The label is the law. Rates and restrictions below are taken from the product labels listed under Sources. Your product's own label governs; read it before you mix or apply. Mixing calculator · Disclaimer
- Active ingredient
- Simazine
- Chemical class
- Triazine; WSSA Group 5 photosystem II inhibitor.[2][1]
- Mode of action
- WSSA Group 5: Photosystem II inhibitors (triazines)[2][1]
- Signal word
- Drexel Simazine 4L Herbicide: Caution[1]
Overseeding and yellowing
Don't seed or overseed desirable turfgrass within 4 months before or 6 months after treatment. Newly sprigged grass, hybrid bermudagrass and non-dormant bermuda or zoysia may slow down and yellow for a while.[1]
Why water matters
The label explains that simazine enters weeds mainly through their roots, so moisture is needed to carry it into the root zone. Very dry soil after application may mean you need to water.[1]
Where it is used
For winter annual weeds, apply after September 1, or after October 1 for annual bluegrass, before they emerge. For summer annuals, apply in late winter before they come up.[1]
Water in with half an inch if rain doesn't fall within 10 days. A follow-up of 1.2 fl oz per 1,000 sq ft for later summer annuals must be at least 30 days after the first and not after June 1.[1]
Use it only on warm-season lawns, never on golf greens, muck or alkaline soils, or soils above pH 7.8. The label also bars use north of North Carolina except coastal Virginia.[1]
Don't apply over the root zones of trees or ornamentals not on the label. Newly seeded grass must overwinter and form a good rhizome system first.[1]
Products and registrations
| Product | Registrant | EPA Reg. No. | Active % | Formulation | Signal word |
|---|---|---|---|---|---|
| Drexel Simazine 4L Herbicide[1] | Drexel Chemical Company | 19713-60 | 42.1% | flowable liquid (4 lb simazine per gallon) | Caution |
Label rates
| Product | Use | Pests | Rate |
|---|---|---|---|
| Drexel Simazine 4L Herbicide | Warm-season lawns: bermudagrass, centipedegrass, St. Augustinegrass and zoysiagrass | Annual bluegrass, chickweeds, henbit, burclover, hop clover, corn speedwell, lawn burweed (spurweed), crabgrass and other annual weeds | 0.5–1.2 fl oz product per 1,000 sq ft[1] 0.75 fl oz where annual bluegrass is the main weed and 0.75 to 1.2 fl oz for other weeds, followed by 0.5 inch of watering. Without watering, use 0.5 fl oz. Two applications a year at most. |
Safety and environmental hazards
People
Signal word CAUTION: causes moderate eye irritation and is harmful if absorbed through skin or swallowed. Wear long sleeves, long pants, shoes plus socks and chemical-resistant gloves.[1]
Pets
Keep people and pets out of the area during application, and don't let them back in until the spray has dried. Don't feed turf clippings to animals.[1]
Bees and pollinators
There is no direct bee warning. The label says it is toxic to plants and can harm forage and habitat for pollinators near the treated site.[1]
Fish and water
Toxic to aquatic invertebrates. Simazine has been found in groundwater, so the label advises against using it on sand or loamy sand where the water table is close to the surface.[1]
Common questions
- Can I use simazine on a fescue or bluegrass lawn?
- No. The turf directions are only for warm-season grasses such as bermudagrass, centipedegrass, St. Augustinegrass and zoysiagrass.[1]
- How much Simazine 4L per 1,000 square feet?
- 0.5 to 1.2 fl oz depending on the weeds and whether you water it in; 1.2 fl oz is the most per application.[1]
- Is simazine restricted use?
- This Drexel Simazine 4L label is not a restricted-use product and carries the signal word CAUTION.[1]
Sources
- U.S. EPA Pesticide Product Label System, “Drexel Simazine 4L Herbicide label, EPA Reg. No. 19713-60 (EPA-stamped, Sept. 15, 2025).” www3.epa.gov/pesticides/chem_search/ppls/019713-00060-20250915.pdf (accessed 2026-10-06)
- Weed Science Society of America, “Summary of Herbicide Mechanism of Action According to the Weed Science Society of America.” wssa.net/wp-content/uploads/WSSA-Mechanism-of-Action.pdf (accessed 2026-10-06)