IPM Identification and Mangement Of Turfgrass Diseases
The Plant Disease Triangle
Establishment and maintenance of turfgrasses is a multibillion dollar industry in the United States for good reason. Turfgrasses don’t just add beauty to one’s surroundings. Natural grasses provide safe and attractive playing surfaces for sports and other leisure activities. Vigorous, well-rooted turfgrass stands also protect local watersheds by filtering out harmful substances and reducing soil erosion and runoff. Turfgrasses cool the immediate environment in the heat of the summer and purify the air by removing carbon dioxide and releasing oxygen.
Millions of dollars are spent annually in the United States on fungicides to prevent or arrest turfgrass disease development on golf courses, high-maintenance lawns and other landscapes. Additional money is spent to repair and renovate severely damaged turf. Accurate diagnosis is the key to managing turfgrass disease in an economically and environmentally sound manner.
There are two types of pathogens that cause plant disease: (1) infectious or biotic and (2) noninfectious or abiotic. Most of the common infectious turfgrass diseases are caused by plant pathogenic fungi. The symptoms of these fungal diseases and factors favoring pathogen development have been well described. With some background information, the identification of fungal diseases is a straightforward process.
Cultural practices such as mowing, aerification and irrigation or the misuse of herbicides, growth regulators, fungicides and fertilizers can cause turfgrass injury or decline. These abiotic plant diseases are often the most difficult to diagnose. Disease may also result from a complex of organisms in combination with environmental factors that reduce host plant vigor.
This publication is designed to be a useful reference for diagnosticians, turfgrass managers, industry representatives and others who want to learn how to diagnose and manage common turfgrass diseases caused by plant pathogenic fungi. Expert help in turfgrass disease diagnosis can be obtained from Plant Diagnostic Clinics at land grant universities or from the private diagnostic labs specializing in turfgrass disease diagnostics.
The plant disease triangle, which illustrates how disease develops in a plant population, is a useful concept to help understand and manage turfgrass diseases. For turfgrass disease to occur, the following three components must all be present:
• The pathogen: the disease-causing agent (biotic or abiotic)
• The environment: environmental conditions, such as temperature and moisture that favor pathogen development or reduce host vigor.
Identifying the grass species involved is an important clue for identifying the probable cause. Some diseases occur more commonly on one species than another. After you have identified the turfgrass species showing symptoms, refer to Table 1 for a list of the most common turfgrasss hosts for the diseases covered in this publication. Cross reference to Table 2 to check the prevailing temperature and time of year. The section on Tips for Diagnosing Turfgrass Disease can also help with the diagnosis.
Potential turfgrass pathogens are present wherever turfgrass is grown. But manipulating the other two components of the disease triangle can often provide effective disease management. Before applying fungicides, consider modifying the host, modifying the environment, or both. These considerations can be combined in a cultural disease management program that includes decisions related to selection of adapted and resistant turfgrass species and cultivars, fertility, mowing, water management, thatch removal and core cultivation.
The information herein is supplied with the understanding that no discrimination is intended and that listing of commercial products, necessary to this guide, implies no endorsement by the authors or the Extension Services of Nebraska, Colorado, Wyoming or Montana. Criticism of products or equipment not listed is neither implied nor intended. Due to constantly changing labels, laws and regulations, the Extension Services can assume no liability for the suggested use of chemicals contained herein. Pesticides must be applied legally complying with all label directions and precautions on the pesticide container and any supplemental labeling and rules of state and federal pesticide regulatory agencies. State rules and regulations and special pesticide use allowances may vary from state to state: contact your State Department of Agriculture for the rules, regulations and allowances applicable in your state and locality.
