Objectives of this case

After completing this case study, students will further develop the following knowledge and skill sets:

1. Knowledge about factors a grower should consider when a problem arises in a production setting

2. An understanding of the diagnostic process for disorders incited by environmental, disease, or nutrition problems

3. Appreciation for the limits of time and money when seeking solutions to a problem

4. Confidence to work through the diagnostic process, sometimes with limited knowledge about the cause of a problem

Ancillary objectives of this case study that the instructor may have include the following:

1. An introduction to niche marketing concepts such as forcing specialty cut flowers

2. A discussion of appropriate nutrient analyses techniques, which depend upon the root medium used for production

3. An understanding of options and procedures for plant disease diagnosis

The decision case

Note that the case-study text and other tools, such as video clips and Web links to external resources that augment presentation of this decision case, are available to students and instructors (Spaw et al., 2004a).

The grower, Maria Flint, is forcing dicentra for the first time as a cut flower crop for Valentine's Day sales. Although dicentra is common in spring perennial gardens across the central Great Plains, it is not often found as a cut flower crop. Because it blooms from late April until early June under natural environmental conditions, it must be forced into flower for Valentine's Day sales. However, with arching racemes of delicately formed heart-shaped flowers from which it takes its common name, bleeding heart, it is an appropriate crop for the Valentine's Day market.

Flint's Flower Farm specializes in the production of unique cut flowers for local markets in Lincoln and Omaha, NE. The flower farm is located between these two population centers in Cass County in the eastern third of the state, and the farm falls at 41°N latitude. Flint's Flower Farm produces cut flowers in the field, in high tunnels, and in one heated greenhouse, so production and cash flow is year-round. The farm uses municipal water for irrigation.

Although dicentra can be produced from seed, this species is typically grown from crowns for cut flower production. For cut dicentra stems to be ready for harvest by Valentine's Day, a 5- to 8-week cropping cycle is recommended (Smith, 2001). Maria purchased her dicentra crowns from a major supplier of perennial plants for the nursery industry. She planted the crowns on 18 Dec. in 1-gal black plastic nursery pots filled with a pasteurized soilless medium of 2 peat : 1 perlite : 1 vermiculite (by volume) that had been amended with dolomitic lime to adjust the pH to within the recommended range of 7.0 to 8.5. The pots were set on a staggered spacing of 12-inch centers.

Growing temperature was 70 °F day and 55 °F night in the farm's single heated greenhouse structure. Three weeks after the crowns were planted, fertilization began with 200 ppm N from 15N–7.0P–14.1K (15–16–17 Peter's Peat-Lite Special Fertilizer; The Scotts Miracle-Gro Co., Marysville, OH), which was applied at every watering through a 1:15 Hozon proportioner (Phytotronics, Earth City, MO). The plants were watered two to three times per week. Yellow sticky cards were placed throughout the crop to monitor for flying insect pests as part of a scheduled scouting program throughout the production cycle. The crop was not sprayed with any pesticides or plant growth regulators. Very little information is known about forcing dicentra, but Maria was able to find a useful extension publication that guided her production strategy (Smith, 2001).

On 23 Jan., Maria noticed subtle chlorosis appearing on about a third of her dicentra crop. It tended to be interveinal and did not quite reach the leaf margins. In general, it was the older leaves that were exhibiting this disturbing chlorotic discoloration. Maria frequently visits with an extension horticulturist about production and marketing ideas. This contact is also valuable when problems arise. Maria is able to explain the situation during a phone conver-sation.

Excerpts from a phone conversation with an extension horticulturist on 23 Jan.:

EXTENSION HORTICULTURIST (EH): Okay, you have described some of the basic production practices for your cut dicentra crop, but I think I need to hear a little more detail about the symptoms. Slight yellowing of the foliage can be caused by a lot of things and it is difficult to diagnosis the cause without a picture or an actual plant; even then, it can be tough.

• MARIA (M): Yes. I just want to pick your brain and kind of run through the list of possibilities.

• EH: Sure. Categories of potential problems boil down to nutritional, environmental, insect, or disease, or even a combination of these. Let's try to rule out some of these as causes as the starting point to get to the bottom of what is really going on.

