M., D. D. Myrold, and P. B. Hamm. 1990. Effects of soil fumigation and cover crops on potential pathogens, microbial activity, nitrogen availability, and seedling quality in conifer nurseries. Phytopathology 80:698-704.

Sansome, E., C. M. Brasier, and P. B. Hamm. 1991.  Phytophthora meadii may be a species hybrid. Mycological Research 95:273-277.

Pscheidt, J. W., J. Z. Burket, S. L. Fischer, and P. B. Hamm. 1992. Sensitivity and clinical use of Phytophthora-specific immunoassay kits. Plant Disease 76:928-932.

Wilcox, F., P. G. Scott, P. B. Hamm, D. N. Kennedy, J. N. Duncan, C. M. Brasier, and E. M. Hansen. 1993. Identity of Phytophthora species attacking raspberry in Europe and North America. Mycological Research 97:817-831.

Brasier, C. M., P. B. Hamm, and E. M. Hansen.  1993. Cultural characters, protein patterns and unusual mating behaviour of Phytophthora gonapodyides isolates from Britain and North America. Mycological Research 97:1287-1298.

Chastagner, G. A., P. B. Hamm, and R. L. Riley. 1995. Symptoms and Phytophthora species associated with a root rot and stem canker disease of Noble fir Christmas trees in the Pacific Northwest. Plant Disease 79:290-293.

Donegan, K. K., D. L. Schaller, J. K. Stone, L. M. Ganio. G. L. Reed, P. B. Hamm, and R. J. Seidler. 1995.  Microbial populations, plant pathogens levels and fungal species diversity, in field plots of potato plants expressing the Bacillus thuringiensis var. tenebrionis endotoxin. Transgenic Plants 5:25-35.

Hamm, P. B., J. R. Jaeger, and L. MacDonald. 1995. Virus diseases of pepper in Northeast Oregon. Plant Disease 79:968.

Clough G. H. and P. B. Hamm. 1995. Coat protein transgenic resistance to watermelon mosaic and zucchini yellows mosaic virus in squash and cantaloupe.  Plant Disease 79:1107-1109.

Inglis, D. A., D. A. Johnson, D. E. Legard, W. E. Fry, and P. B. Hamm. 1996. Relative resistances of potato clones in response to new and old populations of Phytophthora infestans . Plant Disease 80:575-578.

Hansen, E. M. and P. B. Hamm. 1996. Survival of Phytophthora lateralis in infected roots of Port Orford cedar. Plant Disease 80:1075-1078.

Johnson, D. A., T. F. Cummings, P. B. Hamm, R. C. Rowe, J. S. Miller, R. E. Thornton, G. Q. Pelter, and E. J. Sorensen. 1996. Potato late blight in the Columbia Basin: An economic analysis of the 1995 epidemic. Plant Disease 81:107-111.

Hamm, P. B., D. S. Spink, G. H. Clough, and K. S. Mohan. 1997. First report of bacterial fruit blotch of watermelon in Oregon. Plant Disease 81:113.

Miller, J. S., P. B. Hamm, and D. S. Johnson. 1997. Characterization of the Phytophthora infestans population in the Columbia Basin of Oregon and Washington from 1992-1995. Phytopathology 87:656­660.

Johnson, D. A., Alldredge, J. R. and P. B .Hamm.   1998.  Expansion of potato late blight \forecasting models for the Columbia Basin of Washington and Oregon.  Plant Disease 82:642-645.

Miller, J. S., Johnson, D. A., and P. B. Hamm.  1998.  Aggressiveness of isolates of Phytophthora infestans from the Columbia Basin of Washington and Oregon. Phytopathology 88:190-197.

Rykbost, K. A., D.C. Hane, P. B. Hamm, R. Voss, and D. Kirby.  1999. Effects of seedborne potato virus Y on Russet Norkotah performance. American J of Potato Research 76:91-96.

Hane, D.C. and P. B. Hamm.  1999. The effects of seedborne PVY infection in two potato cultivars expressing mild disease symptoms.  Plant Disease 83:43-45.

Hamm, P. B. and G. H. Clough. 1999. Comparison of application methods on deposition and redistribution of chlorothalonil in a potato canopy and potential impact for control of late blight. Plant Disease 83:441-444.

Geary, G., D. A. Johnson, P. B. Hamm, and T. F. Cummings.  1999.  Fungicide application for late blight management: A boom attached to a center pivot irrigation system. Plant Disease 83:512-515.

Hamm, P. B. and D. C. Hane.  1999.  Effects of seedborne Potato Leafroll Virus on Russet Norkotah potato.  Plant Disease 83: 1122-1124.

Brown, C. R., H. Mojtahedi , G. S. Santo, P. B. Hamm, J. J. Pavek, D. Corsini, S. Love, J. Crosslin, and P.E. Thomas. 2000.  Potato Germplasm resistant to Corky Ringspot disease.   American Journal of Potato Res. 77:23-27.

