Hot humid weather ideal environment for gray leaf spot (6-28-10)

Gray leaf spot (Pyricularia grisea) is a fungal turf disease primarily attacking St. Augustine lawns during extended periods of hot humid weather, but centipede lawns are also susceptible. The fungus causes irregular gray or dirty-yellow spots with brown, purple, or water soaked borders on leaf blades. In areas of heavy disease development, the grass blades may have a burned or scorched appearance similar to pouring scalding hot water across the lawn that results in death or spotting of leaf blades. Shaded areas that stay wet longer are usually the first to be attacked. The fungus thrives when air temperatures are above 70 degrees.

Gray leaf spot is best managed by 1) avoiding high nitrogen fertilization, especially water-soluble nitrogen, in summer wet periods, 2) watering properly so foliage doesn’t stay wet for extended periods, 3) mowing when leaves are dry and maintaining optimum height, 4) applying repeated applications of appropriate fungicides during warm wet periods.

For a current list of labeled fungicides for homeowner use consult the homeowner fungicide database at http://www.extensionplantclinics.msstate.edu.

Published June 28, 2010

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