Identifying & Preventing Brown Patch

Brown patch is the most common and well-known lawn disease in Nebraska and the rest of the country. Caused by the fungus Rhizoctonia solani, brown patch can spread rapidly under the right conditions, leaving dead-looking patches across your lawn. Understanding how to identify and deal with brown patch is essential for keeping your lawn healthy. So, join the Summit Lawns team as we go over the information you need to defend your turf against brown patch!

Identifying Brown Patch

The first step in tackling brown patch is recognizing the symptoms early. Brown patch typically appears as circular or irregularly shaped patches of dead or dying grass. These patches can range from just a few inches in diameter to several feet across, depending on the severity of the outbreak. In the early stages, the affected grass may look water-soaked or wilted, but as the disease progresses, it turns brown, tan, or yellowish in color.

Grass blades affected by brown patch often appear thin, withered, and may have lesions with irregular tan or brown spots. The fungus primarily attacks the leaf blades rather than the roots, so the grass may survive but look damaged and unhealthy. The patches can merge, creating large, unsightly areas of dead grass.

Many homeowners mistake brown patch for drought stress, dog urine damage, or grub infestations, but these issues tend to have different patterns. Unlike brown patch, drought stress affects grass more uniformly and does not have a distinct border or smoke ring. Identifying brown patch correctly is crucial because using the wrong treatment methods can worsen the problem rather than resolve it.

Key Identifiers

Circular, brown patches
Diameter between a few inches and 3 feet
Smaller patches blending together
Foliar lesions on grass blades
Mycelium spreading in morning
Gray smoke-ring perimeter

Causes Of Brown Patch

Brown patch thrives under specific environmental conditions, particularly during warm, humid weather. Brown patch is most prevalent in the summer and early fall when nighttime temperatures remain above 65°F and humidity levels are high. Temperatures consistently between 70°F and 90°F are the ideal breeding ground for the brown patch fungus to develop and spread. The fungus spreads rapidly when moisture stays on the grass blades for long periods, especially overnight.

Excess moisture is one of the biggest culprits behind brown patch. Lawns that are watered too frequently, particularly in the late afternoon or evening, create the perfect breeding ground for Rhizoctonia solani. Wet grass blades and soggy soil encourage fungal growth, allowing the disease to spread quickly. Poor drainage further exacerbates the issue by trapping moisture, making it even harder for grass to dry out properly.

Too much nitrogen can also make your grass more susceptible to brown patch. High nitrogen levels encourage fast, lush growth, but this new growth tends to be weak and vulnerable to fungal infections. Lawns that receive heavy nitrogen applications in the summer months are at a higher risk of brown patch outbreaks, especially in compacted soils. Thick thatch layers, compacted soil, and poor airflow around your lawn contribute to brown patch by trapping moisture and creating a humid environment where the fungus thrives.

Contributing Factors

Poor lawn drainage
Overwatering
Over-/under-fertilizing
Drought stress
Compacted soil
Mowing Too Low

Grass Types Affected By Brown Patch

Brown patch can affect almost any type of grass, but some varieties are more susceptible than others. The term “brown patch” exclusively refers to lawn disease in cool-season grasses cause by the Rhizoctonia solani. The same fungus infecting warm-season grass types is known as “large patch.” Though the same fungus is responsible for both diseases, these are considered to be two separate lawn diseases for the two different categories of grass types.

Cool-Season Grasses at Risk

Tall Fescue: One of the most commonly affected grasses, tall fescue can develop severe brown patch damage in hot, humid weather.
Perennial Ryegrass: Highly susceptible, especially in areas with poor drainage.
Kentucky Bluegrass: Less vulnerable than fescue and ryegrass but still at risk in warm, damp conditions.

Warm-Season Grasses at Risk (For Large Patch)

St. Augustinegrass: Particularly susceptible in humid climates like the southeastern U.S.
Bermudagrass: Can develop brown patch in mild fall and spring temperatures.
Zoysiagrass: More resistant than other warm-season grasses but still prone to infection in prolonged wet conditions.

Dangers Of Brown Patch In Your Lawn

One of the biggest concerns homeowners have about brown patch is whether it permanently kills grass. The good news is that brown patch typically does not kill the grass outright, as it primarily attacks the leaf blades rather than the roots. However, the disease can still cause significant damage and stress, weakening your lawn and making it more vulnerable to other problems.

In mild cases, the grass can recover on its own once conditions improve and proper lawn care practices are implemented. However, severe or repeated infections can lead to thinning, weak growth, and dead patches that struggle to bounce back. If the grass is already unhealthy due to poor soil, improper mowing, or lack of nutrients, brown patch can accelerate its decline. To prevent long-term damage, it's important to act quickly when brown patch appears. The sooner you address the issue, the better the chances of recovery.

How To Prevent Brown Patch

Preventing brown patch is much easier than trying to treat it once it has spread. There are certain steps you can take to greatly reduce the chances of brown patch developing in your grass or to help mitigate the damage if the disease does develop. If brown patch does appear, fungicides can be effective. Products containing azoxystrobin and propiconazole are ideal for treating Rhizoctonia solani, but they must be applied carefully to avoid further damage to your turf. To avoid the need for fungicide treatments, follow the steps listed below.

Water Wisely: Water early in the morning to allow the grass to dry before nightfall. Avoid frequent shallow watering—use deep, infrequent watering to encourage strong roots. Improve drainage in areas where water tends to pool.
Mow at the Right: Height Never cut more than ⅓ of the grass blade at a time. Keep mower blades sharp to prevent stress on the grass.
Fertilize Smartly: Apply nitrogen fertilizers in the right season for your grass type. Avoid excessive nitrogen during high-risk periods, especially if early signs of disease exist.
Improve Air Circulation: Aerate compacted soil to enhance drainage. Dethatch your lawn if thatch buildup exceeds ½ inch.

If you notice any of the warning signs of brown patch mentioned in this post, it is always a good idea to reach out to a professional lawn care company for help. Applying fungicides should be a last resort, and it is always most effective when performed by professionals with experience using the necessary products. If you need help treating lawn disease in the Lincoln, NE area, be sure to call Summit Lawns!