Ingham, R. E., P. B. Hamm, J. P. McMorran, and G. H. Clough.  2000. Occurrence and Management of Paratrichodorus allius. Supplement to the Journal of Nematology 31:678-683.

Johnson, D. A., T. F. Cummings, and P. B. Hamm.  2000. Cost of Management of potato late blight in the Columbia Basin: 1996-1998.  Plant Disease 84:399-402.

Gavino, P. D., C. D. Smart, R. W. Sandrock, J. S. Miller, P. B. Hamm, T. Yun Lee, R. M. Davis, and W. E. Fry. 2000. Implications of sexual reproduction for Phytophthora infestans in the United States: generation of an aggressive lineage.  Plant Disease 84:731-735.

Ingham, R. E., P. B. Hamm, R. E. Williams, and W. H. Swanson.  2000.  Control of Paratrichodorus allius and corky ringspot disease of potato in the Columbia Basin of Oregon. Annals of Applied Nematology 32:566-575.

Ingham, R. E., P. B. Hamm, R. E. Williams, and W. H. Swanson.  2000. Control of Meloidogyne chitwoodi in potato with fumigant and nonfumigant nematicides. Annals of Applied Nematology 32:556-565.

Gallian, J. J., W. M. Wintermantel, and P. B. Hamm.  2001. First report of Rhizomania of sugar beet in the Columbia Basin of Washington and Oregon.  Plant Disease 86:72.

Crosslin, J. M, P. B. Hamm, K. C. Eastwell, R. E. Thornton, C. R. Brown, D. Corsini, P. J. Shiel, and P. H. Berger. 2002.   First report of the necrotic strain of Potato Virus Y (PNY n ) Potyvirus on potatoes in the Northwestern United States. Plant Disease 86:1177.

Johnson, D. A., J. R. Alldredge, and P. B. Hamm.  2003. Aerial photography used for spatial pattern analysis of late blight infected foliage in irrigated potato circles.  Phytopathology 93:805-812.

Hamm, P. B., R. E. Ingham, J. R. Jaeger, K. Volker, and W. H. Swanson. 2003.  Soil fumigant effects on three genera of potential soilborne pathogenic fungi and their effect of potato yield in the Columbia Basin of Oregon.  Plant Disease 87:1449-1456.

Geary, G., P. B. Hamm, and D .A. Johnson. 2004. Application and distribution of fungicides using differing water rates and surfactants for the control of late blight in commercial potato fields. American Journal of Potato Res 81:305-315.

Crosslin, J. M. J. E. Munyaneza, A. Jensen, and P. B. Hamm. 2005. Association of the beet leafhopper (Homoptera: Cicadellidae) with a clover proliferation group phytoplasma in the Columbia Basin of Washington and Oregon.  J. Econ Ent 98:279-283.

Crosslin, J. M., P. B. Hamm, and P. J. Shiel. 2005. Serological and molecular detection of tobacco veinal necrosis isolates of Potato virus Y from the western United States. American Journal of Potato Res. 82:263-270.

Ingham, R.E., P.B. Hamm, E. Riga and K.J. Merrifield. 2005. First report of Pratylenchus penetrans damage to ranger russet potato in the Columbia Basin of Washington. Plant Disease. 89:207

Collins, H.P.,  A. Alva, R. Boydston, R.L. Cochran , P.B. Hamm, A. McGuire, and E. Riga. 2006. Soil microbial, fungal, and nematode responses to soil fumigation and cover crops under potato production. Biol. Fertil. Soils. 42:247-257.

Lorensen, J., P. Shield, P. Berger, J.M. Crosslin, & P.B. Hamm. 2006. Whole genome characterization of Potato Virus Y isolates collected in the western USA and their comparison to isolates from Europe and Canada. Archives of Virology 151: 1055-1074 

Crosslin, J.M., P.B. Hamm, D. Hane, J. Jaeger, C.R. Brown, P.J. Shiel, P. H. Berger, and R.E. Thornton. 2006. The occurrence of PVY o and PVY n strains in potato seed lots planted in Oregon and Washington. Plant Disease 90:1102-1105.

Hamm, P.B., D. A. Johnson and T. Cummings. 2006. The alternate use of air and chemigation application methods for applying fungicides for the control of late blight in potato. Am. J. Potato Res. 83: 473-484.

Geary, B., D. A. Johnson, P. B. Hamm, S. James, and K. A. Rykbost. 2007.  Management of potato silver scurf with the use of chemicals and identification of thiabendazole and thiophanate-methyl resistant isolates of Helminthosporium solani .  Plant Disease 91:315-320.

