What Is Large Patch Disease?
Large patch is the most damaging disease of centipede lawns in eastern North Carolina. It can occur in St. Augustine, zoysia, and sometimes Bermuda. Excessive nitrogen fertility, improper mowing, excess thatch, poor drainage, excess watering, and/or wet, overcast days in spring, fall, or winter can lead to outbreaks of this disease. Soil temperatures between 40 and 70 degrees (Fahrenheit) are ideal for disease development. Cooler day and night temperatures have dropped soil temperatures to 70 degrees and large patch has started activity.
Large patch starts as small, circular, brown areas several inches in diameter to up to 2 feet in the fall. Large areas up to 20 feet may be killed by the spring. Damage is noticed at green up even though it occurs fall through spring in eastern NC. Affected areas do not green up like surrounding grass. These areas expand in size as temperature warms in spring and summer due to damage sustained over the fall, winter, and early spring. Damage to stems begins as water-soaked lesions followed by wilting of leaves and browning. When temperatures warm in the summer recovery occurs, but the disease spreads once favorable weather conditions return.
The best way to prevent large patch is to follow good lawn care practices, soil test, and correct drainage problems. Do not apply nitrogen fertilizers to susceptible warm season lawns with disease history before June or after August. Do not use winterizer fertilizers that contain nitrogen on warm season grasses in the fall. Water lawns only when needed. Lawns only need water when they first show drought stress by curling or graying leaves. Apply at least 1 inch of water to wet the soil to a depth of at least 4 inches.
Thatch, the layer of organic matter on top of lawn soil may make the disease worse if there is more than ½ inch. Prevent thatch buildup by mowing at the proper height for your grass and doing so frequently. For Bermuda, centipede, zoysia mow the grass to 1 to 2 inches when it gets 1.5 to 3 inches tall. Centipede needs to be mowed every 7 to 10 days when actively growing. St. Augustine should be mowed to 3 inches when it reaches 4.5 inches. These heights result in removing one third of the grass blade at any time. The smaller clippings break down fast and do not contribute to thatch buildup. Zoysia, especially cultivars like Emerald and Meyer develop more thatch due to their compact, thick growth. Zoysia lawns may need dethatching or core aerating more frequently than other lawns to prevent large patch. Dethatching or core aerating should only be done in late spring or summer when the grasses are actively growing.
Provide good surface and subsurface drainage since excess moisture is ideal for disease development. If there are low spots in your lawn that water will puddle, you can top-dress them with sand. Make sure centipede and St. Augustine leaf blades show through the sand. Top dressing is best done when warm season grasses are actively growing from May through August. Installing subsurface drainage and catch basins may help on some sites depending on soil type.
Fungicides are available for slowing the damage done by large patch. They are expensive and will not stop the disease if cultural or environmental conditions that promote it are not changed. They should be used when the disease has been previously identified in a lawn and need to be applied in the fall on lawns with a history of large patch before symptoms are seen. Lawn fungicides containing flutolanil, triadimefon, propiconazole, azoxystrobin, fluoxastrobin, or myclobutanil are available for large patch at garden centers, nurseries, retail stores or specialty stores. Liquid fungicide sprays work best. In areas with history of little damage where proper maintenance practices are in place, one to two applications 14 to 21 days apart may be enough. In severe cases applications may be needed every 14 days when soil temperatures are favorable for disease development and the lawn is still green (At least 4 applications). There is no easy cure for large patch and every yard brings a different set of growing conditions. Most large patch problems I see are related to poor drainage. This must be eliminated if you expect to see improvement. For areas with enough sun and severe large patch, the best solution may be to switch to Bermuda grass, which is more tolerant of the disease. It may still get it but the damage will be minimal compared to other grasses and Bermuda will recover quickly with hot summer temperatures.
If you have home lawn, garden, tree, or landscaping questions call the Extension Master Gardener Volunteers in Pitt County at 902-1705 or email firstname.lastname@example.org. You can visit http://pitt.ces.ncsu.edu for more local gardening information