Many conditions can cause patches of brown, dead grass on your lawn, but only one gets the official name "brown patch." Brown patch disease is a condition caused by a Rhizoctonia fungus, usually Rhizoctonia solani. The fungus often appears in mid- to late-summer when the weather is hot and humid. Brown patch is a foliar disease, meaning that it harms the blades of grass but not the crown of the plant or the root system. Grass plants affected by brown patch may recover on their own, without chemical intervention.
Rhizoctonia can affect all cool-season lawn grasses, but it is especially harmful to ryegrass and tall fescue. Kentucky bluegrass and fine fescues can occasionally be affected, but the damage is usually minimal in these species. Brown patch can also affect a variety of warm-season grasses, including St. Augustine grass and zoysiagrass.
When to Get Rid of Brown Patch Fungus
Begin your efforts at brown patch control in the spring, with aeration and dethatching. Application of fungicide should be done when the fungal patches appear, usually mid to late summer, Reseeding with different grass species, where necessary, can be done by over-seeding over several fall seasons, or, if you want quicker results, eliminate the old turf grasses in spring and reseed immediately.
Before Getting Started
The Rhizoctonia fungus may be present for some time in the soil before it manifests as brown patch disease. The fungus overwinters in the lawn grass or soil beneath in the form of fungal bodies known as sclerotia, and it can survive for years until conditions are right. Rhizoctonia is most likely to cause brown patch during the periods of high temperature and high humidity in mid- to late-summer when night-time temperatures remain above 68 degrees Fahrenheit and daytime temperatures are routinely in the 80s or above. Periods of rainy weather when the air is saturated with moisture also promote the appearance of the disease.
In addition to heat and humidity, the main factors inviting brown patch are excessive nitrogen and irrigation, which means that very lush and green lawns can be susceptible to brown patch. Other causal factors include lack of air movement, poor soil drainage, excessive thatch, and compacted soils, which means that poorly maintained lawns can also be prone to brown patch disease.
Fungicide powders and sprays are typically not as toxic to pets and humans as most herbicides and pesticides, but some are known to irritate eyes, and other formulations can cause throat irriation and coughing if they are inhaled. More severe health problems are possible for individuals who use fungicides repeatedly or who have high exposure.
Equipment / Tools
- Bow rake or dethatcher
- Lawn aerator (can be rented)
- Pressure sprayer
- Lawn fungicide (if needed)
- Fungus-resistant grass seed (if needed)
Eradicating brown patch disease may not require all of the following steps. You can stop work when the efforts show results. The time and effort required will depend entirely on the severity and persistence of the infestation—minor problems may be very easy to solve, while combatting widespread infestation can be a year-long endeavor. Always try to control brown patch fungus by adjusting cultural practices before reaching for chemical fungicides.
Diagnose the Disease
Brown patch appears as irregular circular patches in the lawn that are brownish-yellow in color and range from 6 inches to several feet in diameter. The affected leaves usually remain upright, and close inspection shows lesions on the leaves that are tan in color and irregular in shape with a dark brown border. White, cottony, mycelium can be found on dew-covered turf in the early part of the morning.
The ring itself is most visible in the morning. Sometimes grass within the ring is entirely killed, creating a sunken look to the patch, but more often the grass inside the patch simply becomes thinner than the surrounding lawn.
Improve Air Circulation
Many cases of brown patch can be cured simply by improving air circulation in the lawn, which reduces the humidity that favors the fungus. The best way to do this is to aerate and dethatch the lawn annually.
Dethatching can be done manually, with a stiff bow rake or dethatching rake, or with power equipment available for lease at home centers and tool rental outlets. Aeration is normally done with a power rental tool, or by a hired professional lawn service.
Change Cultural Practices
Brown patch fungus thrives in wet, fertile conditions, so the response to ongoing lawn problems is to reduce feeding of your lawn and make sure watering practices are appropriate.
Avoid feeding your lawn during hot and humid weather, and reduce the amounts of fertilizer used. Fertilizer manufacturers often recommend repeated heavy feedings, but your lawn is often healthier with just one or two light feedings each year.
Watering is probably not necessary at all if you are getting 1 inch of rainfall per week, But if you do water, do it early in the day so the grass can dry out fully before nightfall. If dew is collecting on your lawn each morning, your lawn probably does not need to be irrigated at all. Standing dew can be removed by dragging a water hose over the lawn, which will lower the humidity that causes brown patch disease.
Lawn care experts say that fungicide treatment is appropriate only for high-value ryegrass and bentgrass turf blends; most lawns typically recover without chemical treatments.
The first spray of fungicide should be applied immediately after the symptoms first appear, especially if hot and humid weather is expected. Although fungicides can be purchased by homeowners, it's best to deal with a lawn care company staffed by professionals who are trained to diagnose and treat lawn diseases.
As this any chemical application, it's best to spot-treat diseased areas rather than apply chemicals broadly over the entire lawn.
Reseed With Resistant Grass Varieties
Where all other efforts fail you may need to reseed with a turfgrass variety that has known resistance to this fungus. A variety of grasses are available with moderate resistance to the Rhizoctonia fungus. If a brown patch is an annual occurrence, consider top-seeding your lawn with resistant grasses. Check with your local university extension service on recommendations for resistant grass species.
Brown Patch, Yellow Patch, and other Rhizoctonia Leaf and Sheath Spot Diseases of Turfgrass. University of Massachuetts Amherst Extension