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Worms in the Grass: A case study concerning the extraction and identification of plant-parasitic nematodes

Melissa B. Riley and Paula Agudelo
Department of Entomology, Soils, and Plant Sciences
Clemson University
mbriley@clemson.eduand pagudel@clemson.edu

THE CASE

Bennett looked at the grass samples collected from the greens and fairways of the 16th, 17th, and 18th holes of the Sencopia Golf Course, near Burton’s Neck. They did not look healthy at all. The grass appeared to be somewhat yellow in spots (Figures 1 and 2). It had been fertilized at the rates recommended based on the soil testing done earlier in the year. Other greens on the golf course appeared healthy. The areas had been previously fertilized based on the soil testing done earlier and the watering was essentially the same. He was at a loss to determine why the grass did not appear healthy. The symptoms were in a random patchy pattern and they had become more apparent since the turf had come under the stress of high summer temperatures. He pulled up some grass seedling from the affected greens and did not see many roots, and those he saw were discolored, especially when compared with the seedlings from unaffected greens (Figure 3). He did not observe any fungal growth on the roots that were present; there just weren’t many roots. Since Bennett did not know what might be wrong he decided to call his friend Gregory to see if he had any suggestions.

Gregory is in graduate school at Clemson University and his research involves testing new turfgrass varieties for their resistance to nematodes. He had worked with Bennett on the golf course at Clemson University when they had been undergraduate students. Bennett hoped his friend would be able to help him determine what was wrong. Bennett knew his job was in jeopardy. He had been the course manager less than 6 months and if he was going to maintain his job, he better determine what the problem was and fix it as soon as possible. He had a meeting with the review board for the course next Friday and he knew that they would have questions about the appearance of the grass.

Bennett took some digital photographs of the greens and fairways (Figures 1-2) and what the grass looked like when he pulled it up (Figure 3) because he knew that Gregory was sure to say that he could not diagnose Bennett’s problem over the phone and needed more information. After taking the pictures he went back to his office and sent a message to Gregory along with the pictures. Thirty minutes after sending the message Bennett decided that he would follow up on his message with a phone call to Gregory.

Gregory answered his phone after the third ring. “Hello, this is Gregory”.

“Hey Gregory, this is Bennett. I need help. I am afraid that if I don’t solve my problem or at least determine what the problem is my 6-month trial as the golf course manager will be just that - 6 months. I have problems with three of my greens and adjacent fairways. They are chlorotic and spotty in appearance. We applied fertilizer based on our soil testing two months ago. When I pulled up some of the chlorotic grass the roots did not look healthy. In fact the grass was easy to pull up because there were hardly any roots. The roots however don’t appear to have any fungal growth on them and I have been applying fungicides to control the major fungal diseases.”

Gregory wondered how he had gotten to be Bennett’s problem solver. He was trying to graduate and was overwhelmed with all that he had to do before graduation. He knew the major diseases of turfgrass of golf courses since he had done summer internships at Pinehurst Golf Course in North Carolina and Augusta National in Augusta, Georgia while he was an undergraduate student. He also knew about nematode damage on turfgrass because his graduate research focused on evaluating turf varieties for nematode resistance. However, he hated to diagnose diseases over the phone without plants to look at and without being able to see the overall symptoms. He had found that often when a person described symptoms over the phone they would not provide adequate descriptions or would often leave out major observations. While working on his graduate degree, Gregory accompanied his advisor on numerous occasions and he had witnessed many problems that could occur on golf course turfgrass. Sometimes the problems were not due to any pathogens at all, but were environmental and cultural problems.

“You know it is hard to diagnose disease problems over the phone.” Gregory started.

Bennett quickly interrupted, “I knew you wouldn’t believe it unless you saw it. So I sent you some pictures of the overall appearance of the grass as well as pictures of the roots of affected and healthy plants. I sent them to you about 30 minutes ago so you should have gotten them.”

“OK, let me check my e-mail account. I have been busy writing up my research this morning and have not checked my e-mail recently. OK, here is your message.”

