Zoysia grass, a popular warm-season turf, is valued for its dense, carpet-like growth and resilience, which naturally helps suppress weed intrusion. Maintaining this dense turf requires a specialized approach to weed control, as Zoysia can be highly sensitive to many common herbicides safe for other grass types. The most effective strategy involves a combination of preventative measures and targeted solutions, focusing on products and timing that eliminate weeds without causing injury to the turf.
Understanding Zoysia Grass Sensitivity
Zoysia grass enters a period of dormancy during cooler months, which influences when herbicides can be safely applied. Applying chemicals while the grass is dormant or just beginning to green up can cause significant damage or delay its spring transition. Its dense growth can also be a disadvantage, as products not specifically formulated for Zoysia may struggle to penetrate the thatch layer to reach the soil or the weed’s roots. Many broadleaf herbicides contain active ingredients like 2,4-D or dicamba, which can cause temporary discoloration or severe injury to Zoysia, particularly when applied improperly or during high heat stress. Careful product selection is required to ensure the herbicide targets unwanted plants while leaving the turf unharmed.
Essential Pre-Emergent Weed Control
Pre-emergent herbicides work by creating a chemical barrier at the soil surface that prevents weed seeds from developing into mature plants after they germinate. This preventative measure addresses the problem before it becomes visible, reducing the need for aggressive post-emergent treatments later in the season. Timing the application is crucial for success. The initial application should occur in early spring, specifically when soil temperatures consistently reach between 55°F and 60°F for several consecutive days. This window targets the germination period of common summer annual weeds like crabgrass and goosegrass. Safe active ingredients for Zoysia grass include prodiamine, pendimethalin, and dithiopyr. A second application in the fall, before soil temperatures drop below 70°F, is recommended to control cool-season weeds such as annual bluegrass and chickweed. After application, the product must be lightly watered into the soil, or “activated,” to create the necessary barrier.
Targeting Existing Weeds with Post-Emergent Solutions
Post-emergent herbicides are designed to kill weeds that are already visible and actively growing. The best product depends entirely on the specific type of weed present, as no single chemical is effective against all weed categories without risking turf injury. It is important to use selective herbicides that target the weed without harming the surrounding Zoysia grass.
Broadleaf Weeds
Broadleaf weeds, such as clover, dandelion, and spurge, require specialized compounds safe for warm-season turf. Herbicides containing active ingredients like quinclorac or metsulfuron-methyl are effective for Zoysia. Quinclorac is particularly effective against certain broadleaf weeds and also controls crabgrass. For more difficult broadleaf problems, products containing a combination of selective chemicals, such as sulfonylurea herbicides, offer a wide spectrum of control while maintaining a high safety profile for Zoysia. Spot-treating individual weeds is preferred over broadcast spraying to minimize the amount of chemical applied to the turf.
Grassy Weeds
Controlling grassy weeds like crabgrass and goosegrass in Zoysia requires a different set of chemicals. Quinclorac is frequently used for tough annual grassy weeds, particularly when the weeds are young. Its dual action on both broadleaf and grassy weeds makes it a valuable tool. For managing specific, difficult grassy weeds, specialized active ingredients may be necessary. Fenoxaprop-p-ethyl is a selective post-emergent herbicide that targets grass weeds by inhibiting the enzyme acetyl-CoA carboxylase. This chemical is used for controlling grassy weeds that have matured past the stage where general post-emergents are fully effective, but label instructions must be followed precisely to avoid turf discoloration.
Optimal Application Timing and Precautions
Post-emergent chemicals should only be applied when Zoysia grass is actively growing, typically from late spring through summer. Applying herbicides when the turf is under stress, such as during drought or extreme heat, significantly increases the risk of turf injury. Avoid applying post-emergent products when air temperatures exceed 85°F, as high temperatures can increase volatility and potential damage to the Zoysia. Applying in the early morning, after dew has dried but before the heat of the day, is the most favorable time for herbicide uptake and turf safety. Users must adhere strictly to the dilution rates specified on the product label. Over-application is a common cause of turf injury, even with Zoysia-safe products. If children or pets use the lawn, they should be kept off the treated area until the spray has completely dried, which is typically a few hours.