General Yellowing From Lawn Diseases

Summer Patch

• Summer patch is a disease caused by magnaporthe poae fungal spores. Gardeners will see this disease infect their lawns in the hot summer months. Initial symptoms of infection include yellow patches of grass that extend 6 to 12 inches in diameter. As the disease progresses, the infected areas thin out and the grass takes on a bronze color. This disease is more severe in lawns that have a pH over 6.0. Fungicides that contain iprodione, azoxystrobin, cyproconazole, fenarimol or propiconazole can be used to treat the disease.

Powdery Mildew

• Powdery mildew attacks the surface of grass blades; gardeners may see a thin powdery substance cover their lawn. When powdery mildew attacks grass growing in shady areas, the disease causes the blade to turn yellow and eventually die. You may see your lawn contract powdery mildew when air temperatures are between 60 to 72 degrees Fahrenheit. Pruning back overhanging trees can increase the light in these areas and keep the disease from spreading. Fungicides can also be applied to the lawn to treat powdery mildew.

Rust

• Rust disease is more severe during hot, humid summer months. You may notice a reddish-orange dust fill the air and attach on your clothing when you mow infected turf. When rust is severe, grass blades turn yellow to reddish-orange. Lawns that have drought problems or shady areas may experience the most damage from rust. Gardeners can control the disease by watering their lawns and keeping the grass blade height at 3 inches. Reducing the amount of stress to the grass can help it overcome the infection.

Rhizoctonia Yellow Patch

• Rhizoctonia yellow patch occurs during cool moist weather conditions. New sod installed on compacted soil and thatch layers over 1/2 an inch thick can contribute to the disease. Early signs of the disease consist of yellow to light green patches of grass that are 2 to 3 inches in diameter. As the disease progresses, grass turns tan and produces discolored rings with green grass in the center. There are no fungicides to treat the disease; gardeners must try to control its spread by reducing irrigation.