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United States Department of Agriculture

Agricultural Research Service

Warren E. Copes

Research Plant Pathologist

Research Interests

My research focuses on integrated disease management (IDM) for regionally important diseases that are difficult to control in ornamental plant nursery production. My approach in selecting potential control options is to first consider what biological information may be lacking about the plant pathogen to change our status quo; second to evaluate relevant sanitation, cultural and chemical controls to verify efficacy; and third to determine what combination of controls provides the best balance of control and cost. IDM is justified when no single control works well.

Ornamental plant production is a complex cropping system. The industry markets a broad  diversity of horticultural plant selections and traits (environmental tolerance, flower color, plant form, etc.), often growing multiple cultivars of a single plant species. Disease tolerance is specific to each cultivar and a number of valuable cultivars have moderate disease susceptibility issues. In an IDM approach, sanitation and/or cultural management practices serve as a first line of defense to contain spread and create an environment unfavorable for disease development. Fungicides provide a second line of defense to reduce infection and/or development of inoculum. Disease control options should be flexible so producers can select based on efficacy and cost relative to the environment, disease problems and management styles of their production facility.

My five year project plan includes the following projects.



Objective 1.  Determine efficacy of disinfectant flow rates in irrigation water.

Approach.  Chlorine dioxide dose responses to control Phytophthora nicotianae will be evaluated under various water quality treatments in the laboratory, than validated in a field scale irrigation system.


Objective 2.  Determine seasonal dispersal of Phytophthora propagules in containment ponds.

Approach.  In-ground tanks will collect irrigation run-off from container-grown shrubs infected with Phytophthora species. The water will be monitored for the seasonal presence of Phytophthora propagules and be used to irrigate healthy container-grown shrubs.


Objective 3.  Evaluate seasonal treatment of irrigation water with disinfectants.

Approach. Seasonal treatment periods will be selected from the results in Objective 2. Seasonal and continuous water treatments will be evaluated by the severity of disease development.



Objective.  Evaluate preventive and reactive disease management strategies to control Pseudomonas, Colletotrichum, and Rhizoctonia in plant propagation facilities.

Approach.  Initially, single control methods will be evaluated in response to problematic dispersal mechanisms relative to each pathogen. A series of experiments will follow to challenge control adding complexity by integrating preventive and/or reactive disease management strategies.



Objective 1. Monitor seasonal and distance dispersal patterns of Passalora sequoiae spores.

Approach.  A 24-hour continuous Buchner air spore trap will monitor aerial spore dissemination. Intermittent 10-minute rotorod spore traps will be set out at regular intervals to a maximum distance of 100 meters. Healthy plants will serve as sentinel bait plants to monitor infection and will be swapped at regular intervals for new sets of healthy  plants.


Objective 2.  Evaluate timing of fungicide applications and pruning periods to control Leyland Cypress blight.

Approach.  Based on results in objective 1, fungicide timing strategies and pruning periods will be evaluated. Healthy and diseased plants will be placed in experiment plots and treated according to schedules. Disease development will be evaluated at regular intervals.



Objective.  Identify degree of fungicide coverage needed to achieve control and optimal nozzle patterns needed to achieve sufficient coverage in ornamental container-grown shrubs.

Approach.  1) Measure disease development of Rhizoctonia web blight on container-grown azaleas that have been sprayed with a range of fungicide coverage patterns to determine the level of coverage associated with no, low, moderate, and high levels of disease development.  

2) Compare flow rate arrangements of nozzle types and sizes, and tractor speeds with several types of commercial airblast sprayers to control disease across a 100 foot block of container-grown plants.

Publication Reprints

Journal Articles


·      Copes, W. E., Yang, X., and Hong, C. X. 2015. Phytophthora species recovered from irrigation reservoirs in Mississippi and Alabama nurseries and pathogenicity of three new species. Plant Disease 99: (accepted Feb. 26, 2015).

·      Copes, W. E. 2015. Spread potential of binucleate Rhizoctonia from nursery propagation floors to trays containing azalea stem cuttings and sanitary control options. Plant Disease 99: (accepted Nov. 12, 2014).

·      Copes, W. E. 2015. Weather-based forecasting of Rhizoctonia web blight development on container-grown azalea. Plant Disease 99:100-105.

·      Yang, X., Copes, W. E., and Hong, C. 2014. Two novel species representing a new clade and cluster of Phytophthora. Fungal Biology 118:72-82.

·      Copes, W. E., B. Barbeau, and G. A. Chastagner. 2014. Chapter 21. Chlorine dioxide. Pages 251-265 in: Biology, Detection and Management of Plant Pathogens in Irrigation Water. G. Moorman, C. Büttner, W. Wohanka, and C. Hong (eds.). APS Press, St. Paul, MN. 2014.

