Disease Control

Lawn disease is one of the serious and costly reasons for injury and death to grasses used in lawns, golf courses, sport fields, and other areas where grasses are desired. An accurate diagnosis of the problem is essential to any successful control program. Disease identification and control involve more than just waiting for diseases to appear, then trying to make a rapid diagnosis and applying a fungicide. Most disease identification guides show only the symptoms of developed diseases. This is helpful, but it is more important to know the conditions that can lead to a disease, and to follow basic cultural practices that can reduce your potential for a disease. Knowing when and under what conditions to anticipate various Lawn diseases, an individual can prepare for what to do about them, saving time and achieving better results in disease control. 

Key Points for Maintaining Healthy Lawns

  • Select an appropriate Lawn species for the location. Consider:
    - climate,
    - shade (light and air circulation),
    - soil type and conditions,
    - terrain,
    - susceptibility to pests, and
    - use of the turf area.
  • Prepare the site before planting:
    - Remove debris.
    - Grade the area.
    - Provide good drainage.
    - Take a soil test and amend soil as needed.
    - Eliminate weeds.
  • Avoid watering late in the day or at night.
  • Apply enough water in each application to completely wet the root zone.
  • Apply the appropriate amount of water based on species, soil, and climate.
  • Provide adequate light penetration and air circulation.
  • Apply the appropriate amount of fertilizer (based on a soil test).
  • Mow frequently, maintaining the tallest height recommended for the species.
  • Be sure to use mowers with sharp blades.
  • Leave clippings on the lawn surface.
  • Dethatch by aerating, raking, or vertical mowing as needed.

Managing Lawn diseases

Environmental conditions strongly influence disease occurrence. Although many of the causal agents are always present in turf, diseases do not occur until conditions are favorable for pathogen development. For example, brown patch disease requires wet, humid conditions during warm to hot weather. Being aware of the conditions that increase disease potential is important in taking preventive measures such as applying fungicides before symptoms appear. But before fungicides are considered, there are several Lawn management practices that need discussion in hopes of reducing the potential for disease. Refer to Table 1 for host species, disease symptoms, conditions favorable for infection and recommended cultural practices and fungicide treatments.

Soil fertility

Soil fertility is an important factor in disease development. High nitrogen levels increase the susceptibility of cool-season grasses (Kentucky bluegrass, tall fescue, perennial ryegrass, fine fescue and bentgrass) to leaf spot, Rhizoctonia brown patch and Pythium blight. Low nitrogen levels increase Lawn susceptibility to dollar spot and red thread. Low potassium levels in the soil reduce Lawn tolerance to high temperatures and drought stress, which can increase the potential of diseases such as summer patch. Low pH is often associated with diseases such as brown patch as well.

Knowledge of soil fertility as it relates to Lawn diseases can help guide an individual in deciding how to manage a lawn. A tall fescue lawn can receive two or three fertilizer applications throughout the fall and perhaps receive no additional fertilizer in the spring to reduce the potential for brown patch. Like tall fescue, Kentucky bluegrass can receive fall fertilization but can also receive fertilizer in the spring to help keep dollar spot from infecting the bluegrass.

To minimize the potential for disease, supply enough nitrogen that proper mowing is required on a weekly basis. Sometimes a light application of nitrogen will produce enough active leaf growth that disease symptoms are no longer visible.

Mowing

Lawn plants mowed shorter than their optimal height of cut are, in general, more susceptible to diseases. Optimal cutting heights for cool-season grasses range from 2.5 to 4.0 inches, depending on the species. Warm-season grasses can range between 1 and 2 inches.

Seasonal variation in mowing height was once thought to be highly beneficial and is still considered beneficial by some. We know that mowing cool-season grasses a little taller in the summer months can have benefits through summer stress periods (deeper roots, better cooling effect). We also know that cool-season grasses mowed a little taller in the spring and fall compete more successfully against weeds. Therefore, select the tallest, acceptable mowing height for your species of grass and maintain that height during the entire season. This provides benefits throughout the season — competition against weeds as well as reduced summer stress.

Frequency of cut should be determined by the "one-third rule" of mowing. You should make sure that no more than one-third of the leaf growth is removed 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 mower blade inflicts more and bigger wounds that increase potential for infection by Lawn diseases.

Observe leaf tips or grass clippings collected on your mower deck immediately after a mowing to determine the quality of cut. Use this as an indicator of when to sharpen blades.

Thatch control

Essentially all Lawn diseases are 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 excellent habitat for active and dormant stages of disease-causing organisms. When environmental conditions are optimum, fungi can rapidly grow and infect living turf tissue.

Remove excess thatch when turf is actively growing to promote quicker recovery from power-raking or verticutting. Remove thatch in the spring before application of crabgrass preventer, or in the fall for cool-season grasses and midsummer for warm-season grasses.

Core aerification (removing soil plugs) is a slower process of thatch control but will cause less direct stress on the turf. Breaking up soil plugs and filtering soil into the turf canopy allows soil microbes to breakdown dead organic matter in the thatch layer.

Remove excess thatch when it accumulates to a half inch or more in taller-mowed turf (1.5 to 4 inches) and one-quarter inch in lower-mowed turf (less than 1.5 inches).

Soil aeration and drainage

A good exchange of air between the soil and atmosphere is necessary for vigorous Lawn growth. Turf areas that stay constantly wet because of poor soil conditions are prime targets for water-favoring, soil-borne diseases such as Pythium blight and brown patch. Surface contouring and subsurface drainage can be costly but permanent solutions to wet soils.

Core aerification and slicing are turf management practices that can be repeated during the season to temporarily increase air exchange and soil drying.

You can also increase light penetration and air movement by selectively pruning your trees and shrubs. This will speed the drying of poorly drained areas and also reduce the humidity in localized turf areas.