• M: Good plan. Well, the chlorosis is subtle and it is not even showing on all of my plants.

• EH: Do you see patterns of affected plants, for example, in one section of the greenhouse or on one bench, or is it pretty randomly distributed throughout the crop?

• M: I would say that it is random … showing on plants here and there, but no definite pattern.

• EH: How do the roots look? To the edges of the pot? White or brownish?

• M: You know, I really have not checked the root system yet.

• EH: Do go ahead and knock several plants out of the pots to check on the root system. Good roots grow good shoots, so you will want to get in the habit of checking root systems routinely. What about any insect problems?

• M: I have been scouting regularly. I put out yellow sticky cards and do counts of what I trap on a weekly basis, even though it can be hard to find the time to do that sometimes. Fungus gnats (Bradsydia spp.) and shore flies (Scatella spp.) have been a nuisance throughout the crop, but I am not seeing anything else that concerns me at this point. No thrips (Thysanoptera), whiteflies (Aleyrodidae), aphids (Aphididae). Nothing else.

• EH: That is all good news. Let's talk a little more about nutrition, then. You said that you are fertigating with 15–16–17 Peter's Peat-Lite Special, applying 200 ppm N … and you added no other preplant amendments except for the dolomitic lime. The symptomology of chlorosis would be consistent with deficiency of a handful of nutrients, especially with you catching the problem this early. It is less likely a toxicity problem, though that is a possibility as well. It is really hard to tell when the plants are just starting to express a problem. Do you know what your root medium pH and electrical conductivity (EC) are? That information would shed quite a bit of light on the situation.

• M: I have not run those tests on this crop, but I can do that and get back to you.

• EH: Great! Electrical conductivity will give us an idea of how much fertilizer is available to the plant. If it is really low, that may indicate a general nutrient deficiency that may be traced to a fertilizer injector not working properly or something along those lines. If the EC is very high, that may indicate salt toxicity that has burned the roots, and when roots cannot take up nutrients, the symptoms often manifest themselves as nutrient deficiencies. Now pH can be a little more complicated. If it is on the high side, that could mean that your micronutrient cations like iron, manganese, zinc, and copper are not readily available … and iron deficiency often appears as interveinal chlorosis of the upper leaves. If the pH is on the low side, perhaps magnesium or calcium is beginning to be tied up. Magnesium deficiency often appears as interveinal chlorosis of the lower leaves.

• M: Do you think that I should do anything at this point … spray something?

• EH: Well, we really do not have much information to go on at the moment. We have not ruled out nutrition, or disease, for that matter, as a source of the problem. You would be fine to continue fertilizing at each watering. Because the symptoms remind me of calcium deficiency as much as anything else, you could even apply a one-time drench of flowable dolomitic limestone (calcium and magnesium carbonate) if the pH turns out to be a little low. In that case, even if calcium deficiency is not related to the problem, the drench will not hurt the crop.

Twelve days later, as Valentine's Day neared, the chlorosis continued to worsen and younger leaves were beginning to wrinkle, pucker, and exhibit slight chlorosis as well. Maria needed to figure out quickly what was causing the disorder because she did not know if it would impact development of the bleeding heart flowers for which she had already lined up Valentine's Day sales. In addition, she wanted to identify the problem so that she could avoid it in the future.

Your assignment is to put yourself in Maria's shoes: Decide what test(s) you would run to sort out the problem. Justify your decision to run each test and keep track of the costs by completing the TMBF. The goal is to solve the problem while spending the least amount of money, but time is of the essence because the market date is nearing and the symptoms of the disorder are worsening.

The starting point is to determine what the crop's history reveals about the problem. Chlorosis can be incited by many things, certainly, but you can glean several probable leads from what is known. What information do you need to validate or eliminate a particular known cause of the type of chlorosis described?

