Roundup on Dormant Zoysia for Ryegrass Control: Safety and Alternatives

A homeowner wants to kill perennial ryegrass in dormant zoysia using Roundup instead of expensive Certainty herbicide. The expert provides temperature-based guidelines and university resources.

Glyphosate on Dormant Zoysia: Conditions for Safety

• Complete dormancy required: No green tissue visible
• Temperature window: 50-80°F for absorption/translocation
• Rate: 1 oz/gal (not 3 oz/gal)—light dose
• Spot treat only: Target ryegrass patches, not broadcast
• Add surfactant: Improves coverage on waxy ryegrass leaves

Regional Validity

Guidelines based on mid-Atlantic and Kansas State research. Verify for your zone. Southern zones with incomplete dormancy risk zoysia injury.

Alternative Strategies

1. Pre-emergent (fall): Prodiamine, dithiopyr, or pendimethalin prevent ryegrass germination
2. Pre-emergent (spring): Prevent summer annuals
3. Cultural: Mow zoysia low (1") in late winter to stress ryegrass
4. Certainty (sulfosulfuron): Selective for ryegrass in zoysia; expensive but safer
5. Revolver (foramsulfuron): Professional option for transition

University Resources

• UGA Turfgrass Weed Management: commodities.caes.uga.edu/turfgrass
• Kansas State: Roundup permitted in full dormancy
• Local extension: Region-specific labels and timing

Critical Warning

If zoysia shows ANY green—even at base—glyphosate will cause injury or death. Test a small area first. When in doubt, use selective herbicides or cultural management.