Diseases are perhaps the most unusual and perplexing of the important pest problems affecting highly‑managed turf. As a result, diagnosing problems that may be caused by disease represents one of the more challenging exercises in turfgrass management.

Both weed and insect pests can be readily observed with the unaided eye. And insects or weeds, regardless of their stage of development, look much the same regardless of the environment in which they are found. Further, being readily visible, their appearance can be matched with the diagrams and photographs presented in diagnostic references.

Diseases, on the other hand, are caused by a wide variety of microscopic organisms, none of which are observable without the aid of a microscope. Further, the activities of these pathogens can be seen only indirectly, by observing the responses of the turfgrass plants they have infected.

Diagnosis is further complicated by the fact that the symptoms of infection by a particular pathogen may differ, depending on factors such as the species of grass infected, the height of cut, local environmental conditions, or the presence of other pests and pathogens. Among the more important factors affecting the expression of symptoms is the presence of chemical, physical, and biological stresses.

Disease diagnosis can be thought of as a process of elimination, in which the range of potential causes for the observed problem is carefully reduced to one. The sequence of steps one follows in diagnosing turfgrass diseases is designed to assemble evidence for and against possible causes for the observed problem. It is important, therefore, that turfgrass managers maintain accurate and complete records of both site management activities and the season's weather. When these two data sets are combined with careful observations of the turfgrass symptoms and direct observations of pathogen structures, establishment of associations between the disease and a causal agent is possible.

Turfgrasses, because they are perennial plants, develop long‑term associations with pathogens. In fact, in nearly all mature turfgrass plantings, individual plants are perennially infected with many, if not all, of the pathogens capable of causing disease on that particular grass species. This is the reason that symptoms of many turfgrass diseases are observed most frequently when turfgrass plants are under stress. It also further complicates disease diagnosis, since the presence of many turfgrass pathogens in a given sample makes reducing the probable causes of the symptoms observed to a single causative agent difficult.

Because of all of these difficulties, competent disease diagnosis requires considerable training and experience. Turfgrass managers often turn to academic experts to assist in the diagnostic process, coupling their expertise in the field with the academic's expertise in the diagnostic laboratory to establish the cause of the problem and to recommend and carry out appropriate control measures.

5.1.1 Importance of Correct Disease Diagnosis

Proper diagnosis is central to any successful turfgrass disease management program. There are a number of reasons for this. First, identifying the cause of any disease problem helps the turfgrass manager identify some of the conditions that may have fostered its development. In a sense, the diagnosis itself helps the turfgrass manager learn something about the biology of the causal agents, and how to limit their impact.

Second, many contemporary disease control strategies are quite specific, being effective against one disease, ineffective against others, and potentially making still other diseases much worse. For example, the mode of action of fungicides can be very narrow, affecting only certain groups of fungal pathogens. Inaccurate diagnoses could thus lead to the application of unneeded fungicides, the side effects of which could be damaging.

Third, the refinement of Integrated Pest Management (IPM) scouting and monitoring protocols to fit the situation at hand is dependent on accurate identification of turfgrass pest problems. This is easily accomplished for weed and insect pests, but has been problematic for diseases. Accurate diagnosis gives turfgrass managers the ability to map and measure specific disease problems so that more effective control strategies can be implemented. It also gives them the ability to establish the efficacy of control measures and assists in the prediction of future disease outbreaks.

5.1.2 Basic Analytical Processes in Disease Diagnosis

All disease diagnostic procedures follow a logical sequence of steps, designed to gather evidence sufficient for the elimination from consideration of potential causal agents. Both field and laboratory observations are used in assembling this information.

One of the first challenges to any turfgrass manager is to determine whether an observed problem is actually the result of a disease. Disease symptoms often appear remarkably similar to damage from noninfectious agents (insects, for instance) or from a variety of abiotic problems (such as localized dry spots). Sometimes, the characteristics of the damage can provide clues. The patch‑like appearance of symptoms, usually more apparent on close‑cut than on higher‑cut turf, may be indicative of a disease problem. Most known turfgrass diseases are caused by fungi. Since fungi tend to grow radially, many fungal pathogens cause circular patch‑like symptoms in turfgrass plantings. There are several turfgrasses diseases, however, that do not typically induce patch symptoms, and these are commonly confused with signs of other turfgrass problems. The following are the steps one usually would go through in diagnosing these and other turfgrass diseases.

