According to Andy Hamblin and Hank Wilkinson, associate professors in plant pathology, University of Illinois Turfgrass Program, Urbana, Ill., there are five steps lawn care operators should take to accurately diagnose turfgrass diseases.
1. Identify the turfgrass species
What species of grass is affected?
On what variety, if known, did symptoms appear?
Was a seed blend or mixture used?
Was the grass recently seeded or overseeded?
2. Observe the symptoms
Are patches circular or irregular? What is the diameter of the patch?
Do the leaves show general wilting or yellowing? Do the leaves have spots? Are the spots bordered with a colored margin? Do the spots originate from the leaf tip or within the leaf midsection? What color are the spots?
Are the crowns infected? Can the plant be easily pulled apart from the stem base? Is the crown blackened?
Are the roots discolored brown or black? Have the roots been pruned to stubbled ends?
3. Observe the environment
What was the temperature when symptoms first appeared? What is the current temperature?
Have heavy or persistent rains, excessive irrigation or drought conditions precluded symptom development?
Were pesticides or fertilizers recently applied?
Does thatch exceed ½-inch in symptomatic areas?
Is the damaged area shaded, or does it lack proper air circulation?
Did the symptoms occur in either a low area with standing water or on a knoll or ridge?
What is the pH and soil fertility of the symptomatic area?
What is the mowing height?
4). Observe signs of the pathogen
Are sterile hairs (mycelia) present on the leaf surface, especially early in the morning? If so, what color are the hairs?
Are small brown or black dots present on the surface of leaves, sheaths, crowns, or roots?
Within necrotic leaves, are dots present or are spores produced? What color are the spores, if present?
Are tan to black-hardened masses present on plants? If so, what is the size and shape?
5). Look up disease characteristics in the following references:
Compendium of Turfgrass Diseases, Second Edition
A Guide to Integrated Control of Turfgrass Diseases, Volumes I & II.
Controlling Turfgrass Pests, Second Edition
The author is Managing Editor of Lawn & Landscape magazine and can be reached at nwisniewski@lawnandlandscape.com.