·      Elmer, W. H., Buck, J., Ahonsi, M. O., and Copes, W. E. 2014. Chapter 24. Emerging Technologies for Irrigation Water Treatment. Pages 289-301 in: Biology, Detection and Management of Plant Pathogens in Irrigation Water. G. Moorman, C. Büttner, W. Wohanka, and C. Hong (eds.). APS Press, St. Paul, MN.

·      Copes, W. E., and Benson, D. M. 2014. Rhizoctonia damping-off, stem canker and root rot. Pages 14-15 in: Compendium of Rhododendron and Azalea Diseases and Insects, 2nd edition. R. Linderman, and D.M. Benson (eds.). APS Press, St. Paul, MN.

·      Copes, W. E., and Benson, D. M. 2014. Rhizoctonia web blight. Pages 15-19 in: Compendium of Rhododendron and Azalea Diseases and Insects, 2nd edition. R. Linderman, and D.M. Benson (eds.). APS Press, St. Paul, MN.

·      Yang, X., Copes, W. E., and Hong, C. 2013. Phytophthora mississippiae sp. nov., a new species recovered from irrigation reservoirs at a plant nursery in Mississippi. Journal of Plant Pathology and Microbiology 4:5. doi:10.4172/2157.7471 1000180.

·      Copes, W. E. 2013. Rhizoctonia web blight development on azalea in relation to leaf wetness duration in the glasshouse. Journal of Phytopathology 161:723-729. 

·      Copes, W. E., Hagan, A., and Olive, J. 2012. Timing of fungicides in relation to calendar date, weather, and disease thresholds to control Rhizoctonia web blight on container-grown azalea. Crop Protection 42:273-280.

·      Clark, J. S., Blythe, E. K., Copes, W. E., Windham, A. S., Bost, S. C., and Windham, M. T. 2011. Growth sensitivity of Corynespora cassiicola to thiophanate-methyl, iprodione, and fludioxonil. Online. Plant Health Progress doi:10.1094/PHP-2011-0926-03-RS.

·      Copes, W. E., Rodriguez-Carres, M., Toda, T., Rinehart, T. A., and Cubeta, M. A. 2011. Seasonal prevalence of species of binucleate Rhizoctonia fungi in growing medium, leaf litter, and stems of container-grown azalea. Plant Disease 95:705-711.

·      Copes, W. E. and Blythe, E. K. 2011. Rooting response of azalea cultivars to hot water treatment used for pathogen control. Hortscience 46:52-56.

·      Copes, W. E., and Scherm, H. 2010. Rhizoctonia web blight development on container-grown azalea in relation to time and environmental factors. Plant Disease 94:891-897.

·      Ahonsi, M.O., Banko, T.J., Doane, S.R., Demuren, A.O., Copes, W.E., and Hong, C. 2010. Effects of hydrostatic pressure, agitation and CO2 stress on Phytophthora nicotianae zoospore survival. Pest Management Science (online journal) DOI 10.1002/ps.1926.

·      Copes, W.E., and Blythe, E.K. 2009. Chemical and hot water treatments to control Rhizoctonia AG P infesting stem cuttings of azalea. HortScience 44:1370-1376.

·      Thomson, J.L., and Copes, W.E. 2009. Modeling disease progression of camellia twig blight using a recurrent event model. Phytopathology 99:378-384.

·      Copes, W.E. 2009. Rate and intervals of hydrogen dioxide applications to control Puccinia hemerocallidis on daylily. Crop Protection 28:24-29.

·      Copes, W.E., and Thomson, J.L. 2008. Survival analysis to determine the length of the incubation period of camellia twig blight caused by Colletotrichum gloeosporioides. Plant Disease 92:1177-1182.

·      Copes, W.E., and Stevenson, K.L. 2008. A pictorial disease severity key and the relationship between severity and incidence for black root rot of pansy caused by Thielaviopsis basicola. Plant Disease 92:1394-1399.

·      Rinehart, T.A., Copes, W.E., Toda, T., and Cubeta, M.A. 2007. Genetic characterization of binucleate Rhizoctonia species causing web blight on azalea in Mississippi and Alabama. Plant Disease 91:616-623.

·      Copes, W.E., and Scherm, H. 2005. Plant spacing effects on microclimate and Rhizoctonia web blight development in container-grown azalea. HortScience 40:1408-1412.

·      Copes, W.E. 2004. Dose curves of disinfestants applied to plant production surfaces to control Botyrtis cinerea. Plant Disease 88:509-515.

·      Copes, W.E., Chastagner, G.A., and Hummel, R.L. 2004. Activity of chlorine dioxide in solution of ions and pH against Thielaviopsis basicola and Fusarium oxysporum. Plant Disease 88:188-194.

·      Copes, W.E., Chastaganer, G.A., and Hummel, R.L. 2003. Toxicity responses of herbaceous and woody ornamental crops to chlorine and hydrogen dioxides. Online. Plant Health Progress (online journal) dol:10.1094/PHP-2003-0311-01-RS.



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Last Modified: 5/18/2015