STEP 1. Identification of Affected Grass Species and Cultivars

One of the first steps in any diagnosis is to determine specifically which plants are affected. A number of turfgrass pathogens are relatively specific to particular turfgrass species, some even to individual turfgrass cultivars within a species. Take‑all patch, for example, caused by Gaeumannomyces graminis var. avenae is generally found only on creeping bentgrass varieties, and not on other turfgrass species. Similarly, summer patch disease caused by Magnaporthe poae is found on bluegrasses and fine fescues, but rarely, if ever, on perennial ryegrass varieties. Even within a turfgrass species, cultivars can vary in response to diseases. For example, varieties of Kentucky bluegrass such as Bristol, Eclipse, and Glade are relatively tolerant of summer patch disease, while varieties such as Chateau and Fylking are quite susceptible.

On golf courses where mixed stands of annual bluegrass and varieties of creeping bentgrass are quite common, it is frequently observed that the annual bluegrass is affected more severely, or shows symptoms much earlier, than the creeping bentgrass variety. This is sometimes true for root and crown diseases such as Pythium root rot caused by Pythium graminicola, anthracnose caused by Colletotrichum graminicola, and some nematode problems.

STEP 2. Observation of the Entire Affected Area for Symptoms

Where symptoms are located in the affected area, and how they appear, can reveal important information about the distribution of the disease and the types of pathogens usually found associated with that distribution pattern. For example, it is useful to know whether symptoms are restricted to wet, low lying areas, or to high, dry areas. It would also be noteworthy if symptoms were limited to areas of intense foot or equipment traffic, or to areas of extreme soil compaction. Equally important factors affecting symptom distribution are soil factors such as texture and pH as well as the degree of shade and the proximity of structures such as buildings, roads, and sidewalks that may alter soil temperatures.

The appearance of the symptoms is equally important. For example, it is important to note whether the symptoms appear randomly and without discernible structure throughout the affected area, or whether they are localized in patch‑ or ring‑like patterns. A number of turfgrass diseases usually appear as rings or patches, and only rarely diffused throughout susceptible turfgrasses. Root and crown diseases generally give rise to more patch– or ring–like symptoms; foliar diseases tend to result in more diffuse symptoms. In some cases, disease symptoms that appear patch‑like on close‑cut turf may seem diffuse on higher‑cut turf. On the other hand, foliar diseases such as dollar spot and red thread may actually appear patch‑like on both high‑cut and close‑cut turf.

Examining the overall complex of symptoms at this stage of the diagnostic process will help to sort out whether what is being observed is a biotic or abiotic problem. For example, if symptoms appear in a highly regular pattern, this may be indicative of a problem caused by maintenance equipment. For example, misapplication of fertilizers or pesticides, or the movement of equipment over heat‑stressed turf may appear in regular patterns. Examining turf at this stage may also reveal the presence of other noninfectious biotic factors such as insects, algae, or moss that may be contributing to the observed problem.

Often, when assessing overall symptoms, it is difficult to determine whether the problem under examination is currently active and worsening or has been inactive for some time. This is particularly true of diseases such as red thread, caused by Laetisaria fuciformis. On perennial ryegrasses and fine‑leafed fescues, necrotic patches from red thread damage are frequently apparent long after the pathogen has ceased to be active. Generally, the only way to tell this is to get down on one's hands and knees and examine turfgrass plants closely for the presence of progressive symptoms and/or the presence of pathogen structures. For foliar diseases, the mycelium or other structures are sometimes visible when the pathogen is active or has recently been active. For root diseases, fungal activity cannot be easily assessed.

STEP 3. Observation of the Specific Plant Symptoms

Specific symptoms on individual plants generally provide much more information on the possible cause of disease problems, and can be one of the most important diagnostic features available for some diseases. The principal above‑ground symptoms to look for at this stage are leaf spots, paying particular attention to the appearance of the lesions. For example, it's important to determine whether the lesions are irregular in shape or circular, whether they are bordered with a yellow (i.e. chlorotic) halo or by a purplish or brownish area. Blighting is another frequently observed above‑ground symptom in which the plant, particularly the leaves, turns brown (i.e. necrotic). With leaves, for example, it is important to note whether they appear to be blighting from the tip down, or from the basal stem upward. Other commonly‑observed above‑ground symptoms include wilting, stunting, and rotting. More specific observations about these symptoms would include such things as whether, during wilting or rotting, the plants appear to be dry, or are wet and greasy in appearance.

