College of Agricultural, Human, and Natural Resource Sciences

Department of Plant Pathology

Dennis A. Johnson

Plant Pathologist, Extension Plant Pathologist, and Professor

Potato, Mint and Asparagus Diseases

Research Specialty and Interests

Epidemiology and management of diseases of irrigated crops, and ecology of plant pathogens on natural vegetation. Areas of published research articles include disease resistance, disease forecasting, spatial patterns of diseased plants, disease etiology, and disease management. Host plants of which research articles have been published include the following: potato, mint, asparagus, hop, sweet cherry, onion, barley, wheat, corn, oat, and water lilies.

Professional Experience

  • WSU Assistant, Associate, and Professor and Plant Pathologist 1980-present.
  • Texas A&M University, Texas Agri. Exp. Sta., Assistant Plant Pathologist 1978 and 1979.
  • Plant disease and agricultural advisor in Java, Indonesia January, 1989.

Awards and Professional Activities

  • Friend of the Mint Industry – 1994
  • Canadian Phytopathological Society
  • Honorary Life Member of Potato Association of America- Elected 2009
  • President of American Phytopathological Society – Pacific Division; 2008-2009
  • Fellow of American Phytopathological Society – Elected 2011

Selected Publications

  • Johnson, D.A., Dung, J.K.S., Cummings, T.F., and Schroeder, B.K. 2011. Development and suppression of aerial stem rot in commercial potato fields. Plant Dis. 95:285-291.
  • Johnson, D.A., 2010. Transmission of Phytophthora infestans from infected potato seed tubers to emerged shoots. Plant Dis. 94:18-23.
  • Johnson, D.A., and Dung, J.K.S. 2010. Verticillium wilt of potato – the pathogen, disease and management. Can. J. of Plant Pathol. 32:58-67.
  • Johnson, D.A., and Cummings, T.F. 2009. Latent infection of potato seed tubers byPhytophthora infestans during long term cold storage. Plant Dis. 93:940-946.
  • Johnson, D.A., Cummings, T.F., Abi Ghanem, R., and Alldredge, J.R. 2009. Association of solar irradiance and days of precipitation with incidence of potato late blight in the semiarid environment of the Columbia Basin. Plant Dis.93:272-280.
  • Johnson, D.A., and Atallah, Z.K. 2006. Timing fungicide applications for managing Sclerotinia stem rot of potato. Plant Dis. 90:755-758.
  • Johnson, D.A., Zhang, H., and Alldredge, J.R. 2006. Spatial pattern of Verticillium wilt in commercial mint fields. Plant Dis. 90:789–797.
  • Johnson, D.A., Inglis, D.A., and Miller, J.S. 2004. Control of potato tuber rots caused by oomycetes with foliar applications of phosphorous acid. Plant Dis. 88:1153-1159.
  • Johnson, D. A., Alldredge, J. R., Hamm, P. B., and Frazier, B.E. 2003. Aerial photography used for spatial pattern analysis of late blight infection in irrigated potato circles. Phytopathology 93:805-812.
  • Johnson, D. A., Inglis, D. A., and Miller, J. S. 2004. Control of potato tuber rots caused by oomycetes with foliar applications of phosphorous acid. Plant Dis. 88:1153-1159.
  • Porter, L. D., and Johnson, D. A. 2004. Survival of Phytophthora infestans in surface water. Phytopathology 94:380-387.
  • Porter, L. D., Inglis, D. A., and Johnson, D. A. 2004. identification and characterization of resistance to Phytophthora infestans in leaves, stems, flowers, and tubers of potato clones in the pacific Northwest. Plant Dis. 88:965-972.
  • Porter, L. D., Dasgupta, N., and Johnson, D.A. 2005. Effects of tuber depth and soil moisture on infection of potato tubers in soil by Phytophthora infestans. Plant Dis. 89:146-152.
  • Atallah, Z. K., Larget, B., Chen, X., and Johnson, D. A. 2004. High genetic diversity, phenotypic uniformity, and evidence of outcrossing in Sclerotinia sclerotiorum in the Columbia Basin of Washington State. Phytopathology 94:737-742.
  • Atallah, Z. K., and Johnson, D. A. 2004. Development of Sclerotinia stem rot in potato fields in south-central Washington. Plant Dis. 88:419-423.
  • Johnson, D. A., Alldredge, J. R., and Vakoch, D. L. 1996. Potato late blight forecasting models for the semiarid environment of southcentral Washington. Phytopathology 86:480-484.
  • Johnson, D. A. 1995. Races of Puccinia menthae in the Pacific Northwest and interaction of latent period of mints infected with rust races. Plant Dis. 79:20-24.
  • Johnson, D. A. 1994. Effect of foliar infection caused by Colletotrichum coccodes on yield of Russet Burbank potato. Plant Dis. 78:1075-1078.
  • Johnson, D. A., Alldredge, J. R., and Allen J. R. 1994. Weather and downy mildew epidemics of hop in Washington State. Phytopathology 84:524-527.
  • Miller, J.S., and Johnson, D.A. 2000. Competitive fitness of Phytophthora infestans isolates under semiarid field conditions. Phytopathology 90:220-227.
  • Johnson, D.A., Cummings, T.F., and Geary, B. 2000. Postinfection activity of selected late blight fungicides. Plant Dis. 84:1116-1120.
  • Johnson, D.A., Alldredge, J.R., and Hamm, P.B. 1998. Expansion of potato late blight forecasting models for the Columbia Basin of Washington and Oregon. Plant Dis. 82:642-645.

Johnson Hall 317A (office) &
Vogel Plant BioScience 127(lab)

Tel.: (509)335-3753
Fax: (509)335-9581



Epidemiology and Management of Plant Diseases – PlP 551. Principles and practical implications of plant disease epidemiology, disease management, and pathogen ecology. Examples of diseases caused by fungi, prokaryotes, viruses, and nematodes of crops grown in the Pacific Northwest and of international importance are used in discussions of the above topics.

Cooperative Extension Responsibilities:

Dieases of potato and mint in central Washington.s

Department of Plant Pathology, PO Box 646430, Washington State University, Pullman WA 99164-6430, 509-335-9541, Contact Us
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