6/6/2024 - By Harrell's

Summer is like flu season for lawns, with the increase in heat, moisture levels, and changing frequency of maintenance, your lawns are more susceptible to disease than normal. Read on to learn more about common diseases, what to look for to identify them, and how you can treat them with the proper prevention.

Foliar Lawn Disease - Dollar spot

Dollar spot is a fungal disease that blights leaf tissues but does not affect turf grass roots or crowns. Homeowners and lawncare professionals alike battle dollar spot throughout the growing season. This is truly one of the most common turf diseases that can affect numerous warm and cool season hosts across a wide range of temperatures and geographic conditions. Dollar spot prefers humid conditions and plenty of surface moisture from rainfall, irrigation, or dew but it will often be more severe in areas with low soil moisture. This means adequate irrigation and sufficient soil moisture and fertility can play a key role in combatting dollar spot severity.

Luckily, you have many fungicide options to control dollar spot - namely the DMI and SDHI classes of chemistry along with contact fungicides. Although dollar spot can be addressed in a more curative fashion, it is always best to apply fungicides preventively upon early detection or when conditions are conducive for disease, but before seeing symptoms. One protective product you may want to consider is Propiconazole, which offers broad spectrum and systemic disease control.

Foliar Lawn Disease - Brown Patch

Brown patch will manifest as sunken, circular patches of light brown colored grass depending on your mowing height. There may still be some healthy green grass sprouting up throughout the patches. Tall fescue lawns are most susceptible to brown patch, which is the primary disease issue throughout the summer months. Brown patch can also affect numerous other turf species at any mowing height, including intensively maintained lawns. Like dollar spot (and most other foliar diseases of turf), brown patch thrives in humid, cloudy, rainy conditions – although it tends to be most severe when temperatures are warmer and consistently in the 80s F.

Once thought to be a “nitrogen-loving” disease, recent research and evidence continue to point to brown patch being the most severe in turfgrass that is growing slowly through the summer months. Judicious, but strategic nitrogen fertility can help manage brown patch severity and help grow through minor infections. Another cultural strategy is related to limiting the amount of time the turf surface stays wet. This is accomplished by improving air movement or timing irrigation in the early morning hours. Fungicides in the QoI or strobilurin class of chemistry (i.e. Azoxy, Fluoxastrobin SC, Pyraclostrobin) are highly effective at managing brown patch both preventively and creatively.

Foliar Lawn Disease - Gray Leaf Spot

Gray leaf spot is another fungal disease that often forms during the rainy season, making summer a breeding ground for this disease in many areas. Gray leaf spot slows lawn grow-ins, thins out established stands, and can kill large areas of grass throughout a lawn. A prolific spore-producing fungal organism causes gray leaf spot to be a very problematic disease for lawns in the central and southern U.S. in the mid-to-late summer months. Spores can travel northward via jet streams and major storm systems, spreading spores as far north as New England and the upper mid-west. Gray leaf spot infects and spreads quickly, primarily on perennial ryegrass, tall fescue, and St. Augustine grass species.

The symptoms can often be confused with Pythium blight due to the rapid onset of symptoms and potential “tracking” or spreading of the disease with equipment and surface water movement. Lawns are particularly susceptible to gray leaf spot. Although it is sometimes difficult to treat preventively, treatment should be considered when temperatures are consistently above 80 F and rainfall and humidity remain on the high side leading into July. The top chemistries for gray leaf spot control include DMIs (Propiconazole), and T-Methyl.

Soilborne Lawn Disease - Summer Patch

Summer patch can be identified by small, circular patches of thinned-out and wilted lawns as they begin to manifest. As the disease persists, the patches begin to grow larger. Like other root-infecting fungi, summer patch ramps up on grass root systems during the spring and early summer. Because the pathogen compromises the plant’s ability to take up water and nutrients, even a little summer patch can be highly detrimental to the health of the turf, especially under summer stress. Once soil temperatures are consistently above 65° F, consider targeted fungicide applications to help protect turf roots.

On high-value lawns, bi-weekly or monthly applications of DMI’s, QoI’s, or combination products watered-in to the root zone are important to keep the roots clean and functional. Effective products include Azoxy, Fluoxastrobin SC, and Propiconazole. A dedicated focus on root health and growth is also key in helping the plant to grow through underlying levels of pathogen infection which tend to be abundant in most turfgrass systems. Root health product recommendations include Fleet® 100, EarthMAX® Organic, Root Enhancer, Seaweed A+E, and Mycorrhizae Pro.

Soilborne Lawn Disease - Fairy Ring

What makes fairy ring different from other circular-forming lawn fungi, is that fairy ring does not directly cause disease in the plant – instead, it alters the soil environment around the turf causing unique symptoms. Fairy ring most often appears on lawns with prominent levels of organic matter – also known as thatch. Fairy ring initially appears on turf in patches, rings, or half circles that can range in size. Fairy ring fungi can thrive in soil temperatures that are consistently above 55° F and exhibit a wide range of favorable conditions for growth, as well as appearing in turf stands, ranging from warm season to cool season grasses.

Managing thatch, proper moisture management, especially with wetting agents, and mitigating turf stress such as malnutrition or drought can often help suppress fairy ring symptoms. Regarding chemical management, several classes of chemistry are effective against fairy ring including the DMIs QoI’s (strobilurin), and certain SDHI chemistries. Combination products using these classes of chemistry are also useful in many situations. We recommend Azoxy and Fluoxastrobin SC.

Your Harrell’s Rep is Your Guide to Summer Disease

The summer months can throw all kinds of “curveballs” at lawn health, but when it comes to the diseases mentioned above, we will need to remain vigilant with scouting, identification, and strategic prevention. Your Harrell's Rep can help with up-to-date information related to cultural, nutritional, and chemical recommendations that can help specifically target your primary issues of concern. Reach out to your local Harrell’s representative for solutions that suit your needs.

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