April showers bring large patch fungus, too (4-20-09)

While the age old slogan of “April Showers Bring May Flowers” reminds of us that spring has arrived and our lawns and landscapes burst back to life with new growth and color, it also should remind us that these afternoon showers may enhance lawn fungal diseases.

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

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

Brown patch is most severe when temperatures moderate at night in the upper 50 and 60 degree range with midday temperatures in the 70’s. Once summer temperatures get into the 80 and 90-degree range disease activity ceases until fall. Brown 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; water early enough in the day to allow foliage to dry before nightfall; and maintain good mowing practices to manage thatch buildup.

When large patch becomes severe applications of fungicides may be necessary.

Published April 20, 2009

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. [email protected]