What Causes Yellow Rings in Zoysia Grass?

Yellow Patch

• Yellow patch infects zoysia lawns when temperatures are between 50 to 65 degrees Fahrenheit, according to the University of California. This fungal disease quickly germinates and spreads when weather conditions are humid and wet. If weather conditions dry out or the temperatures rise, the disease may stop spreading and grass can recover, according to the University of California. There are some instances where warm weather after infection causes symptoms to be more severe, says the University of Minnesota. However, when high humidity persists, large areas of your zoysia may become infected. Gardeners should monitor their yards for signs of damage during wet weather.

Signs

• Zoysia grass infected with yellow patch develops yellow to tan rings or patches of discolored grass. Yellow or tan discoloration can extend down the leaves. Lower leaf portions can turn purple, red or tan. Parts of the zoysia lawn may display damage for several years after yellow patch infection, according to the University of Minnesota. Gardeners must use cultural methods to treat the disease and stop it from spreading. Severe yellow patch infections should be treated with fungicides.

Cultural Treatment

• A thick thatch layer over a 1/2 inch contributes to yellow patch disease, according to the University of Minnesota. Thatch is the layer of dead and living organic matter that naturally builds up between the grass blades and soil. Zoysia grass produces more thatch than any other grass type. Check your thatch layer by cutting a 2-inch wedge-shape piece of turf out of the lawn. Remove the thatch if it is over 1/2 an inch with a power dethatcher. Rake up the diseased thatch and lawn after dethatching to prevent spreading yellow patch.

Chemical Treatment

• Treat your zoysia lawn with a fungicide that contains mancozeb, PCNB, fludioxonil or fenarimol, as suggested by the University of California. Avoid spraying water-stressed zoysia grass. To prevent the grass from becoming damaged by the fungicide, water the lawn a few days before applying the fungicide spray. Do not spray fungicides when temperatures exceed 90 degrees Fahrenheit. Repeat the fungicide spray according to the directions. Keep the lawn watered, but do not apply more water than is needed. Overwatering your zoysia lawn with more than 1 inch of water a week can encourage yellow patch.