In our area, tall fescue (a cool-season grass) is one of the most popular lawn grasses, since it stays green year-round and has good tolerance to many environmental stresses. However, in general, the species is highly susceptible to a summertime disease called brown patch, caused by Rhizoctonia solani. This fungus causes tan, roughly circular patches of turf that can range from a few inches to several feet in diameter, and it’s the only disease that causes severe damage to tall fescue on an annual basis.

During hot, humid weather, the disease is most severe, but it becomes active as soon as nighttime temperatures are above 60°F. Prolonged leaf wetness (10 or more hours) is conducive to disease development, so avoid irrigating a fescue lawn in late afternoon, before it can dry for the night.

Fungicides available

Several fungicides are available to homeowners, although these may not be as effective as products that are used by turfgrass professionals (such as lawn-care contractors) who are licensed to apply pesticides commercially. Homeowner products include those with the active ingredient myclobutanil (brand names: Fertilome F-Stop, Immunox Lawn Disease Control or Green Light Fung-Away Systemic Fungicide), propiconazole (Fertilome Liquid Systemic or Bayer Fungus Control for Lawns) or thiophanate-methyl (Scotts Lawn Fungus Control). For best control, apply the fungicide on a preventative basis when night temperatures consistently exceed 60°F, but be sure to follow the label instructions.

Depending on the weather (particularly if it turns drier), the turf may recover on its own after a couple of weeks. Also, keep in mind that other conditions (such as poor soil, turf insects, thick thatch) can also create brown patches in lawns.