The “diagnostic action chart” (Fig. 2) provides the means, via the website, to gain additional information to solve the problem. For example, the diagnostic action “plant tissue analysis” (Fig. 3) provides information about how to sample tissue properly, analytical techniques, and test results as well as standard acceptable ranges. Some information can be gathered quickly “in-house” by Maria herself whereas other information may be provided as test results or from a conversation with an expert in the field. Answer the questions on the TMBF to justify your conclusions.

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A screen shot of the website that contains the “diagnostic action table” is provided. The table provides information about each diagnostic action: whether it is performed by the grower or outsourced, the cost incurred, and the time involved to complete it. More information can be gathered by clicking on the specific diagnostic actions. This exhibit is available as a part of the website (Spaw et al., 2004a).

Citation: HortTechnology hortte 18, 1; 10.21273/HORTTECH.18.1.168

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The “plant tissue analysis” diagnostic action contains information about the procedures for plant tissue sampling as well as test results and acceptable ranges of tissue concentrations for the sample of dicentra submitted. This exhibit is available as a part of the website (Spaw et al., 2004b).

Citation: HortTechnology hortte 18, 1; 10.21273/HORTTECH.18.1.168

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Interpretive or teaching notes

The teaching notes are located at the same website as the case study; however, it is a hidden link (Spaw et al., 2006a). Presumably only the instructor would gain access to this link, which provides further explanation, discussion aids, and solution of the case study. This case study is intended for upper-level under graduate courses of greenhouse management, plant pathology, floriculture production, and nutrient management.

Contingent on the course objectives, size of the class, and instructional style of the educator, this case may be tailored to fit the specific needs of a course. It may be assigned to individuals or as a group project, either outside of class or during class time. Ideally, a designated computer laboratory would be available for those who may not otherwise have access to a computer. For example, an instructor may choose to combine the assignment of this case study and its discussion with a laboratory to instruct techniques of in-house root medium testing or use of simple ImmunoStrip test kits (Agdia, Elkhart, IN) for virus testing. Both procedures are explained within the case study.

The questions on the TMBF require students to justify their conclusions. Having the students explain how they arrived at their particular diagnosis reveals their true understanding of the situation (Stewart, 2004) and helps them delineate the process that they went through to come to a decision. The 2004–2005 TMBF questions were framed so the students’ focus was finding a solution (Table 1). The TMBF was changed in 2006 (Fig. 1) to encourage students to focus on the process of crop diagnosis instead of formulating a premature solution (Table 1).

Table 1.

A comparison is shown of questions on the 2004–2005 “time and money budget form” (TMBF) with those on the revised 2006 TMBF.

View Table

Additional questions that may elicit some discussion include the following:

1. Reflecting on your first impression, what was your initial thought about what might be wrong with the dicentra?

2. What steps of the diagnostic process helped you confirm or decide against your initial impression?

In addition to presenting an opportunity for class discussion of the problem and the diagnostic process, discussion could be focused in a number of ways.

Closure: Diagnosis of the problem and what Maria did

The plant disorder was determined to be tobacco rattle virus [TRV (tobravirus)]. The virus was identified when an extension plant pathologist compared symptomatic foliage with an image posted to the Web (Lane, 2006). The diagnosis was confirmed by sending tissue to Agdia and specifically requesting an assay for TRV, a virus that is not included in the results of the “ornamental screen” presented in the case study. Therefore, students did not have these results available to them in the diagnostic action chart because additional work by the extension plant pathologist was required after the initial, general virus screen. This may contribute to frustration for the students as they work to complete the case study, but it provides an opportunity for discussion to reveal how the extension pathologist continued the diagnostic process after the initial road block: She went to the Agdia website (Agdia, 2006), noted other ornamental viruses, conducted a Web search using keywords “dicentra” and “tobacco rattle virus” (as well as other general ornamental viruses), came upon a photo that matched the symptoms, and confirmed her diagnosis by sending a second sample to Agdia with the specific request to test for TRV.

Tobacco rattle virus is spread by trichodorid nematodes and is normally restricted to roots. Dicentra is one of the few plant species in which the virus becomes systemic. Because the virus is spread by nematodes, it was determined that infected crowns must have been shipped to Maria. The supplier was contacted about the TRV-infected plants and they indicated that they were aware of the industrywide problem but their root stock, received from Europe, was also often infected. They did not indicate if they routinely screen for the virus.

