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Hosta Takeover: A Plant Disease Management Case Study.

Brooke A. Edmunds, Paula H. Flynn, and Mark L. Gleason
Department of Plant Pathology
Iowa State University
Mgleason@iastate.edu

Edmunds, B.A., P.H. Flynn, and M.L. Gleason, 2003. Hosta Takeover: A Plant Disease Management Case Study. The Plant Health Instructor. DOI:10.1094/PHI-T-2003-1222-01

INTRODUCTION

"Hosta Takeover: A Plant Disease Management Case Study" is based on a real-life situation and provides students experience making practical plant health management decisions. In this case, students are challenged to devise a disease control recommendation plan for Johnson Nursery, a company that is experiencing losses from a disease called hosta petiole rot. Unfortunately for the nursery, it appears that it shipped diseased hosta plants to some of its wholesale customers. As students study the details of the case, they will likely discover that finding a balance between company profit and careful plant disease management can sometimes pose ethical and economic dilemmas.

This case study has been used at Iowa State University in both an undergraduate plant-problem diagnosis course and an undergraduate plant health management course. The classes were composed of upper-level undergraduates majoring in horticulture, agronomy, and plant health and protection. The case study also would be appropriate for introductory plant pathology, sustainable agriculture, or integrated pest management courses.

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CASE OBJECTIVES

• Illustrate the basic plant pathology concepts of the disease triangle, methods of disease spread, and disease control practices.
• Devise a plant health management plan for a commercial nursery that is experiencing problems with a soilborne plant pathogen.
• Consider the economic and ethical issues involved in deciding whether or not to ship potentially diseased plants to customers.
• Prepare written and verbal disease management recommendations.
• Discuss how plant disease management practices may differ when comparing a commercial situation to a home-gardener situation.

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CAST OF CHARACTERS

Michael Hazen: the field supervisor in charge of nursery production for Johnson Nursery. He is responsible for disease, insect, and weed management along with general nursery activities such as planting, harvesting, and preparation of plants for sale

Jerry Mullen: the owner of Jerry's Garden Center, who is accusing Johnson Nursery of shipping him diseased plants

Laura Simpson: a consultant specializing in plant disease diagnosis who provided the disease cycle information and a list of disease management techniques

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THE CASE
Click here to go to the case study information for students.

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CLASSROOM MANAGEMENT

Case Summary

The focus of the case is how to manage hosta petiole rot at Johnson Nursery. Since hosta sales comprise a significant portion of the nursery's income, and the disease also can affect other herbaceous nursery crops, it is critical for the nursery to stop the spread of the disease. Sclerotium rolfsii var. delphinii, a fungal pathogen with a wide host range, could pose a significant risk to the company's profits. In addition to the immediate concern at the nursery, the manager must address complaints of a nursery dealer. To keep customers, Johnson Nursery must take measures to ensure that the stock it ships is free of the petiole rot pathogen.

Click here for a Powerpoint presentation of the images in the case study.

Suggestions on how to use this case

We found that class discussion works well in exploring the various issues of this case. The discussion and classroom activities can be completed in a 1-hour period, but a longer laboratory period is preferable, especially if photos of disease symptoms and field symptoms are projected and discussed.

On the day the case is discussed, it is helpful to provide a brief introduction to the Johnson Nursery hosta situation and review some of the main details. Introducing the cast of characters can help the students clarify the situation. This is a good time to discuss the suggested Introductory Questions. These questions should largely be a review of the reading, so they will help prepare students to participate in the discussion. The "Information on the ecology and management of petiole rot caused by S. rolfsii var. delphinii" also can be distributed.

After reviewing the details of the case, we ask the students to work in teams of three or four to devise a set of management recommendations for Michael Hazen. In addition to developing a bulleted list of practical recommendations that takes into account time and economic constraints, we also encourage the students to think of other creative solutions that might require research to determine feasibility. We give the students about 15 minutes to discuss their ideas. A group leader writes the recommendations for his or her group on the board. Depending on the class and group size, you may have several sets of group recommendations on the board to discuss. As the group leaders verbally present the recommendations, students and the instructors can ask questions or add comments. It usually becomes apparent that some groups are risk-takers, and others are more conservative. Some of the suggestions given in previous classes have included a bit of humor, such as using a high-powered vacuum cleaner to suck the sclerotia from the field.

You may wish to use a follow-up assignment for this case study. Examples we have used include:

1. Have the students put themselves in the place of Michael Hazen and compose a response letter to Jerry Mullen, the nursery owner who accused Michael of shipping diseased hosta plants.
2. Ask the students to put themselves in the place of Michael Hazen and prepare a presentation for the Johnson Nursery CEO that explains the disease problem and includes recommendations for its management.
3. Ask students to provide a written discussion of how their management recommendations might differ if the problem occurred in the garden of an avid hosta gardener rather than in a commercial nursery situation.

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Possible adaptations

This case is easily adaptable and can be personalized to a specific classroom need. Different aspects of the case can become the focus of a short discussion, for example the ethical issues raised, economic aspects, or even basic plant pathology such as Koch's Postulates and the components of the disease triangle for less advanced students. Also, the parts of the case can be introduced to the students at different times. For example, to foster creative thinking, we withheld the "Information on the ecology and management of petiole rot caused by S. rolfsii var. delphinii" material until after the students had devised their own management schemes. However, other instructors may find that a better discussion results when students have a chance to review all the available information.

Information on the ecology and management of petiole rot caused by S. rolfsii var. delphinii. Click here for this information.

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DISCUSSION QUESTIONS

Introductory

1. What three factors, mentioned in the disease triangle concept, are necessary for a disease to occur?
2. What environmental conditions favor the development of petiole rot of hosta, caused by the fungus Sclerotium rolfsii var. delphinii?
3. What are major symptoms of the disease and main signs of the pathogen?
4. Discuss the various methods by which the pathogen can spread from plant to plant or from field to field.
5. What are sclerotia? Why do they make disease control difficult?

Challenge

6. What additional information might be helpful to you in developing your disease management plan?
7. How can nursery production methods affect disease management?
8. Sclerotium rolfsii var. delphinii has a wide host range. How will this characteristic influence disease management strategies?

Decision Forcing

9. Using the information from the case and your own personal experience from internships, jobs, or coursework, how would you manage the petiole rot problem in Johnson Nursery? What should be done this year? What management practices do you recommend for a long-term solution?
10. What ethical issues are involved in this case?

Answers to these questions are available to instructors in the password-protected section of this site. Any instructor is welcome to register for access. Click here.

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REFERENCES

Agrios, G. 1997. "Plant Pathology 4th ed." Academic Press, San Diego, CA. This textbook is a good reference for basic pathology concepts, especially the disease triangle.

Edmunds, B.A., M.L. Gleason, and S.N. Wegulo. 2003. Resistance of hosta cultivars to petiole rot caused by Sclerotium rolfsii var. delphinii. HortTechnology 13(2): 302-305.

Mullen, J. 2001. Southern blight, Southern stem blight, White mold. The Plant Health Instructor. DOI: 10.1094/PHI-I-2001-0104-01.

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