Excess moisture and recent high temperatures have turned many beautiful lawns into a disease paradise. Brown patch is a sheath- and leafblighting disease caused by the fungus Rhizoctonia solani. When conditions favor brown patch disease, it is particularly severe on tall fescue. Increased use of tall fescue in home lawns and landscapes have presented a flush of inquires about the disease and control.
Brown patch develops rapidly when night temperatures exceed 70 degrees F and duration of leaf wetness exceeds 10 hours. Brown patch can be severe following extended periods of hot (70 to 90 degrees F), rainy, humid weather. High levels of available nitrogen and excess irrigation increase disease severity in tall fescue lawns.
Brown patch in tall fescue is first noticed as areas of turf resembling moisture stress, turning purple to graygreen in color. These areas quickly fade to light tan or brown as infected leaves dry out. The symptoms usually occur as discrete circular patches ranging from a few inches to several feet in diameter. More commonly symptoms occur in large thinned out areas.
Foliar symptoms are easy to see. Straw-colored foliar lesions with dark brown borders are apparent at the transition zone between healthy and diseased turf. Once the lesions have completely girdled the leaf sheath or leaf blade, the entire leaf quickly fades to tan or brown.
First reactions by many homeowners, is to apply more water. Others include additional fertilizer. Both of these practices only compound the issue making the severity of the disease worst.
Decreasing your potential for brown patch disease includes the selection of disease resistant varieties of tall fescue, maintain height of cut at 3.5 to 4 inches, maintain low to adequate levels of nitrogen applying the majority of nitrogen in the fall, maintaining adequate levels of phosphorus and potassium, and avoid excess and late afternoon or evening irrigation.
Brown patch usually infects only the leaves and leaf sheaths, so there is a high potential for recovery with moderating environmental conditions. The turf often recovers from blighting in two to four weeks without the use of fungicide. But many homeowners are unwillingly to accept the unsightly appearance of their lawn during this time. However, with extended periods of favorable weather for brown patch, the crown may also be killed.
Another option is to apply a fungicide as soon as symptoms appear. Fungicides will suppress growth and development of brown patch, but the turf will not recover from brown patch until temperatures are less favorable for the fungus and more favorable for the growth of tall fescue. Several over-thecounter lawn disease control products are available to homeowners. These products are formulated for patch-type diseases, such as brown patch, dollar spot, summer patch, etc. Be sure to follow the label for recommended preventative or curative rates of the product you choose.
REVISED: September 30, 2015