Maria harvested all the cut stems that she could, taking care not to spread the virus from infected to uninfected plants. She culled all the plants that were showing symptoms of TRV. Because this was a new crop for her, it was unclear whether her stem yield was dramatically affected. In the future, Maria intends to order rootstock from another supplier to determine whether this helps alleviate the virus problem.

Student feedback on use of case study

Students in four floriculture production classes over 3 years—three classes at Kansas State University (KSU) and one class at University of Nebraska–Lincoln (UNL)—were asked to respond to pretest and posttest questionnaires about the dicentra case study. The questions assessed perceived value of the case study as well as confidence in completing the diagnostic process (Tables 2 and 3). All data were analyzed using the nonparametric Mann-Whitney statistical procedure and Exact tests of SPSS (Graduate Pack, 11.5 for Windows; SPSS, Chicago). Exact tests is an SPSS software addendum that calculates exact P values for small and nonuniformly distributed data.

Table 2.

Means of student responses to statements about their use of the dicentra case study from the pretest and posttest questionnaire.

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Table 3.

Means of student opinions about the dicentra case study.

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Comparison of 2004–2005 posttest with pretest student responses shows a general trend of increasing confidence in diagnostic procedures after the completion of the case study (Table 2): In 2004, both KSU and UNL student groups reported a significant increase in understanding the diagnostic options and procedures (Table 2, H). In addition, UNL 2004 and KSU 2005 both reported a significant increase in understanding the difference in soil testing between agronomic crops and ornamental crops (Table 2, G), which is a unique focus of the case study. Furthermore, in KSU 2004 and KSU 2005, a significant increase in confidence was reported in ability to complete the diagnostic process after completing the case study (Table 2, B).

An exception is that all student groups trend toward less understanding about the damage incited by insect (arthropod) pests. This may be attributed to the lack of focus on arthropod pests in the dicentra case study: The grower reports no significant insect infestations. During group discussion, the solution revolves around nutrition and viral diseases, not insects.

Group discussion enhances learning if students are permitted to discuss problems, solutions, and explanations that they have generated (Gall and Gillett, 1980). With the dicentra case, all groups recognized that for the case to be effective, a group discussion was necessary (Table 3). All student groups were in agreement that the solution to the case was unexpected (Table 3). This speaks to the complicated nature of this case study. The balance needed when using the case study method is creating enough cognitive dissonance to cultivate learning without fostering frustration. Cognitive dissonance is commonly resolved when the student processes new information to make a decision, but because a straightforward solution is not obvious from the background information provided in this particular case study, the class discussion is an integral part of the resolution process.

In 2006, the TMBF was modified by changing the student response questions (Table 1) to improve development of problem-solving skills. The solution-based questions of the 2004–2005 TMBF required students to specifically identify the cause of the chlorosis. With this focus, students scramble for an answer that is most likely to maximize their grade (Johnson et al., 2002). This contributes to overconfidence, which masks the need for new information to determine an accurate solution (Blanton et al., 2001). One way to avoid overconfidence is to require students to focus on process rather than solution. With the process-based questions of the 2006 TMBF, students must define information needed to proceed, which is a major objective of case studies (Johnson et al., 2002).

Although this change to the 2006 TMBF did not contribute to a trend of significant increase in student confidence in their diagnostic skills, it can be argued that refining problem-solving skills is an appropriate goal late in the undergraduate's educational career. Case studies, with process-based assessment and group discussion, provide a means to develop problem-solving skills, which is an elusive but often sought-after characteristic by their future employers (e.g., Berle, 2007).

The dicentra case study was developed for advanced students with previous exposure to the case study method. Student assessment data indicate that students can substantially benefit from the experiences of working through this complicated case study. All student groups felt that solving the case study was a worthwhile exercise (Table 3). Students acknowledged their role as a decision maker, which is a goal in learning processes using a case study (Hoag et al., 2001). The dicentra case study is a novel learning tool that can be used to minimize student overconfidence while developing and refining more advanced problem-solving skills.