IPM Identification and Mangement Of Turfgrass Diseases
Using Cultural Practices to Manage Disease
Selecting turfgrass species and cultivars. Choose turfgrass species and cultivars that are adapted to site conditions and local climate. The National Turfgrass Evaluation Program (NTEP) was organized to evaluate cultivar performance of turfgrasses over wide geographic areas of the United States. Information in the NTEP reports is a good source for identifying regional adaptation and relative disease resistance. Visit http://ntep.org to review these reports. MU publication G6772, Cool-Season Grass Cultivars for Athletic Fields, presents ratings for Kentucky bluegrass, tall fescue and perennial ryegrass. Although the focus of the publication is athletic fields, the listings can be helpful in selecting cultivars for home lawns as well. It is often difficult for individuals to find seed of recommended cultivars. A good approach is to list what local retailers have available and then cross-reference to the cultivars recommended for your location.
Some diseases can be completely avoided by selecting or substituting grass species that are not susceptible to certain pathogens. For example, the severity of summer patch in Kentucky bluegrass lawns or golf green surrounds can be reduced by overseeding with tall fescue.
Fertilizing. Healthy, vigorous turfgrass often withstands infectious disease and adverse environmental conditions. A fertility program that promotes turfgrass vigor is an important part of a sound disease management program. Although the specifics of any program must be left to the turfgrass manager because of the on-site differences in use, expectation and budget, there are several generalizations that can be made. Decisions on amount and type of nutrients to apply should be based on the level of available nutrients in the soil and the plant’s nutrient status as determined through soil testing and plant analysis.
For cool-season grasses, most of the nitrogen requirement should be met in the fall. Heavy spring applications of nitrogen result in lush, dense growth that is more disease prone. Growth of foliage at the expense of roots will also make the turfgrass more prone to decline situations during the heat and moisture stress periods frequently encountered in the summer.
For warm-season grasses, nitrogen requirements should be spaced out over the summer months (May-August) when these grasses are actively growing. Late-summer to early-fall applications of nitrogen will make these grasses more susceptible to cold/cool weather diseases.
Mowing. Turfgrass plants mowed shorter than their optimal height of cut are, in general, more susceptible to disease. Optimal cutting heights for cool-season grasses range from 2.5 to 4.0 inches, depending on the species. Height of cut for warm-season grasses can range between 1 and 2 inches.
Frequency of cut should be determined by the “one-third rule” of mowing. Do not remove more than one-third of the leaf growth during a single mowing.
Mowing creates wounds through which fungi can enter the plant and infect it. Leaf cuts made by a sharp mower blade are cleaner and heal faster than the tearing and shredding caused by a dull mower blade. A dull blade inflicts more and bigger wounds that not only increase the potential for infection by turfgrass pathogens but also increase the potential for moisture stress. Observe leaf tips or grass clippings collected on the mower deck immediately after a mowing to determine the quality of cut. Use this as an indicator of when to sharpen blades.
Although ambient temperature, relative humidity and amount of precipitation cannot be controlled, there are ways to modify the local environment to reduce the negative impact of turfgrass disease. Development of many turfgrass diseases is favored by extended periods of leaf wetness. Extended periods of leaf wetness in the turfgrass environment are caused by dew, guttation (water droplets that form at the tips of grass leaves) and frequent irrigation or precipitation. Remove dew and guttation from grass leaves by dragging a hose across the surface, using a whipping pole or briefly irrigating it with large droplets, only long enough to remove the dew from the leaf surface. The goal of all three methods is to spread the concentrated dew or guttation droplets over a larger surface area so the turf canopy will dry faster in the morning. Recent research results suggest that dew removal can improve the performance of certain contact fungicides.
Improper irrigation alone can create a disease problem that normally would not exist. Ideally, irrigation should be applied between midnight and early morning when the turfgrass canopy is normally wet. This avoids extending the duration of leaf wetness. Avoid frequent irrigation that also extends the duration of leaf wetness, especially when environmental conditions are favorable for Pythium foliar blight, brown patch and dollar spot. Generally, deep and infrequent irrigation is recommended so that some soil and leaf drying can occur, permitting a gaseous exchange between soil and atmospheric air.
Irrigation water should be tested regularly (every two to three years) for pH, soluble salt concentration, level of bicarbonates and other factors that influence irrigation water quality. Adequate drainage is necessary for vigorous turfgrass growth. Turf areas that stay constantly wet because of poor drainage are prime targets for decline. Surface contouring and subsurface drainage are costly, but permanent solutions. Core cultivation and slicing are turf management practices that can be repeated during the year to temporarily increase infiltration rates and promote soil drying.
Increase light penetration and air movement by selectively pruning trees and shrubs. This will speed the drying of poorly drained areas and also reduce the humidity in localized turfgrass areas.
The negative impact of turfgrass disease can be reduced by good thatch control. Thatch is a layer of dead and living plant material located between the soil surface and green turf canopy. It is an excellent habitat for both active and dormant stages of many plant pathogenic fungi. When environmental conditions are optimum, fungi can rapidly grow and infect living turfgrass tissue.
Remove excess thatch when it accumulates to ½ inch or more in taller-mowed turf (1.5 to 4 inches) and ¼ inch in lower-mowed turf (below 1.5 inches). Dethatch when the turfgrass is actively growing, so it will recover quickly. Generally dethatching should occur in the spring and fall for cool-season grasses and midsummer for warm-season grasses.
Core cultivation is another tool for thatch control. On sand-based or modified sand-based putting greens, cores are generally removed and the holes are backfilled with sand. On other turf areas, the cores can be broken up and filtered back into the turf canopy to promote the activity of soil microbes that break down organic matter in the thatch layer.
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.