In addition to the appearance of specific plant symptoms, it is important to note the individual plant parts affected. Blighting symptoms may appear on leaves or sheaths, for example. Rots may appear on sheaths, roots, and rhizomes. Rotting symptoms are most frequently observed on below‑ground plant parts.

Root and Crown Diseases Present Special Problems

Root and crown diseases are challenging diagnostic problems. These challenges arise from a number of factors. One of the greatest obstacles to the accurate diagnosis of root and crown diseases is the perennial nature of turfgrass plants. Roots of nearly all mature turfgrass plants are continuously infected with many, if not all, of the pathogens capable of causing disease on a particular turfgrass species. As a result, microscopic examination of roots and crowns usually fails to identify a single pathogen as the cause of an affliction.

Another complicating factor is the presence of a large number of saprophytic fungi, which prefer to live on dead and decaying organic matter. Few of these fungi cause infection or disease in turfgrass plants, but they are readily observed on and in roots, rhizomes, stolons, and crowns. Some of them may even penetrate the roots of some turfgrasses, but they rarely, if ever, cause direct plant damage.

The natural senescence of many turfgrass roots also presents diagnostic challenges. Roots of turfgrasses naturally age and wither at a rapid rate. In the process, they are often colonized by a vast array of microorganisms, both pathogenic and non‑pathogenic. Since many of the pathogens causing root and crown problems prefer to live in a saprophytic mode, it is often not clear, when examining roots microscopically, whether a pathogen found to be present in the root was the cause of its decline, or colonized the root tissues after that decline had already set in. This dilemma is further complicated by the fact that, when examining roots microscopically, one can never be certain if the roots showing symptoms are the current year's or from the previous season, and if the previous year's roots, whether their decline was natural or disease‑induced.

One of the more aggravating problems in diagnosing root diseases is the difficulty in completing Koch's postulates satisfactorily. For the most part, the ability of root‑infecting pathogens to cause significant levels of disease depends heavily on environmental conditions and plant stresses. Turfgrass plants that are not under significant stress often fail to show foliar or root disease symptoms after infection of their roots. However, plants that are heavily stressed by excessively low mowing heights, excessively low or high fertilization regimes, excessively low or high soil moisture, excessive temperatures, high traffic, soil compaction, and certain pesticide applications are more likely to decline as a result of root infection. In addition, those pathogens infecting root tips, root hairs, or the epidermal layers of the root may not cause any significant necrosis, but may debilitate nutrient and water uptake through the root system. These types of pathogens may be particularly difficult to isolate from turfgrass roots, making it impossible to link them to the observed disease.

A critical aspect of the diagnosis of root diseases is the proper sampling and recovery of the root system from soil, so that thorough examination will be possible. Roots are typically covered with soil and other organic debris. They may also be difficult to free from thatch. All of these factors make root observations difficult.

When turfgrass managers examine the root systems of plants, a clump of turf is frequently ripped from the ground, teased apart to some degree, and examined in a way that can create artifacts. First, when roots are infected with pathogens, the root tissues often become fragile and easily subject to breakage. By ripping up a clump of turf, many of the diseased turfgrass roots are left behind in the soil, leaving healthy roots attached to the shoots. With just a casual inspection of such a sample, one might conclude that the roots were healthy, when in fact they might be seriously diseased. Second, soil and thatch in the specimen can make suitable observations of roots nearly impossible. A more effective method of removing roots from soil is to cut a section of affected sod with a knife to a depth of approximately 2 inches, then place the turfgrass specimen under a stream of water while gently pulling the specimen apart. The goal of this manipulation is to tease out individual plants with root systems intact and free of interfering thatch and soil debris. If special care is taken at this stage, an accurate diagnoses will be possible.

Just to complicate matters, it should be noted that numerous abiotic factors also contribute to root dysfunction and decline. Of particular importance here are high concentrations of soluble salts, root zone oxygen depletion, and excessive soil temperatures. The natural senescence of turfgrass roots, particularly during the summer months, further complicates the picture. These factors must always be taken into account when contemplating, or conducting, root disease diagnosis, and examined critically as part of any routine diagnostic procedure.

STEP 4. Field Observations of Pathogen Structures in Turfgrass Tissues

Since most fungi are identifiable by their characteristic reproductive structures, one of the more definitive pieces of evidence linking a specific pathogen to the cause of a disease problem is the presence of such structures. These are observed best in the laboratory, but they can be seen frequently on infected tissues in the field. The use of a 10X hand lens or other magnification device is a requisite for the identification of pathogen structures in the field. A good example of a disease for which diagnostic reproductive structures may be seen under low magnification is anthracnose, caused by Colletotrichum gramincola.

