War of the Roses:
A Case Study In Plant Pathology

by
Melissa B. Riley
Department of Plant Pathology and Physiology
Clemson University

Jason headed home with a pile of dirty clothes for his mother to wash. The previous week had been hectic, with an exam in entomology, a homework assignment in plant pathology, and an exam just today in plant physiology. All he wanted to do over the weekend was relax. As he pulled into the driveway, he wondered what was for supper.

"Mom?" yelled Jason as he opened the front door. "Where are you?"

"Out here," came a faint response from the back yard.

As Jason walked out to the back deck, his mother, Mrs. Cook, continued: "Something is wrong with my rose bush next to the deck and I need to know what to do about it."

Jason bent over the rosebush his mother was pointing to. "Look at this," she complained. "They looked beautiful just a couple of months ago and now, just look. I have lots of these black spots on the leaves. After the leaves get these black spots, the spots get larger, and then leaves turn yellow and eventually start to fall off. If this continues, it won't be long before there won't be any leaves left."

Jason tried to remember if they had discussed roses and their diseases in his plant pathology class.

Mrs. Cook continued on her tirade. "You're taking a course on plant diseases this semester, aren't you? Haven't you learned anything that you can use?"

"Mom, I'm not interested in diseases of ornamental plants. I'm getting a degree in turfgrass management. I'm interested in diseases that occur on grasses and lawns."

"Don't golf courses have flowers around them that you'll have to maintain?" asked Mrs. Cook.

"Yeah, they do have flowers and other ornamental plants, but most golf courses have someone hired to maintain the ornamentals around the golf course. I'm not planning on working with that part of the industry."

"But don't you think you ought to know something about other plants even if it's just to keep the plants around your mother's house healthy?" complained Mrs. Cook as she walked across the yard. "Look at this rose bush. It looks fine. I haven't treated this plant any differently from the other one. The two plants got the same amount of fertilizer and water."

Jason sighed and said, "OK, Mom. I'll try to find out what is wrong with your roses and what you can do to control the problem. I can contact someone at State University when I get back on Monday, or I'll look up some information for you."

Jason remembered that there was a Plant Problem Clinic back at State University and that he could send a sample there.

On Monday after Jason returned to school he went by the Plant Problem Clinic and got the form (see Appendix A) he needed in order to submit a sample of his mother's roses to the clinic. He hoped that he could get a quick answer to his mom's problem. As he looked at the form he was overwhelmed by the amount of information it asked for and he started to wonder if the problem with his mother's roses was really worth the hassle.

Questions for Consideration

1. What is meant by symptoms and signs of plant diseases? What do these terms refer to and why are they important?
   
   
2. Describe the symptoms/signs of the rose plant provided in lab that was seen by Jason in Mrs. Cook's yard. How can the microscopic observations be important? (Samples should be observed utilizing compound and dissecting microscopes. Using the directions included in the case study in Appendix B, students should make tissue mounts to look for the presence of spores on the leaf surface.)
   
   
3. What are some questions that Jason should ask his mother concerning the care and culture of her roses? Why are these questions important?
   
   
4. Try to answer the questions on the plant problem clinic form. Why are these questions important?
   
   
5. Is the problem found on the rose a disease, insect, or physiological/cultural problem? What is the basis for your answer? Are you positive? Why or why not?
   
   
6. Where would you find information on the diseases associated with roses, both on the Internet and in printed resources? Give three sources of information, at least one from Internet sources and at least one from printed resources.
   
   
7. Based on the information that you have obtained, what is possibly affecting Mrs. Cook's roses? Is this the only possibility? Why or why not?
   
   
8. What are the possible reasons why the problem is not occurring on the other rosebush in the yard?
   
   
9. If you were Jason, what kind of recommendations would you make to your mother? What are the advantages and disadvantages of the different measures? Would what you recommend be different if you were talking to a commercial grower of roses? Why or why not? What would you do if your mother does not want to use any chemical treatment measures?
   
   
10. What are the differences between diagnosing a plant disease and a human disease? Is it more or less difficult to diagnose a plant disease?

Date Posted: mb 05/03/01
Image Credit: Rosa centifolia foliacea, by Pierre Joseph Redouté. Courtesy of The Herbarium at The Garden Link.