Large Patch Increases with High Moisture and Fertilization (4-18-11)

The fungus (Rhizoctonia solani), commonly known as large patch or brown patch, is the most troublesome lawn disease for many Southern lawns. While this disease attacks most lawn turf species, it is most serious on St. Augustine and centipede lawns in the spring and fall.

Large patch is most severe when temperatures moderate at night in the upper 50 and 60 degree range and midday temperatures in the 70’s and low 80’s. Once summer temperatures get into the upper 80’s, and higher, disease activity ceases until fall.

As our Southern lawns transition from their dormant winter brown appearance to their renewed green growth of spring, we as homeowners often attempt to speed things along by fertilizing too early.

Large patch activity is enhanced by high nitrogen fertilization, moisture on the leaf surfaces, and excessive thatch. Therefore, to diminish the incidence of attack be judicious with spring fertilization, particularly with fertilizers high in water soluble nitrogen. We have no control over spring rain showers, but if watering is necessary, water early enough in the day to allow foliage to dry before nightfall and maintain good mowing practices to manage thatch buildup.

Visual symptoms of large patch are brownish to gray irregular circular patches often with a narrow smoke-colored ring bordering the diseased area. These water-soaked or scalded spots can spread rapidly from a few inches to several feet in size. The fungus generally attacks the base of leaf sheaths where they join to the stolons. When the disease is most active infected leaves may slip easily from the stolons when pulled and display a brown, wet, slimy decay at their base. When large patch becomes severe, fungicide applications may be necessary.

For more information on large patch and other lawn diseases refer to Establish and Manage Your Home Lawn which can be obtained from your local Extension Service office.

Published April 18, 2011

Dr. Wayne Wells is an Extension Professor and Turfgrass Specialist. His mailing address is Department of Plant and Soil Sciences, Mail Stop 9555, Mississippi State, MS 39762. wwells@ext.msstate.edu