During disease development some pathogens produce structures that do not require magnification in order to be seen. For example, Laetisaria fuciformis, the cause of red thread, produces characteristic pink to red thread‑like structures which are readily visible and diagnostic. The same is true of pathogens such as Typhula incarnata, the cause of Typhula blight, and Erisyphe graminis, the cause of powdery mildew. Without a doubt, the observation and identification of pathogen structures associated with turfgrass plants can advance the diagnostic process significantly, since this information not only allows the identification of the pathogen, but, as they tend to be short‑lived, the presence of reproductive structures is an indication that the pathogen is or has recently been active.

Observation of Root Systems

Once individual plants are obtained with an intact root system, it is relatively easy to determine whether their roots show any disease symptoms. It may be useful to examine roots of apparently healthy turfgrass plants for comparison. Things to look for (and record) are:

1. The absence of root hairs.

2. Discolorations of the root system, particularly at the root tips.

3. Any noticeable lesions or other deformities and their specific appearance.

4. The condition of the crown area.

5. Whether discolorations or rotting appear to be progressing from the crown to the roots or from the roots to the crown.

6. Any visible fungal structures on or in the root and crown area (this usually requires a 10X or better hand lens).

7. The nature of the rotting on the root system. For example, do the roots exhibit a wet, gooey rot or a dry rot? The former is more characteristic of pathogens such as Pythium species while the latter is more representative of other patch disease root pathogens such as Magnaporthe and Leptosphaeria.

8. The presence of dark fungal mycelium growing on the surfaces of root and crown tissues.

These structures are often observable with a 10X hand lens or a dissecting microscope and are indicative of problems associated with patch diseases.

STEP 5. Recording the Cultural and Environmental Conditions

Recording the cultural conditions prior to and during the onset of disease symptoms is an important part of the evidence‑gathering process, and can be critical in making an accurate diagnosis. The same is true of the environmental and climatological conditions immediately preceding the onset of symptoms, which can quickly eliminate certain possible pathogens from consideration as potential causal agents.

Some of the important cultural conditions to record include: the age of the turfgrass planting, the specific fertilization, irrigation, and pest control practices employed, including materials and amounts applied. Grooming or growth management practices should be noted as well; so should any peculiarities such as increased traffic, excessive thatch, unusual soil odors, and the like. If appropriate, unusual features of the landscape such as the presence of large trees or roots in and around the affected site, shading, air and water drainage, and soil pH should also be noted.

The important climatological information to record would include maximum and minimum daily temperatures, relative humidity, rainfall, cloud cover and wind speed. Obviously, the most appropriate weather data would be those collected on the affected site. National Weather Service data may also be useful, however, if a recording station is located sufficiently near the site.

STEP 6. Attempting an Initial Diagnosis

At this stage, once all the pertinent field information has been gathered, a tentative diagnosis may be attempted. Numerous diagnostic guides have been written to aid in the diagnosis of turfgrass diseases. Disease identification manuals may be available from the state's land grant universities. Similar manuals may be available from pesticide and fertilizer manufacturers, the federal government, private consultants, professional turfgrass associations, and scientific societies. There are, in addition, number of textbooks devoted exclusively to turfgrass diseases. If no clear diagnosis can be made after making the observations, examining the cultural and environmental data, and consulting the manuals, then the next step in the process is to enlist the help of a competent laboratory diagnostician.

Root Diseases Should be Left to a Clinical Diagnostician

In nearly all cases, definitive diagnosis of root diseases requires a microscopic examination. This is necessary to actually observe the presence of the pathogen in infected and rotting roots and crowns. To accomplish this, small sections of symptomatic root, crown, rhizome, or stolon tissue are placed on a microscope slide and stained with chemicals designed to color the pathogen and not the plant tissues. In some cases, diagnosticians may use other chemicals to remove the contents of root cells, making observations of fungal structures in root tissues easier.

Occasionally, obvious pathogen structures are not apparent. In these cases, the laboratory diagnostician may attempt to isolate and culture the pathogens from root or crown tissues. This is usually accomplished by placing pieces of fresh root tissues on sterile synthetic culture media that foster the growth of microorganisms. Sometimes, if a specific group of pathogens is suspected, turfgrass roots may be placed on media containing chemicals that will only allow that group of organisms to grow. If pathogens are present, they will usually emerge from the infected roots and grow on the culture medium, facilitating a more detailed study of the organism. Once potential pathogens are recovered from infected roots, attempts can be made to complete Koch's postulates.

