My St. Augustine Grass Is Dying With Fungus

Brown Patch

• Brown patch disease is at its most active when temperatures dip below 80 degrees Fahrenheit. St. Augustine grass becomes infected with the fungal spores that cause brown patch when humidity levels are high for 48 hours. Lawns infected with brown patch exhibit symptoms, such as the grass turning yellow to reddish-brown then straw-colored. Eventually, these patches of discolored grass will extend to 12 inches in diameter. Upon closer examination of your St. Augustine grass blades, you may see black rot where the stem and grass blade meet.

Management

• To manage brown patch, check your thatch layer. A thatch layer around 0.75 of an inch encourages brown patch. Cut a 2-inch wedge of turf out of your St. Augustine yard to check. Mow the lawn and use a power de-thatcher to remove the thatch layer. Avoid using an excessive amount of nitrogen from November through April. You can prevent and treat lawns infected with brown patch by using fungicides that contain propiconazole, thiophanate methyl, mycobutanil or azoxystrobin, according to the University of Florida.

Gray Leaf Spot

• Gray leaf spot easily infects St. Augustine lawns when the weather conditions are humid and warm. Unlike other grass types, St. Augustine is the only turf type susceptible to this disease, according to the University of Florida. Gardeners may see their grass develop small brown lesions on blades in the early phase of gray leaf spot. As the disease progresses, these spots enlarge and turn gray. Severely infected lawns begin to thin or die out from the disease.

Management

• The fungal spores that cause gray leaf spot are almost always present in St. Augustine lawns. However, gardeners will inadvertently encourage a damaging infection if they use quick-release nitrogen fertilizer frequently. Quick-release nitrogen fertilizer encourages a flush of growth that weakens the root systems of the grass. In addition, avoid mowing your lawn when the grass is wet. Your mower's blades wound St. Augustine grass blades, which creates an entryway for gray spot fungal spores. Fungicides that contain propiconazole, thiophanate methyl or triadimefon can be used to treat the disease.