Mysterious brown patches showing up on your lawn? Chances are, your grass has a fungal infection known as brown patch disease, caused by Rhizoctonia solani. This foliar disease appears when humid and hot, often in mid to late summer. Thankfully, it doesn’t harm the grass’ crown or the roots, but you should fix it quickly to prevent spreading.
Brown patch disease is most severe when low temperatures are above 70°F, and daytime highs climb above 90°F. For infection to occur, the blades of grass need to be continuously wet for a minimum of ten to twelve hours.
The best treatment for brown patch disease is a combination of fungicide applications and non-chemical cultural control practices that promote excellent lawn care health.
Treating with Fungicide
Spray your lawn with either a liquid or granular fungicide for brown patch to minimize spread to other areas of turf. The most commonly used products are azoxystrobin (alone or with propiconazole), pyraclostrobin, and fluoxastrobin. Apply every 14 to 28 days, and alternative fungicides every application, so the pathogen doesn’t become resistant.
One of the significant drawbacks to using a fungicide for the treatment of brown patch is cool-season grasses are growing very slowly when it’s hot. This slow growth may make fungicides ineffective because these grass types go dormant when it’s hot, and they can’t recover from the damage until they are actively growing.
The following practices are best when used in conjunction with fungicide applications. They help improve overall lawn health and minimize conditions that favor brown patch disease.
- Aerate and dethatch the turf to improve air circulation through the grass, reducing the humidity levels close to the soil.
- Do not mow infected areas or cut them last to prevent spreading spores through infected grass clippings.
- Avoid walking through brown patch areas to keep from dispersing spores on your shoes.
- Do not apply fertilizer, especially nitrogen, during a disease outbreak, as it feeds the fungus.
- Maintain soil pH above 6.0, preferably keeping it between 6.5 and neutral (7.0).
- Keep soil potassium and calcium at the higher end of “sufficient levels” without overapplying.
- Mow your turf at its recommended height. If you cut the blades too short, it stresses the grass, making it more susceptible to diseases. Mowing the grass too high maintains higher humidity levels.
- Do not clip off more than a third of the blade during any mowing event to slow thatch accumulation.