Most of the techniques used to diagnose root and crown diseases require specialized equipment and considerable expertise. Even experienced turfgrass pathologists have difficulties diagnosing some root and crown diseases on turfgrasses. As we learn more about the biology of root‑infecting turfgrass pathogens, however, and as more sophisticated techniques for their detection and identification are developed, root disease diagnosis will become more accurate.

STEP 7. Collecting and Submitting Samples for Clinical Diagnosis

In order to insure that the laboratory diagnostician has all the information required to make an accurate diagnosis, it is important that a proper sample be collected and that it be sent along with the appropriate field observations. Turfgrass samples with apparent above‑ground or below‑ground symptoms should be collected as the problem appears to be on the increase, preferably during the early stages of disease onset. Samples collected long after the problem was first observed are usually difficult to diagnose accurately. The samples collected should be representative of the symptoms observed over the entire affected area. Since the clinical diagnostician does not have the luxury of observing the problem first hand in the field, it is critical that the sample is accompanied by an adequate description of the problem, a record of the cultural practices, and a description of the environmental and climatological conditions that were present at the time the problem was first observed.

Critical information to include with the sample would be the following:

1. The grass species. If known, the precise cultivars.

2. A description of the overall symptoms, the date they first appeared, and the extent of the affected area. Be specific about symptom location and appearance.

3. A description of the cultural conditions prior to and during the onset of symptoms.

4. A description of the climatological conditions prior to and during the onset of symptoms.

5. A digital photograph of the affected area.

To facilitate comparison in the laboratory, it is ideal to collect a sample from apparently healthy turf as well as from the turf showing symptoms. However, samples should not be collected shortly after a fungicide application is made. Generally, if the fungicide is effective against the suspected pathogen, it will have done its work prior to the sample being analyzed, making it impossible to obtain a meaningful diagnosis.

If symptoms are patch‑like, sample from the edge of the patch, being sure to obtain both healthy and diseased turf in the sample. This allows the diagnostician to watch the disease progress in the laboratory. If symptoms are diffuse, take two samples: one from the diseased area and one from an adjacent apparently healthy area. Even though many turfgrass pathogens are readily apparent in both healthy and diseased turf, having both helps eliminate some pathogens as the primary disease‑causing agents since the relative abundance of a causal agent may be greater in a diseased than in a healthy turfgrass specimen. Turf collected from golf courses may be sampled with a cup cutter and need only be removed to a depth of two to three inches. If you do not plan to sample with a cup cutter, use a knife and cut a 6" X 6" piece of sod no more than two inches deep. Be sure to sample from both symptomatic and apparently healthy areas as described above.

Proper packaging of the sample for shipment to a diagnostic laboratory is critical. If the sample is relatively moist, wrap it in newspaper or aluminum foil, and place it in a cardboard box for mailing. If the sample is dry, moisten it slightly, wrap, pack, and mail as described above. Avoid wrapping samples in plastic or placing in plastic bags since these materials retain moisture in the sample and encourage many different organisms to grow, possibly masking important symptoms. Avoid exposure to heat or direct sunlight.

If a nematode problem is suspected, it is best to sample from both healthy and symptomatic areas. The most appropriate times to obtain such samples are in the spring, about a month after the turf greens up, and in the autumn, when turf may be more symptomatic. Sampling patterns depend on the symptoms present and the size of the affected area. If the turf is exhibiting a gradual decline, samples should be taken randomly throughout the area (in a zig‑zag pattern, for example). A minimum of six subsamples should be taken from an area that is 1/2 acre (~21,000 sq. ft.) in size. If symptoms appear in patches, subsamples should be taken just inside the periphery of the patch. All samples should be taken to a depth of approximately four inches. Subsamples may be taken with a cup cutter, a 1‑inch soil sampling probe, or a trowel. Subsamples should be mixed together, placed in a plastic bag and shipped immediately. Avoid exposure to heat or direct sunlight. It is best NOT to moisten samples.

It is always best to collect and mail turfgrass samples early in the week, so they do not spend the weekend in a post office or at the diagnostic laboratory. It is always helpful to telephone the diagnostic lab before sending the sample to make sure that the diagnostician is prepared to receive and process the sample quickly. This is particularly important during the busiest months of the season (June, July, and August). Whenever possible, samples should be sent to the diagnostic laboratory using an overnight delivery service.

