Brown Patch

Disease

Rhizoctonia solani

Photos

Brown patch appears as circular patches, ranging from a few inches to several feet in diameter. The infected leaves first appear water soaked and dark, eventually drying, withering, and turning dark brown. A dark smoke ring often surrounds the outer margins of the diseased area when humidity is high and disease is actively growing. Leaves in the blighted area are usually killed, and the disease can rapidly kill large areas of turfgrass in short periods of time under conducive conditions.

Brown patch survives as a saprophyte in the thatch, but when soil temperatures rise above 60° F (15-20° C), the fungus will begin to grow. While growing in a circular pattern, the fungus will begin to infect turfgrass foliage when air temperatures are above 80° F (28-30° C) and when nighttime temperatures are in the 70's (21-26° C) with high humidity.

Crops Affected: turf

Damage

The location of this disease is home lawns and golf courses. General symptoms are a patch or irregular coloring. Foliar symptoms are spots, browning, or water-soaked. This can occur during the months of June July, August, September. Hosts of the disease are Kentucky Bluegrass, Perennial Ryegrass, Tall Fescue, Fine Fescue, Creeping Bentgrass, and Annual Bluegrass.

Management

High levels of nitrogen in the field, during or just prior to the onset of hot, humid weather, is thought to increase the severity of the disease; therefore, avoiding excess nitrogen during summer months (no more than 1/2 lb per 1000 ft²), with no nitrogen applications during periods of hot humid weather.
Similar to dollar spot, the removal of dew as early as possible in the morning, or scheduling irrigation to avoid long dew periods will aide in the reduction of brown patch severity by decreasing leaf wetness duration. Improving air circulation in susceptible areas can also help to reduce disease occurrence. No genetically resistant turfgrass species or cultivars exist at this time. The most susceptible species are tall fescue, perennial ryegass, St. Augustinegrass, annual bluegrass, and creeping bentgrass.
Contact and systemic fungicides for managing brown patch are available, and are most effective when used on a preventative basis. Contact fungicides like chlorothalonil or mancozeb can manage brown patch when applied on a 7-to 10-day schedule. To be effective, they must be applied weeks before the environmental conditions for brown patch occur. Systemic fungicides like flutolanil, trifloxystrobin, pyraclostrobin, and azoxystrobin can manage the disease for up to 14-21 days. Systemic fungicides also need to be applied before the disease symptoms are evident. It should be noted that DMI fungicides, like propiconazole, fenarimol, and triadimefon, have not worked very well in controlling brown patch.