Diseases of turf grass are a fact of life in Florida. You can avoid most diseases using proper cultural practices.
Proper cultural practices make plants healthier and will increase their tolerance to disease. Diseases mostly occur during warm weather and when there is a lot of moisture present. This moisture may be due to improper watering practices, rain, fog, or heavy dew. All of which are common this time of year.
Even though we are in the winter months, we have had some warm weather and foggy weather is normal in our winter months. This means you should keep your eyes open for diseases of the lawn.
Other problems such as insects, spilled chemicals, excess fertilizer or broken sprinkler heads can cause damage and be confused with disease. You should rule out these possibilities before assuming a disease is present. In general, diseased grass will either continue to decline or will spread to new areas. If disease is identified, you should treat with a fungicide for control as soon as possible.
Most fungicides don't cure the disease but protect the new and healthy growth in the area from infection. An application may be necessary every 10 to 14 days to keep the disease under control if conditions remain favorable for the disease. Most diseases of turf grass occur in summer months. However, brown patch is mainly a fall and winter disease in South Florida. Brown patch is caused by the fungus, Rhizoctonia solani Kuhn. It can occur in St. Augustine grass, Bermuda grass, Bahia grass, Zoysia grass and centipede grass. Affected grass blades can die in a few hours. The fungus infects the blade near the soil interrupting the transportation of water and nutrients to the grass blade, which then dies quickly. Often, damaged areas are invaded by weeds before the grass becomes healthy and regrows.
The first symptom of the disease is yellowing or wilting of the grass blades. Affected grass blades will appear dry and turn reddish brown to straw brown. The affected area is usually in a circular pattern that can grow from a few inches to several feet in diameter. Mowing and other practices can alter the shape of the affected area by spreading the fungus. When diseased blades of grass are pulled, they separate easily at the base from the rest of the plant. The bottom portion of the affected grass blades will be rotten and brown with tan to brown threads of the fungus often visible. In shady moist locations a circular pattern may not occur. Instead it may cause a thinning of the turf over a large area. A root rot may be evident. The roots will be brown and rotten instead of healthy and white.
With favorable weather, 73 to 90 degrees, the fungus grows leaf to leaf across the lawn. With high humidity and free water on leaf surfaces the fungus can spread rapidly. The disease can also be more severe in turf grass receiving excessive rates of nitrogen fertilizer.
A well- balanced, slow-release fertilizer applied at a moderate rate helps to reduce the severity of this disease. Other turf grass diseases, rust and gray leaf spot, also favor our recent warm foggy weather. They are normally prevalent in summer and fall but warm, foggy winter weather can bring on these diseases. Lawns affected with rust will have a rust-colored cast noticeable from a distance when heavily infested. Up close the dust like rust spores are in circular or long groups on grass leaves.
Rust rarely causes severe damage but can kill affected blades. Leaf spot is just that, spots on the blades which eventually cause the entire blade to die off. Stress like cold weather, which can restrict the growth of the lawn helps the development of disease. The best control for leaf disease is to keep the lawn growing rapidly by fertilizing with nitrogen and making sure you have adequate soil moisture. This is a good time of year to apply some 0-0-22 or Iron to green your winter lawn. Then keep this new growth mowed off.
Once again, treatment with a fungicide helps keep the disease from infecting the healthy new blades. Look for a fungicide labeled for control of Rhizoctonia brown patch and leaf diseases. Always water your lawn in the morning rather than the evening to prevent having free water on leaf surfaces overnight. Obviously, you cannot control the fog and rain which is why good horticultural practices and a healthy lawn go a long way to protect against diseases of the lawn this time of year.
If you suspect disease you can send a sample off to the University of Florida Plant Diagnostic Center. The submission form can be downloaded from the university web site or you can call 352-392-1795. The cost is $75 per sample.
Eileen and Peter Ward have owned a landscape and lawn maintenance company for 35 years. Eileen can be reached at Gswdmarco@comcast.net or 239-394-1413.