Strategies for dealing with brown patch on lawns

Fescue and bluegrass lawns are in a fierce battle during July and August in Missouri. Potential stresses include heat, humidity, drought, brown patch disease, white grubs and crabgrass. Previous articles have provided insight on how best to deal with white grubs, crabgrass and other weedy competitors. The focus of this installment is on dealing with summer weather and disease pressure.

Hot and dry weather alternated with hot and wet weather can be a one-two punch; drought-weakened turf which is then attacked by a disease such as brown patch will fare poorly. Brown patch is favored by hot daytime (over 80 degrees F) and nighttime temperatures (over 65 degrees F) and extended periods of leaf wetness (more than 10 hours) and high humidity. Symptoms of brown patch can develop rapidly, appearing after 24 to 48 hours of favorable weather conditions. In the first stages of development diffuse areas of the lawn may appear off-color. As the disease progresses, roughly circular patches (4 to 12 inches in diameter) of blighted turf will appear. Diseased leaf blades have round to oblong straw-colored lesions with dark borders. Many people often mistake brown patch damage for drought stress and overwater affected areas making the disease worse! Take the time to look closely at the leaf blades for lesions and check the soil for adequate moisture. If brown patch is suspected, contact your local extension specialist and have them send in a sample to the MU Extension Plant Diagnostic Clinic for verification before any fungicide applications.

Proper cultural practices will help suppress brown patch development. Following proper fertilization guidelines during the year is very important. Do not apply more than 4 pounds of nitrogen per 1,000 square feet per year. Apply the majority of nitrogen from mid-September into November. Do not apply more than 1 pound in the spring and do not fertilize from June through August. Do not water until the first signs of turf wilting appear, i.e., when the turf begins to have a bluish cast and leaf blades fail to rebound from footprinting. Do not water in the early evening because this can extend the length of time the leaves are wet and susceptible to infection. Instead, try to water in early morning hours between 4 and 9 a.m. Irrigate as infrequently as possible, once or twice a week so as to restore moisture to the top 4 to 6 inches of soil. Mow at a height of 2½ to 3½ inches after the leaves have dried. Dull mower blades will shred and damage leaves predisposing them to infection.

Brown patch can be suppressed by fungicide applications, however, treatment is expensive. Here are three options:

Option 1: Don't spray any fungicides. By the time many people notice the disease, most of the damage has been done. Fungicide application at this time will not alter the amount of existing damage, although it will stop further infection. Weather conditions often change rapidly, stopping the disease naturally. Follow the above cultural practices and much of the fescue may recover in two to three weeks. Reseed severely damaged areas in the fall with a high quality turf-type tall fescue blend.

Option 2: Apply a curative fungicide such as chlorothalonil (Daconil, Thalonil, Manicure, others) or thiophanate-methyl (Cavalier) to help suppress further disease development. If the weather turns dry and cooler this fungicide may not have been needed. Protection should last for about two weeks.

Option 3: Apply a protective fungicide on a regular interval during the summer. This option is for homeowners who insist on a blemish-free lawn. Beginning in mid- to late June, apply the preventive (high) rate of triadimefon (Bayleton, Fungi-Fighter, Fungicide VII, others) at four- or five-week intervals to suppress the development of brown patch. Two or three applications should be sufficient to provide season-long control.

Erik Ervin, Turfgrass Specialist and Barbara Corwin, Director of Extension Plant Diagnostic Clinic, UMC with substantial material taken from a newsletter article by Ned Tisserat, Plant Pathologist at Kansas State University