STEP 8. Laboratory Examination of Turfgrass Samples

The close examination of turfgrass samples, whether in the field or in the laboratory, is a critical part of nearly all disease diagnoses. First, it serves as a means of verifying initial diagnoses based on field observations, and provides the turfgrass manager with a means of relating known causal agents and diseases to specific above‑ ground symptoms. Second, in the case of some diseases, it provides the only means of definitively identifying the cause of the problem. The purpose of this close laboratory examination is to find physical evidence for the presence of the causal agent(s). Nearly all fungi causing diseases in turfgrasses produce characteristic structures, reproductive as well as non-reproductive, in affected plants. Since nearly all of the fungal structures are microscopic, and therefore not visible without magnification, the clinical diagnostician depends heavily on the use of the microscope for these important observations. Generally, two types of microscopes are used in the examination of turfgrass specimens: a dissecting microscope for examining whole plants and plant organs, and a compound microscope for observing tissues and cells. Observation and classification of the fungal reproductive structures allows the diagnostician to more accurately identify the active pathogens. The structures for which diagnosticians look include: characteristic spore shapes, sizes, and colors, unique mycelial shapes and structures, sclerotia, and fruiting bodies such as pycnidia, acervuli, and perithecia. The diagnostician must also check for the presence of other causal agents such as bacteria, viruses, algae, and nematodes.

In some cases, no fungal structures may be apparent when tissues are observed under the microscope. In this case, leaf, sheath, or crown tissues may be incubated in a high‑humidity chamber to encourage whatever fungal pathogens may be present to grow in a mycelial form or to sporulate, thus revealing its reproductive structures for identification. These fungal tissues may then be transferred to laboratory culture media for further observation, or examined under the compound microscope. However, since many different microbes on or in affected turfgrass tissues can grow and reproduce in this environment, the diagnostician may find evidence of several different fungal pathogens, along with a myriad of nonpathogenic or saprophytic fungi and other microorganisms.

If physical evidence of a pathogen cannot be found in turfgrass tissue, other methods for the detection and identification of pathogens may be used. The most common back‑up method for pathogen detection and visualization is the isolation of the potential pathogen from the turfgrass tissue. Most fungal turfgrass pathogens can be readily grown on laboratory culture media. However, a few turfgrass pathogens are obligate parasites and are consequently not readily culturable. The latter include Puccinia and Uromyces spp., causing rust diseases, Erisyphe graminis causing powdery mildew, and Sclerophthora macrospora causing yellow tuft disease. Once a pathogen has been cultured successfully in the laboratory, its growth and reproductive habits can be observed more closely and its physical appearance compared with what was observed in the diseased tissue.

Over the past few years, even more sophisticated methods of pathogen detection have been developed. These include immunological techniques using pathogen‑specific antibodies to detect the present of specific pathogens in turfgrass tissues. More recent developments include methods for the analysis of pathogen DNA in the host tissue. These are similar to the blood DNA analysis currently used in courtroom murder trials. Such techniques provide some of the most sensitive and accurate methods available for identifying particular pathogens, and may prove to be the only means of confirming that the suspected pathogen is, in fact, the primary disease‑causing agent.

In the event no evidence of fungal pathogens can be found, the obvious conclusion is that the problem is either not a result of disease, or, if it is a disease, it can only be the product of a nonfungal pathogen. Other likely causal agents include viruses, bacteria, and nematodes. The problem could also be caused by noninfectious biotic agents such as algae, mosses, insects, or rodents, or by abiotic agents.

STEP 9. Making the Final Diagnosis: Pulling it all Together

Once all the pertinent information from field and laboratory has been assembled, the clinician faces the difficult task of interpreting all of the evidence and coming up with an accurate diagnosis. It should be noted that, while the process of assembling diagnostic evidence is rigorous, interpreting that evidence and making the diagnosis is more art than science. Making the actual diagnosis constitutes the greatest part of the educated guessing that goes on in this process.

Sometimes the evidence accumulated is either incomplete or inconclusive. In this case, further field observations, followed by another round of clinical examinations, may be warranted. In most cases, however, a diagnosis will prove possible.

Particularly in difficult cases, the results of the laboratory examination of the sample will be the pivotal evidence on which the diagnosis is b

Pest Management Guidelines A Cornell Cooperative Extension Publication	Cornell Guide for Pest Management of Turfgrass
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