Gregory quickly looked at the pictures. The grass was definitely not looking good – with a general chlorotic appearance. The chlorosis was more prevalent in some areas than in others. He looked at the pictures of the roots. He then thought of the diseases that occurred on golf courses and decided that they did not really fit the symptoms that Bennett was observing. Another thought quickly came to mind. Although he thought Bennett would have already considered it, he thought he better ask. “Have you had the soil tested?”

“What do you mean have I had the soil tested? I had it tested to determine how much fertilizer we needed to apply.” Bennett replied.

“I don’t mean that type of testing. Did you have it tested for nematodes?”

“Nematodes? Aren’t those worms of some type? Couldn’t you see them if they were on the roots. Don’t they produce galls on the roots or cysts?”

Gregory sometimes wondered about the classes Bennett had taken in college before he got his current job. “Not all nematodes cause galls or cysts and you cannot observe some of them on roots without a microscope. They can cause severe problems on greens. You need to send a soil sample to a nematode assay laboratory to determine if they could be causing your problems. Once you have the assay done you can determine what to do next.”

“Gregory, do you think that you could run a quick sample for me? Seems like I remember hearing that there aren’t many places that do nematode assays of soil samples.”

“OK, send me a sample and I will try to look at it for you but you are going to owe me big time.”

“Thanks, Gregory. I will take a sample right away and send it to you overnight express mail” Bennett replied.

Gregory quickly cut into the conversation because he was afraid that Bennett might be hanging up the phone, “By the way, do you know how to take the sample for nematode analysis? You don’t just want to take a sample from one area. I will send you an article that discusses the best way to sample an area for nematode detection.” Since Bennett had not considered the possibility of nematodes, Gregory was willing to bet that Bennett did not know how to take the sample.

“Hey thanks, I probably do need some information on how to take the sample. Do I need to take a sample from the greens that appear to be healthy?”

“It would probably be a good idea. You need to pull several samples but I don’t have time to do them all. I will only do two samples for you. You need to send the other samples to a nematode assay laboratory.”

“That sounds like a deal. I better go get the samples so they can go overnight express and you can get them tomorrow. Again, thanks for all the help.”

Questions for consideration (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)

  1. What are nematodes? Describe their general characteristics. Why can they be problems on many different plants including grass on golf courses?
  2. What are the general symptoms of nematode damage that can be observed on golf courses? Why are these symptoms present? When are the symptoms most commonly observed and why?
  3. How should Bennett take samples of the greens to make sure to get a representative sample? Why is how the sample is taken so important?
  4. How can you differentiate a plant-parasitic nematode from a free-living nematode in a soil sample extract? Why is this important?
  5. What types of nematodes are known to be problems on golf courses? List them and describe how they can be distinguished from each other.
  6. Look at the sample that you obtained from the Centrifugal-Flotation method using dissecting and compound microscopes and identify and draw at least three different plant-parasitic nematodes that are present. Could these nematodes be causing the problems with the grass?
  7. What are possible measures that Bennett can implement to manage nematodes on his golf course if they are present? What are the advantages and disadvantages of the different measures? How would you decide what methods to use in this situation (remember people are playing golf on this course every day)?
  8. What would you recommend to Bennett based on the analysis of your soil sample? Justify your answer based on the information that you have obtained from your sample in the laboratory.

References/Reading material to review prior to class

Lambert, K. and S. Bekal. 2002. Introduction to plant-parasitic nematodes. The Plant Health Instructor. DOI:10.1094/PHI-I-2002-1218-01.

Martin, B. and J. Golden. 2000. When dealing with turf problems in the Southeast – Don’t forget the nematodes. http://virtual.clemson.edu/groups/turfornamental/tmi/insectmanage/nematode.htm

Nematode Problems in Home Lawns. http://hgic.clemson.edu/factsheets/HGIC2154.htm

Tarjan, A.C., R.P. Esser, and S.L. Chang. Interactive Diagnostic Key to Plant Parasitic, Free-living and Predaceous Nematodes http://nematode.unl.edu/key/nemakey.htm