Brown patch is a common lawn disease that affects both St. Augustine and Bahia. In South Florida, it occurs primarily in the fall and winter, but can occur in the summer as well. This fungus can cause a blade of grass to die within a matter of hours. The fungus infects the leaves closest to the soil, blocking the transport of water and nutrients to the tops of the leaves, which then die back rapidly.
The first symptom of this disease is yellowing of the leaves, or chlorosis. Affected leaves dry out and turn various shades from reddish brown to straw yellow. The fungus is most active at temperatures between 73 and 90 degrees Fahrenheit. Too much nitrogen fertilizer can encourage active growth of this fungus.
Applying a balanced fertilizer in moderate amounts is important in reducing the severity of this disease. If temperatures are favorable for disease development, free water droplets that have accumulated on the leaves due to transpiration, dew, or heavy fog should be removed. Use an irrigation system to flush away the droplets at sunrise. This will wash away the heavier droplets and allow the leaves to dry as the sun rises. If you have a small lawn area, you can pull a large hose or pole over the lawn to knock the water off the leaves.
Daconil is a good fungicide for controlling Rhizoctonia brown spot. Apply the fungicide to the affected area and a 1- to 2-foot border. Two treatments may be required for complete control.
Take-all patch disease is a serious disease brought on by the summer heat. It affects areas that were affected earlier in the year by lack of water, pests and disease problems. Summer rains provide food for the fungus, which then begins to spread. Special fungicides are needed to control the disease, and in some cases, the best treatment is to replace the area with new turf. I've written a column about this difficult-to-control disease.
Two other diseases that affect grass leaves are gray spot and rust. Both love warm, moist weather and will kill grass leaves, leaving brown leaves all over your lawn where they were once green. Unlike brown patch disease, nitrogen fertilizer will encourage new leaf growth and help your lawn recover from these leaf diseases.
Applying a fungicide will help protect the surrounding healthy grass from infection.
Ornamental diseases caused by fungi include: Root rot is most often caused by too much moisture in the soil. The plant wilts, yellows, and languishes. Stem rot affects the stems near the soil line. The stems darken, soften, and rot. They may smell bad. Leaf spots can be light to dark, small to large, and round to irregularly edged. Most leaf spots do not kill the plant, but they may cause it to drop leaves. Fungal rust spores are usually found on the undersides of the leaves. Wilt affects the plant in the water-conducting tissues, so the plant does not get water and dies. The disease can progress slowly or quickly. Powdery mildew develops on the top and bottom of the leaves. It is white at first, then turns gray. It is not always serious, and is often found in low light areas. Powdery mildew was the cause of my impatiens wilting.
To prevent disease, select healthy plants and treated seeds for planting. Remove and dispose of all dead or diseased plants and plant parts from your garden. After pruning, clean tools with a mild bleach solution to prevent tools from spreading disease from plant to plant. Leave space between plants. Thinning out dense foliage will improve air flow and speed up drying.
Fungicide applications and sprays should be done before disease begins or before the disease spreads too far. Fungicides protect healthy tissue from disease rather than curing infected tissue. Soil-borne diseases can be prevented by treating the soil with sunlight or fumigants before planting. Two good fungicides for ornamental plants are copper and systemic fungicides. Copper should be used sparingly because it can accumulate and become toxic if used frequently.
The best gardening method to prevent disease is to water early in the morning instead of in the evening. This allows the plant to dry in the sun before the water activates the fungus and spreads the disease. This process begins after 4-5 consecutive hours of moisture on the leaf surface. Many people mistakenly believe that because disease causes plant leaves or grass blades to turn brown, they must water more to make the plant or grass green again. This action only exacerbates the disease problem by providing more water to feed the fungus. If you suspect disease, dry out the area, treat it with a fungicide, and do not overdo it when watering again.
Read more: Gardening: Welcome to a subtropical summer
And: Gardening: July is not for the faint-hearted gardener.
Also: Gardening: Benefit from Proper Lawn Mowing
Peter and Eileen Ward have sold Greensward of Marco after 40 years in the lawn and landscaping business on Marco Island. If you have comments or questions about Eileen's column, please email her at Gswdmarco@comcast.net or call her at 239-269-0192.
