Zoysia grass is a popular warm-season turf known for its dense growth and attractive texture. Like all warm-season grasses, it is susceptible to fungal pathogens that can compromise its health and aesthetic quality. Managing these diseases depends almost entirely on the precise timing of fungicide application. Understanding when to apply a product—whether preventatively or curatively—is key to maintaining a healthy lawn.
Common Fungal Diseases in Zoysia
The most significant threat to Zoysia grass health is Large Patch, caused by the fungus Rhizoctonia solani. This infection typically appears as circular or irregularly shaped patches of sunken, brown, or straw-colored turf. A noticeable yellowish-orange border often indicates the fungus is actively spreading. Large Patch is primarily a cool-weather disease, causing damage in the spring and fall as the grass transitions into or out of winter dormancy.
Another common concern is Dollar Spot, which manifests as small, bleached spots roughly the size of a silver dollar on the turf. Closer inspection reveals distinct straw-colored lesions on the individual grass blades. This disease is favored by warm, humid conditions, extended periods of dew, and often appears in areas with low soil nitrogen levels. Identifying the specific symptoms is the first step, as different environmental conditions dictate the timing of treatment.
Preventative Timing: Applying Based on Seasonal Temperature
The most effective strategy for managing fungal diseases in Zoysia is a proactive, preventative approach timed to soil temperature, particularly for Large Patch. Preventative applications must be made before the pathogen begins to actively infect the turf. For Large Patch, the primary window for action is the autumn months when Zoysia is slowing its growth.
Fungicide treatment should begin in the fall when soil temperatures consistently decline to 70°F for five or more consecutive days. This temperature signals the start of the pathogen’s activity, which continues as long as soil temperatures remain above 50°F. A typical preventative program involves two applications spaced 21 to 28 days apart to maintain coverage throughout the high-risk fall period.
A second preventative window often opens in the spring when the soil temperature rises back into the 60°F to 70°F range, coinciding with the grass beginning to green up. Applying a systemic fungicide at this time helps protect the new growth and emerging grass from infections that may have lingered over the winter. Scheduling these applications based on soil temperature, rather than a fixed calendar date, ensures the product is present when the fungus is most likely to attack the grass crowns and roots.
Curative Timing: Applying When Symptoms Are Present
A curative application is a reactive measure taken immediately after the visual symptoms of a disease become apparent. Examples include the circular patches of Large Patch or the small spots of Dollar Spot. Speed is important in this approach, as the fungicide will stop the fungal growth but cannot reverse the damage already done to the grass blades. The goal of a curative treatment is to halt the spread of the infection and minimize further damage.
Curative treatments generally require a higher application rate than preventative treatments, and the re-application interval is often much shorter. Depending on the severity of the outbreak and the specific product label, repeat applications may be necessary every 7 to 10 days. Treatment continues until the disease is visibly under control and environmental conditions are no longer favorable for its spread. Once contained, damaged grass blades must be removed through regular mowing to allow new Zoysia growth to fill the affected area.
Practical Application Logistics
Application Preparation
Proper execution ensures the fungicide works as intended, whether the application is preventative or curative. Before applying liquid fungicide, the lawn should be mowed to one to two inches to ensure the product reaches the lower leaf sheaths and soil surface where many pathogens reside. Liquid applications require a higher volume of water, typically two to five gallons per 1,000 square feet, to facilitate thorough coverage.
Post-Application Care
For granular products and many systemic liquid fungicides, a light irrigation of approximately 1/8 inch of water immediately after application is necessary to move the active ingredient into the soil. Watering should be done in the early morning hours to allow the turf canopy to dry quickly, as prolonged moisture on the leaf surface encourages fungal growth. To combat the development of fungicide-resistant strains of fungi, rotate products with different Modes of Action (FRAC code) throughout the season.