UACES Facebook Half-healthy, half-sick––taking a proper turf disease sample…
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Half-healthy, half-sick––taking a proper turf disease sample…

Wendell Hutchens

Turf pathologists and disease diagnosticians frequently inspect sick turf samples under the microscope to determine if potential pathogens are causing turf health to decline. These samples are commonly sent into diagnostic clinics from turf professionals, extension agents, and homeowners, alike. You must remember, diagnosticians only have the information you provide them with, and many pathogens are frequently present in any given sample that arrives in the diagnostic clinic even though they may not always be the cause of the symptoms you are seeing. The best example of this is the winterkill issues (Figure 1).

Turf with patches of dead grass

Naturally, the tendency is to think the death and destruction is from a disease, especially since plant pathogens can often be found in the dead and decaying turf samples. However, you must remember, just because we find pathogens in a sample does not mean the devastation is caused by that pathogen...the turf symptoms must match up with the pathogen(s) present. If you submit an improper turf sample, no supporting pictures, and no supporting spray records to the diagnostic lab, correct disease identification is extremely difficult.

Question…when you feel sick or in pain, do you go into the doctor’s office and sit silently expecting the doctor to figure out what is wrong with you without any communication whatsoever? No, you usually tell the doctor how you are feeling or where it hurts or when you started feeling bad or what medicines you have taken, etc. Withholding this information drastically slows down the diagnostic process. Just giving the doctor some basic information will greatly expedite the diagnosis. The same thing applies to diagnosing plant diseases (a special thanks to Dr. Jim Kerns for that analogy). If you have a turf area that you think is diseased, three things need to happen for you to get a quick and accurate diagnosis:

  • You must take a proper sample
  • You must overnight ship the sample to keep it viable
  • You must provide supporting pictures and any spray records you have on hand

1)  Taking a proper turf sample takes just a few simple steps. You must first identify an area that looks abnormal. Look for declining turf, patches, spots, leaf lesions, etc. (Figure 2) prior to taking a sample.

Left image shows patches, Right image shows lesions.

You then must take a cup-cutter if you have one or a hand shovel and remove a plug from the edge of the sick area. This sample needs to have half of the plug in the healthy area and half of the plug in the sick area (Figures 3 & 4).

Ideal sampling area in the field, half healthy, half sick.
Ideal sample in a petri dish, half healthy, half sick. Fungus has grown where the healthy half meets the sick half.

This interface between sick and healthy turf is where the pathogen (if there is one) is most active, thereby increasing the diagnostician’s chances of finding and identifying the pathogen under a microscope. For example, brown patch on tall fescue is easily identified microscopically as the pathogen R. solani produces right-angled hyphae (Figure 5).

Microsopic view of brown patch on tall fescue.

Another ABSOLUTELY CRITICAL thing to remember is to take the sample BEFORE spraying a fungicide. It is okay to spray a fungicide for a disease (that is what fungicides are for), but, if you want the disease identified, you must take a sample first because as soon as the fungicide is applied there is a high likelihood that the fungicide will suppress the pathogen tremendously. This makes finding the pathogen in a sample sent after a fungicide application nearly impossible.

2)  Overnight shipping the sick turf sample will help with a rapid and accurate diagnosis. Pathogens can be If turf samples are not kept in a cool and appropriate environment, they can die off or other saprophytic, non-pathogenic fungi can proliferate and overshadow the actual pathogen. After a sample is taken, wrap the plug in aluminum foil, place securely in a box, and overnight ship it to the diagnostic clinic (Figure 6).

Correct sample shows complely wrapped in foil, incorrect is partially wrapped.

3)  Providing supporting pictures and spray records along with the turf sample can make or break a proper diagnosis. The ideal way to take pictures of a diseased area is to take a picture starting with the area as a whole, then take a close-up picture of the diseased area, then take a picture of individual plants expressing symptoms (Figure 7a,b,c).

By doing this, you can capture the disease in the context of the surrounding area, get a closer image of the diseased area itself, and an even more close-up image of individual diseased plants. This allows the diagnostician to gain a better understanding of what the damaged area looks like and also allows them to see what the stand and plant symptoms look like. Also, taking photos that include a reference (e.g., a ruler, pocketknife, car keys, pencil, etc.) is important for the diagnostician to gauge the size of the area. Moreover, taking photos of the disease in proper lighting and when symptoms are clearly showing well helps the diagnostician make an accurate diagnosis. Lastly, if you have any recent spray and fertilizer records, including those along with the sample will help the diagnostician piece together what the problem is.

Three photos of a diseased area, showing the entire area, a close-up image, and individual plant.

If you follow the above guidelines for taking a proper turf disease sample, you will get a more rapid and accurate diagnosis.

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