Crabgrass is a summer annual weed that invades stressed lawns, germinating and growing aggressively during the warmest months before dying with the first frost. Zoysia grass is a dense, warm-season turf that provides excellent defense against weeds, but its sensitivity to many herbicides requires a specific control approach. Eliminating this weed involves cultural care, precise pre-emergent timing, and selective post-emergent chemistry. The challenge is applying treatments strong enough to kill the weed without damaging the Zoysia grass.
Cultural Practices to Suppress Crabgrass
A thick, healthy Zoysia lawn is the most effective defense against crabgrass, which thrives in thin, bare patches. You can help your turf naturally outcompete the weed by managing mowing, watering, and fertilization practices.
To maximize Zoysia’s density and shade the soil surface, maintain a mowing height between 3/4 and 1.5 inches during the active growing season. Taller grass blades prevent sunlight from reaching the soil, which is necessary for crabgrass seeds to germinate. Always use a sharp blade and never remove more than one-third of the blade height in a single mowing session to avoid stressing the turf.
Proper watering techniques promote deep root growth in Zoysia, making it more resilient. Water deeply and infrequently, aiming to wet the soil to a depth of four to six inches. This practice keeps the upper layer of soil drier, which discourages the germination of crabgrass seeds that require consistent surface moisture.
Strategic fertilization strengthens the Zoysia without simultaneously feeding the emerging weed. Apply nitrogen-rich fertilizer in late spring or early summer, after the Zoysia has fully greened up and is actively growing. This timing ensures the nutrients benefit the turf’s natural growth cycle, helping it thicken and crowd out potential crabgrass seedlings.
The Timing and Strategy of Pre-Emergent Control
Pre-emergent herbicides are the most important component of a crabgrass control program because they prevent the weed from ever sprouting. These products establish a chemical barrier in the soil that inhibits the germination of crabgrass seeds. They must be applied before the weed begins to grow, making timing critical.
The most precise indicator for application is the soil temperature, not a specific date on the calendar. Crabgrass seeds begin to germinate when the soil temperature at a four-inch depth consistently reaches 55 degrees Fahrenheit for several consecutive days. A common natural cue is when the forsythia shrub finishes blooming, which often coincides with the correct soil temperature threshold.
When selecting a pre-emergent product, choose active ingredients that are safe for Zoysia turf, such as prodiamine or pendimethalin. Dithiopyr-based products are also effective and offer the added benefit of controlling crabgrass even after it has just begun to emerge. Always follow the manufacturer’s directions for application rates specific to Zoysia grass.
To ensure season-long protection, consider a split application strategy for the pre-emergent herbicide. This involves applying a half-dose of the product in the early spring at the 55-degree soil temperature mark, followed by a second half-dose six to eight weeks later. This second application extends the protective barrier through the summer months when crabgrass pressure is highest. Pre-emergent herbicides inhibit all seed germination, so avoid application if you plan to overseed or plug Zoysia within the following three to four months.
Post-Emergent Treatment Options Safe for Zoysia
Post-emergent herbicides are necessary to control any crabgrass plants that manage to break through the pre-emergent barrier. These chemical treatments target the existing, actively growing weed. When crabgrass has already sprouted, use selective herbicides that will kill the weed without harming the Zoysia turf.
Herbicides containing quinclorac are highly effective post-emergent options and are generally safe for Zoysia grass. Another appropriate active ingredient is fenoxaprop-based chemistry, which specifically targets grassy weeds like crabgrass. These products are most effective when applied early, ideally when the crabgrass is still young and has only two to four leaves.
A second application 10 to 14 days after the first treatment is often required to achieve complete control, especially for more mature crabgrass plants. Users must exercise caution regarding temperature, as applying these chemicals during extreme heat can cause damage to the Zoysia. Avoid post-emergent treatments when air temperatures exceed 85 degrees Fahrenheit to prevent injury to the lawn.
To minimize the use of chemicals and stress on the healthy turf, use a spot treatment approach for isolated patches of crabgrass. This technique involves spraying only the visible weed, rather than broadcasting the product over the entire lawn. Applying treatments with precision ensures that the surrounding Zoysia remains unaffected.