Zoysia grass is a warm-season turf known for its dense growth, which naturally suppresses many competing weeds. Spreading via stolons and rhizomes, Zoysia creates a thick canopy that shades the soil, making it difficult for weed seeds to germinate. Despite this natural defense, Zoysia is still susceptible to invasion, especially when the turf is stressed or during transition periods in spring and fall. Maintaining a weed-free Zoysia lawn requires a multi-faceted approach combining cultural practices, preventative chemical control, and targeted treatments.
Foundation for Weed Control
The primary defense against weed invasion begins with maximizing the health and density of the Zoysia turf itself. Proper maintenance practices create an environment where the grass thrives, effectively outcompeting opportunistic invaders for sunlight, water, and nutrients.
Mowing height is a powerful cultural tool; maintaining Zoysia between one and two inches encourages a denser turf that shades the soil surface. Adhere to the one-third rule, removing no more than one-third of the blade height in any single session. This prevents stressing the plant and weakening its defenses.
Irrigation should be deep and infrequent, supplying approximately one inch of water per week to the lawn. This watering strategy encourages the development of extensive, deep root systems in the Zoysia, while simultaneously discouraging shallow-rooted weed species that cannot tolerate drying periods between waterings.
Zoysia’s vigorous growth often leads to excessive thatch accumulation, which can harbor pests and create an ideal seedbed for weeds. Annual core aeration and dethatching are necessary to break up soil compaction and manage this layer, ensuring healthy root access to air and water. For isolated weeds that break through, mechanical removal by hand-pulling is an effective, non-chemical solution.
Pre-Emergent Control Methods
Pre-emergent herbicides are the most effective preventative measure against annual weeds, creating a chemical barrier in the top layer of the soil. When a weed seed germinates and its root grows into this treated zone, the chemical inhibits cell division, killing the seedling before it emerges. This barrier is effective against common grassy annual weeds, such as crabgrass and goosegrass.
Selecting a product labeled safe for Zoysia is important, with active ingredients like Prodiamine, Dithiopyr, or Pendimethalin being common choices. The product must be applied evenly across the lawn and requires light irrigation shortly after application to activate the chemical barrier. Failure to water the herbicide in will leave it inactive on the surface, reducing its effectiveness.
Because the chemical barrier degrades over time, two applications per year are necessary to manage summer and winter annual weeds. The first application targets summer weeds, and a second application later focuses on preventing cool-season weeds like annual bluegrass and chickweed. Pre-emergent applications only work on seeds and will not control weeds that are already actively growing.
Post-Emergent Treatment Options
When weeds are visible and actively growing, a post-emergent herbicide is required to eliminate the established plants. These products are formulated to be selective, targeting weeds without causing damage to the Zoysia turf when used as directed. Use herbicides specifically labeled for warm-season grasses, as products intended for cool-season turf can severely damage or kill Zoysia.
For common broadleaf weeds like clover, dandelion, and spurge, combination products containing active ingredients such as 2,4-D, dicamba, and MCPP are effective. These “three-way” herbicides offer a broad spectrum of control against various broadleaf species. Specialized herbicides, including those containing sulfosulfuron or the combination product Celsius, are also safe and effective on Zoysia.
Treating difficult grassy weeds requires a targeted approach, especially for sedges like yellow nutsedge. Nutsedge must be treated with specific herbicides containing ingredients like halosulfuron (SedgeHammer) or sulfentrazone. These products are absorbed through the foliage and translocated to the roots and tubers. They require a few weeks to show full results and may need a second application to control regrowth.
Seasonal Timing for Zoysia
Timing is a factor in Zoysia weed control, dictated by the grass’s warm-season life cycle and dormancy. The spring pre-emergent application must occur before soil temperatures consistently reach 55°F, the threshold for the germination of summer annuals like crabgrass. Applying the product after this point will be ineffective, as the target weeds will have already begun to sprout.
A second pre-emergent treatment in the fall is timed to prevent winter weeds, usually when soil temperatures begin to drop below 70°F. This early fall application intercepts the germination of winter annuals, such as annual bluegrass, ensuring the lawn remains clean throughout the dormant season.
Post-emergent treatments must be applied when the Zoysia is actively growing and fully green. Avoid applications during the sensitive periods of spring green-up or fall dormancy. Applying herbicides too close to when the grass is breaking dormancy can delay its growth and cause injury. Wait at least three weeks after the turf has completely emerged from its winter dormancy before applying any post-emergent chemicals.