Summer is tough on turf. With increased heat, higher moisture levels, and changing maintenance routines, lawns become more susceptible to diseases. Of course, more diseased lawns means more customer unhappiness and more cancels. Identifying common lawn diseases, recognizing their symptoms, and learning how to treat and prevent them effectively will help you manage customer callbacks and complaints and keep your customers happier.

Lawn Disease Identification

We asked our partners at Harrell’s to tap into some of their wealth of agronomic knowledge to share with us. They’ve provided us with this guide which reviews some of the most notorious lawn diseases and provides preventive and curative solutions for control. But remember, not all products are registered in all states. Your Harrell’s rep (or vendor partner) is often one of the best resources for product recommendations and programs to combat lawn diseases before they start.

Foliar Lawn Disease – Dollar Spot

Dollar spot is a fungal disease that affects leaf tissues but not turf grass roots or crowns. Lawn care professionals encounter dollar spot throughout the growing season. It’s one of the most common turf diseases, affecting various warm and cool-season grasses across diverse climates. Dollar spot thrives in humid conditions with ample surface moisture from rainfall, irrigation, or dew, but it becomes more severe in areas with low soil moisture. Thus, adequate irrigation and sufficient soil moisture and fertility are crucial in mitigating dollar spot severity.

Fortunately, there are many fungicide options to control dollar spot, including DMI and SDHI classes of chemistry, along with contact fungicides. While dollar spot can be treated curatively, it’s best to apply fungicides preventively upon early detection or when conditions are conducive to the disease but before symptoms appear. A recommended product is Propiconazole, which offers broad-spectrum and systemic disease control.

Foliar Lawn Disease – Brown Patch

Brown patch appears as sunken, circular patches of light brown grass, depending on your mowing height. Some healthy green grass may still sprout within the patches. Tall fescue lawns are particularly susceptible to brown patch, a primary disease issue in the summer months. Brown patch also affects other turf species at any mowing height, including intensively maintained lawns. It thrives in humid, cloudy, rainy conditions and is most severe when temperatures are consistently in the 80s F.

Recent research suggests brown patch is the most severe in turfgrass that is growing slowly during the summer. Strategic nitrogen fertility can help manage brown patch severity and support recovery from minor infections. Limiting the turf surface’s wetness by improving air movement or timing irrigation in the early morning hours is also effective. Fungicides in the QoI or strobilurin class of chemistry (e.g., Azoxy, Fluoxastrobin SC, Pyraclostrobin) are highly effective for both preventive and curative management of brown patch.

Foliar Lawn Disease – Gray Leaf Spot

Gray leaf spot is a fungal disease that often emerges during the rainy season, making summer a prime time for its development. It slows lawn growth, thins out established grass, and can kill large areas of grass. This prolific spore-producing fungus is particularly problematic in the central and southern U.S. during mid-to-late summer. Spores can travel northward via jet streams and storm systems, spreading as far north as New England and the upper Midwest. Gray leaf spot spreads quickly, mainly affecting perennial ryegrass, tall fescue, and St. Augustine grass species.

Gray leaf spot symptoms can be confused with Pythium blight due to their rapid onset and potential spreading through equipment and surface water movement. Lawns are highly susceptible to gray leaf spot, and preventive treatment is challenging. However, consider treatment when temperatures are consistently above 80°F and humidity is high. Top chemistries for gray leaf spot control include DMIs (like Propiconazole) and T-methyl.

Soilborne Lawn Disease – Summer Patch

Summer patch appears as small, circular patches of thinned and wilted grass. As the disease progresses, these patches grow larger. Like other root-infecting fungi, summer patch impacts grass root systems during spring and early summer. The pathogen compromises the plant’s ability to absorb water and nutrients, making summer patch particularly detrimental under summer stress. When soil temperatures consistently exceed 65°F, targeted fungicide applications can help protect turf roots.

For high-value lawns, bi-weekly or monthly applications of DMI’s, QoI’s, or combination products watered into the root zone are essential to maintaining root health. Effective products include Azoxy, Fluoxastrobin SC, and Propiconazole. Focusing on root health and growth helps plants overcome underlying pathogen infections, which are common in most turfgrass systems. Recommended root health products include Fleet® 100, EarthMAX® Organic, Root Enhancer, Seaweed A+E, and Mycorrhizae Pro.

Soilborne Lawn Disease – Fairy Ring

Fairy ring differs from other circular-forming lawn fungi because it does not directly cause disease in the plant but alters the soil environment around the turf, causing unique symptoms. Fairy ring often appears on lawns with high organic matter, or thatch. It manifests as patches, rings, or half circles of varying sizes. Fairy ring fungi thrive in soil temperatures above 55°F and in diverse growing conditions, affecting both warm- and cool-season grasses.

Managing thatch, proper moisture management with wetting agents, and mitigating turf stress like malnutrition or drought can suppress fairy ring symptoms. Chemical management with several chemistry classes, including DMIs, QoI’s (strobilurin), and certain SDHI chemistries, is also effective. Combination products using these chemistries are useful in many situations. Recommended products include Azoxy and Fluoxastrobin SC.

Rely on Experts to Help You With Summer Lawn Disease Management

Summer can present numerous challenges to lawn health, but vigilance in scouting, identification, and strategic prevention can help manage diseases. Your Harrell’s representative can provide up-to-date information on cultural, nutritional, and chemical recommendations tailored to your specific concerns. Reach out to your local Harrell’s representative for customized solutions.

Note: Not all products are registered in all states. Always read and follow the instructions on the product label, as not all products are labeled for all purposes.