Link to home

Ineffective Fungicides: A case study on problems in selection and use of fungicides for disease management.  Case part A

Melissa B. Riley

Department of Entomology, Soils, and Plant Sciences
Clemson University

Angie was really enjoying her summer internship in the Chesterfield country extension office working with Mr. Watson. Mr. Watson had been an extension agent in the state for 20 years and was an excellent supervisor. Last year Angie had wondered what her internship would be like, but so far she really enjoyed the work. Mr. Watson had allowed her to become actively involved in the problems that came into the office and as a result she had learned a great deal. The internship had provided her with an opportunity to see the numerous problems an extension agent has to deal with and the diversity of knowledge that an extension agent needs. It also had illustrated to Angie why her degree in Agricultural Education required so many different courses. A majority of the problems that she had seen this summer had been related to horse management. These problems were easy for Angie since she had grown up and worked as a teenager on a horse farm. However, this morning the problem was about peaches and Angie knew it meant more work for her. No easy summer day.

Mr. Jones, a peach grower in the county, had called Mr. Watson and said that he was considering suing the supplier from which he had purchased his pesticides. He reported that he had never had significant losses to brown rot in his peaches, but this year his losses were extensive. He said his neighbor had bought her chemicals from a different dealer and she did not have significant brown rot problems. Mr. Jones said that he and his neighbor had applied the same number of fungicides, four per growing season, and they had applied their fungicide sprays on essentially the same days. Since this was the case he had decided that his chemicals must be ineffective and he was thinking about suing his pesticide supplier. Mr. Watson had told Mr. Jones that he would come out to his orchard after lunch and to take a look.

After the phone call, Mr. Watson asked Angie to investigate the chemicals recommended for the management of brown rot. He also asked her to determine the recommended application rates for the chemicals used as well as how often they should be applied. The final facts he wanted were what chemical class the recommended chemicals belonged to, and if there were any reports of resistance problems. As Angie was gathering the information she wondered if the problem was related to material they had discussed in her plant pathology class last fall. When she walked into Mr. Watson’s office with the information he had requested, Mr. Watson said, “Hey Angie, sit down with me for a few minutes and tell me what questions we need to ask Mr. Jones this afternoon. You can go with me. It could be very interesting and you will see how extension agents often have to be detectives. Sometimes you have to do a lot of looking and asking questions to determine what the problem is. Once we determine the problem, we will also have to make some recommendations about what Mr. Jones needs to do in order to prevent a recurrence of his problem.”

“I look forward to going this afternoon. I’m required to do a presentation on the types of activities I was involved in during my internship in the fall, and this could be a good example,” replied Angie.

Questions Related to Case – Part A

  1. What is the causal agent of brown rot? How and where does the organism that causes brown rot survive from one season to the next season (overwinter)? What types of spores cause initial brown rot infections during a season? When and where (in what plant tissue) do these infections occur?
  2. What are the major disease management measures for brown rot of peaches based on reducing overwintering sources of inoculum?
  3. Can brown rot of peaches be managed strictly through the use of non-chemical measures? Why or why not? How do environmental conditions impact disease management?
  4. What chemicals are currently approved to manage brown rot of peaches? Are there important concerns with the use of any of these chemicals? What are these concerns?
  5. If you are going to use pesticides to manage brown rot of peaches, what are the important factors that you need to consider when deciding which chemicals to use? Why are these factors important?
  6. Outline questions Mr. Watson and Angie should ask Mr. Jones when they go to the orchard and packing house. Why do they need to ask each question? Based on the information you currently have, can you determine what is wrong with Mr. Jones’s disease management program?

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


Ritchie, D. F. 2000. Brown rot of stone fruits. The Plant Health Instructor.  Updated 2005.

2007 Southeastern peach, nectarine, and plum pest management and culture guide. Bulletin 1171. D. Horton, P. Branner, B. Bellinger and D. Ritchie, eds. (Updated annually. Sections important to case include: Management Guide, Resistance Management, Pesticide Characteristics and Restrictions sections)