Spring weather – paradise conditions for large patch disease (04-17-2006)

Spring weather – paradise conditions for large patch disease

This week in our continuing discussions on warm-season lawn diseases I want to feature the fungus (Rhizoctonia solani) referred today pathologically as large patch, but previously known and commonly called brown patch.

While this disease attacks most lawn turf species, it is most serious on St. Augustine and centipede lawns in the spring and fall and considered by many as the most troublesome lawn disease for Mississippi lawns.

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 50º and 60º range with midday temperatures in the 70’s. Once summer temperatures get into the 80º to 90º 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.

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