Ocamb, C. M., P. B. Hamm, and D. A. Johnson. 2007. Fusarium species recovered from potato dry rot in the Columbia Basin of Oregon and Washington: thiabendazole tolerance and ability to decay tubers. Am J. Potato Res.84:169-178

Gieck, S .L., H. R. Pappu, P. B. Hamm and N. L. David. 2007.  First Report of Onion Yellow Dwarf Virus , Leek Yellow Stripe Virus, and Garlic Common Latent Virus in Garlic in Oregon. Plant Disease 91:461.

Ingham R. E., P.B. Hamm, M. Baune, N.L. David and N.M. Wade . 2007. Control of Meloidogyne chitwoodi in Potato with Shank-injected Metam Sodium and other Nematicides.  Journal of Nematology 39:161-168.

Gieck, S. L., N.L. David, P.B. Hamm, J.M. Crosslin and R.E. Ingham. 2007. First report of foliar symptoms in potato due to Tobacco rattle virus in the Pacific Northwest. Plant Health Progress doi:10.1094/PHP-2007-0917-01-BR. 

Hamm, P.B., S.L. Gieck, and N.L. David. 2007. First report of Wheat Soilborne Mosaic (WSBM) on Triticum aestivum in the Columbia Basin of Oregon. Plant Disease 91:1513

Ingham R. E, P.B. Hamm, M. Baune, N.L. David and K.J. Merrifield. 2007.  Control of Paratrichodorus allius and Corky Ringspot Disease in Potato with Shank-injected Metam Sodium. Journal of Nematology 39:258-262

Munyaneza, J.E., A. Jensen, P.B. Hamm, J.E. Upton. 2008 Seasonal Occurrence and Abundance of the Beet Leafhopper (Hemiptera: Cicadellidae) in the Potato Growing Region of Washington and Oregon Columbia Basin. Am J. Potato Res.85:77-84.

Kirk, W.W., S.L. Gieck, J.M. Crosslin and P.B. Hamm. 2008. The First Report of Corky Ringspot caused by Tobacco Rattle Virus on Potatoes (Solanum tuberosum ) in Michiga. Plant Disease 92:485.

Omer, M. A., D.A. Johnson, L.I. Douhan, P.B. Hamm, and R.C. Rowe. 2008. Detection, quantification and vegetative compatibility of Verticillium dahliae in potato and mint production soils in the Columbia Basin of Oregon and Washington. Plant Disease 92:1127-1131.

Hamm, P.B. 2008. Soil-borne Fungi. In: The Cannon of Potato Science: Potato Research 50: 239-241.

Brown, C. R., H. Mojtahedi, J. M. Crosslin, S. James, B. Charlton, R. G. Novy, S. L. Love, M. I. Vales and P. B. Hamm.  2009. Characterization of     Resistance to Corky Ringspot Disease  in Potato: A Case for Resistance to Infection by Tobacco Rattle Virus. American Journal of  Potato Research 86:49-55.

Gieck, S.L., P.B. Hamm, N.L. David, and H.R. Pappu. 2009. First Report of Japanese garlic virus and Garlic virus B in Garlic in the Pacific Northwest. Plant Disease 93: 431.

Porter, L. D., P.B. Hamm, N.L. David, S.L. Gieck, J.S. Miller, D.A. Inglis, and B. Gundersen.2009. Metalaxyl-M-resistant Pythium species in potato production areas of the Pacific Northwest U.S.A. American Journal of Potato Research 86:315-326.  

Hamm, P.B., D. Hane, M.J. Pavek, L.D. Leroux, S.L. Gieck, and N.L. David. 2010. Potato varieties differ in current season infection by potato virus Y (PVY). American Journal of Potato Research 87:19-26.

DeBano, S.J., P.B. Hamm, A. Jensen, S.I. Rondon, and P.J. Landolt. 2010. Spatial and Temporal Dynamics of Potato Tuberworm (Lepidoptera: Gelechiidae) in the Columbia Basin of the Pacific Northwest. Environmental Entomology 39: 1-14

Whitworth, J.L, P.B. Hamm, and C. McIntosh. 2010. Effect of potato virus Y on yield of a clonal selection of Russet Norkotah. American Journal of Potato Research 87:310-314

Crosslin, J.M., P.B. Hamm, W.W. Kirk, and R. W. Hammond. 2010. Complete genomic sequence of a tobacco rattle virus isolate from Michigan-grown potatoes. Archives of Virology 125:621-625

Glawe, D.A., T. Barlow, J. E. Eggers, and P.B. Hamm. 2010. First report of powdery mildew caused by Leveillula taurica of field grown-sweet pepper (Capsicum annuum ) in the Pacific Northwest. Plant Health Progress: July 8, 2010.

Clough, G.H., S.I. Rondon, S.J. DeBano, N. David, and P.B. Hamm. 2009. Reducing tuber damage by the potato tuberworm (leidoptera: Gelechiidae) with cultural practices. Journal of Economic Entomology (In Press)