The overall goals of this case study are to help students become familiar with the “disease triangle” concept and learn how a disease-warning system uses basic principles of plant pathology to help growers minimize their use of fungicides. Students will be challenged to help Iowa strawberry grower Jack O’Neil decide whether or not to use the warning system on his farm. From this case study, the students will:
- describe the disease triangle concept and explain how it relates to real-world disease management tactics,
- understand the life cycle of the pathogen (disease-causing organism) of AFR, a fungus named
Colletotrichum acutatum, and how it causes anthracnose fruit rot (AFR), and
- examine the pros and cons of using a disease-warning system in a real-world situation.
CAST OF CHARACTERS
Jack O’Neil: A strawberry grower who owns Sunny Patch Farm in central Iowa; he grows 15 acres of strawberries. The most profitable segment of Jack’s business comes from “pick-your-own” customers who visit his farm to harvest their own berries. In addition, he sells pre-picked fruit at a local farmer’s market. In the last 2 years, many of his customers, responding to scary news reports about serious health and environmental risks of pesticides, have asked about – and even insisted – that Jack sharply reduce the number of pesticide sprays he applies. Since most of Jack’s pesticide sprays consist of fungicides, his customers’ concern has zeroed in on fungicides.
Anna Nasser: Jack’s neighbor, who told Jack about her own family’s concerns – as well as those of 30 additional families who are Jack’s customers – regarding pesticide use in his pick-your-own strawberry fields. Anna has even threatened to organize a customer boycott of Sunny Patch Farm if Jack does not respond quickly to their concerns.
Dr. Nancy Muller: An extension plant pathologist at Iowa State University who researches strawberry diseases and advises growers on disease management of fruit crops.
This case is intended to help undergraduate students grasp the basic principles of the disease triangle, how weather conditions affect plant disease risk, and how growers can use disease-warning systems to manage threatening diseases in a more efficient and environmentally friendly way. Students will learn these concepts while gaining a basic understanding of anthracnose fruit rot (AFR) of strawberry, a difficult-to-manage threat because the pathogen can remain hidden for long periods and then suddenly break out in devastating epidemics. In addition, the case exposes students to the challenges of disease management in a situation where customers and their families visit the farm, handle the berries with their bare hands, and often eat the fruit without washing them. The farmer in the case, Jack O’Neil, must keep AFR under control while somehow responding to his customers’ demands to use less fungicide. When extension plant pathologist Nancy Muller suggests using a disease-warning system to meet his needs, Jack needs to get up to speed quickly on this new approach before trying it. Students will place themselves in the role of Jack, the owner of Sunny Patch Farm, and propose their own management plan based on the information provided. Students will gain a deeper understanding of real-world disease management in a high-value fruit crop and will analyze information
to help Jack make decisions.
HOW TO USE THIS CASE
This case is designed for use in a single 50- to 90-minute class. We suggest that Part Ι, which concerns basic information explaining why AFR poses such a threat to Jack’s strawberries, be assigned reading that is completed before the class period. The background information provided, which briefly describes how AFR attacks strawberries, should also be read before the class session.
During the first part of the class, we suggest that the instructor share the Part I information and present a short summary of AFR using a mind map (Willis and Miertschin 2006). Each student can write down his/her own answers on the mind map before and during the instructor’s presentation. There are two mind maps designed for class use:
one for the beginner level , which gives students more guidance, and
one for the advanced level. There is also one intended for instructor use. After the review, the class can be divided into small groups (for example, 3 to 4 students each) to discuss their individual answers among themselves for a few minutes, after which a representative from each group can present the group’s consensus answers for Part I.
After reviewing the disease information and discussing Part Ι, students will be given 5 minutes to read Part ΙΙ and then discuss answers to Part II questions in their groups for 10 minutes. As with Part I, each group should come up with their answers and then share these with the entire class using the mind map. Evaluating Part II questions can also be assigned as out-of-class group homework, where students bring their group’s answers to the next class period to share with the entire class.
This case study can be used for classes in plant pathology, horticulture, sustainable agriculture, integrated pest management, plant health management, and agricultural education. The case focuses on managing a tough-to-control disease with less reliance on fungicide by using a weather-based warning system. To decide whether it makes sense to use the warning system, the students need to understand the grower’s farming environment as well as the advantages and risks of the warning system.
A short summary of AFR
The disease triangle: a basic principle of plant pathology
Campbell, C. L., and Madden, L. V. 1990. Introduction to Plant Disease Epidemiology. John Wiley and Sons. New York.
Damm, U., Cannon, P., Woudenberg, J., and Crous, P. 2012. The
Colletotrichum acutatum species complex. Studies in Mycology 73:37–113.
Louws, F., Ridge, G., and Harrison, J. 2014. Anthracnose Fruit Rot of Strawberry | NC State University. Online publication.
MacKenzie, S. J., and Peres, N. A. 2012. Use of leaf wetness and temperature to time fungicide applications to control anthracnose fruit rot of strawberry in Florida. Plant Dis. 96:522–528.
Peres, N. A., Timmer, L. W., Adaskaveg, J. E., and Correll, J. C. 2005. Lifestyles of
Colletotrichum acutatum. Plant Dis. 89:784–96.
Smith, B. J. 2008. Epidemiology and pathology of strawberry anthracnose: A North American perspective. HortScience 43:69-73.
Weir, B. S., Johnston, P. R., and Damm, U. 2012. The
Colletotrichum gloeosporioides species complex. Studies in Mycology 73:115-180.
Willis, C. L., and Miertschin, S. L. 2006. Mind Maps as Active Learning Tools. Consortium for Computing Sciences in Colleges 21:266–272.
Wilson, L. L., Madden, L. V., and Ellis, M. A. 1990. Influence of temperature and wetness duration on infection of immature and mature strawberry fruit by
Colletotrichum acutatum. Phytopathology 80:111–116.