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
- Atrazine (CAS 1912-24-9)
- 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 Auguzine St. Augustine Weed Killer (Drexel Atrazine 4%): Caution[1]
Overseeding and replanting waits
Don't overseed treated turf for 6 months, and don't replant with anything other than the listed lawn grasses for 12 months. Sprigging St. Augustinegrass or centipedegrass is allowed, though some yellowing or stunting may occur.[1]
Measure carefully
The label warns that overdosing can severely injure or kill the lawn, while too little may not control the weeds. Mix with water only, avoid overlapping passes, and use a coarse, low-pressure spray to limit drift.[1]
Where it is used
Treat in early spring or during dormancy while weeds are small or not yet up. Rain within 2 or 3 days can weaken control of emerged weeds, but preemergence control needs rain or watering within 7 to 10 days.[1]
Don't spray above 90°F or on heat- or drought-stressed grass. In summer, limit applications to spot treatments.[1]
For Florida betony, spray in mid to late October and again in mid to late February. Spurweed is best hit when newly emerged in December and January.[1]
Keep it off the root zones of trees, shrubs and vegetables, and off areas where drainage would carry it to desirable plants. Don't use it on muck or alkaline soils.[1]
Products and registrations
| Product | Registrant | EPA Reg. No. | Active % | Formulation | Signal word |
|---|---|---|---|---|---|
| Drexel Auguzine St. Augustine Weed Killer (Drexel Atrazine 4%)[1] | Drexel Chemical Company | 19713-567 | 4.0% | liquid concentrate for garden or hose-end sprayers | Caution |
Label rates
| Product | Use | Pests | Rate |
|---|---|---|---|
| Drexel Auguzine St. Augustine Weed Killer (Drexel Atrazine 4%) | Established St. Augustinegrass and centipedegrass lawns | Spurweed, Florida betony, annual bluegrass, chickweed, henbit, dollarweed (pennywort), dichondra, moneywort, clovers, sandspur, spurge; crabgrass suppression only | 8.6 fl oz product per 1,000 sq ft[1] Mix in at least 2 gallons of water per 1,000 sq ft; for small areas, 5 teaspoons in 1 quart of water covers 100 sq ft. A hose-end quart must cover at least 3,720 sq ft. No more than two applications a year. |
Safety and environmental hazards
People
Signal word CAUTION: harmful if swallowed or absorbed through skin. Wear long sleeves, long pants, waterproof chemical-resistant gloves, shoes and socks while mixing and spraying.[1]
Pets
Keep people and pets out of the area while you spray, and don't let them back onto the lawn until the spray has dried.[1]
Bees and pollinators
The label carries no direct bee warning but says the product is toxic to plants and can harm forage and habitat for pollinators near the treated site if it drifts.[1]
Fish and water
Toxic to aquatic invertebrates. Atrazine can seep through soil into groundwater used for drinking, so the label advises against using it on very permeable sand or loamy sand where the water table is shallow.[1]
Common questions
- Is atrazine restricted use?
- Not this product. The 4% St. Augustine Weed Killer is a general-use homeowner product with a CAUTION signal word and directions for garden and hose-end sprayers.[1]
- Can I use atrazine on a bermuda or fescue lawn?
- This label lists only established St. Augustinegrass and centipedegrass, and warns against use over other desirable plants.[1]
- How much atrazine weed killer per 1,000 square feet?
- 8.6 fluid ounces in at least 2 gallons of water, which matches 5 teaspoons per 100 sq ft.[1]
Sources
- U.S. EPA Pesticide Product Label System, “Drexel Auguzine St. Augustine Weed Killer (Drexel Atrazine 4%) label, EPA Reg. No. 19713-567 (EPA-stamped, Nov. 10, 2021).” www3.epa.gov/pesticides/chem_search/ppls/019713-00567-20211110.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)