Lawn disease occurs when a pathogen, most often a fungus, attacks turfgrass stressed by environmental factors or poor maintenance practices. Fungal infections require a susceptible host, a pathogen, and a conducive environment to take hold. These infections quickly lead to widespread discoloration, thinning, and death of the grass if not addressed promptly. Timely action is necessary to halt the infection’s spread and prevent long-term damage.
Identifying Common Lawn Diseases
Identifying the specific disease is the first step, as different infections require tailored management strategies. Many turf diseases present as brown patches, but their specific characteristics offer clues for diagnosis. Brown Patch, caused by the fungus Rhizoctonia solani, thrives in hot, humid conditions, appearing as large, circular patches several feet wide. A grayish “smoke ring” may be visible around the patch’s outer edge in the early morning dew.
Dollar Spot creates much smaller, sunken, straw-colored spots, usually the size of a silver dollar, which can merge into larger irregular areas. This disease is often associated with low nitrogen fertility and extended periods of leaf wetness. Rust disease is distinct because it gives the grass blades a reddish-brown or orange color that feels dusty when rubbed, due to fungal spores. Rust typically develops in the late summer or fall when grass growth is slow due to low nitrogen or dry conditions.
Cultural Practices to Halt Disease Spread
Adjusting maintenance habits is a primary line of defense against existing and potential infections. Proper mowing involves never removing more than one-third of the grass blade at any single time, which prevents excessive stress and preserves food reserves. Keeping mower blades sharp is important, as dull blades tear the grass, creating open wounds for pathogens. If a disease is active, bagging and removing clippings is advisable to prevent fungal spores from spreading across the lawn.
Watering practices directly influence the environment for fungal growth, since leaf wetness is a major factor in disease proliferation. Lawns should be watered deeply and infrequently, aiming to moisten the top four to six inches of soil. The best time for irrigation is early morning, which allows the grass blades to dry completely before nightfall, minimizing the duration of leaf wetness. Avoiding excessive nitrogen, especially during hot, humid periods, is another management strategy, as a flush of lush growth can increase susceptibility to diseases like Brown Patch.
Managing the soil environment through aeration and dethatching also reduces disease risk. Aerating the soil reduces compaction, which improves root growth and increases oxygen levels, a condition that pathogenic fungi generally dislike. Similarly, controlling the thatch layer—the tightly interwoven layer of living and dead organic matter—prevents moisture retention near the crown of the plant, which helps deny the fungi a favorable habitat. These non-chemical adjustments promote a healthier turf density that is naturally more resistant to infection.
Applying Fungicides for Active Infections
Chemical intervention with fungicides becomes necessary when cultural practices are insufficient to stop a severe or rapidly advancing infection. Fungicides are broadly categorized into two types: contact and systemic. Contact fungicides remain on the surface of the grass blade, forming a protective barrier that prevents new fungal spores from infecting the plant. They offer immediate control but are temporary and can be washed away by irrigation or rain, requiring reapplication.
Systemic fungicides are absorbed by the turfgrass and move within the plant’s tissues, providing longer-lasting protection and the ability to stop existing infections that have already penetrated the plant. While some systemic products offer curative action, they carry a higher risk of the fungus developing resistance if they are overused. To combat this resistance, it is important to rotate the fungicides used, alternating between different chemical classes, or modes of action.
Application requires careful attention to detail, beginning with accurately measuring the lawn area to ensure the correct dosage, as applying too little may be ineffective, while too much can harm the grass. Always read the product label for specific instructions on application volume, safety gear, and whether to irrigate immediately after application. For controlling foliar diseases, a lower volume of carrier water is typically used to ensure the product remains on the leaf surface, and it should be applied when the grass is dry. Fungicides can be used preventatively during high-risk seasons or curatively once symptoms appear.
Restoring the Lawn Post-Treatment
Once the active infection is controlled, the focus shifts to helping the lawn recover and fill in damaged areas. Recovery depends on the grass type; bunch-type grasses like tall fescue will require reseeding to cover dead patches. Grass species with runners, such as Kentucky bluegrass or Bermuda grass, will naturally spread to fill in surrounding dead spots. For completely dead areas, light topdressing with compost or topsoil prepares the surface for overseeding with a disease-resistant cultivar.
Overseeding should be done during the grass’s ideal planting season, typically fall for cool-season grasses and spring for warm-season grasses. The seeded area must be kept consistently damp until the new seedlings germinate. Resume fertilization gradually, applying a light feeding at about half the normal rate to encourage regrowth without causing weak, susceptible tissue. Maintaining improved cultural practices is necessary to ensure the long-term health of the turf and prevent future outbreaks.