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
- Mesotrione (CAS 104206-82-8)
- Chemical class
- Triketone-type HPPD inhibitor; WSSA Group 27, the group that includes triketones, isoxazoles and pyrazoles.[2][1]
- Mode of action
- WSSA Group 27: HPPD (p-hydroxyphenyl pyruvate dioxygenase) inhibitors (triketones)[2][1]
- Signal word
- Tenacity Herbicide: Caution[1]
Using it when seeding a lawn
Tenacity can go down right before or after seeding tolerant grasses, at 0.115 to 0.184 fl oz per 1,000 sq ft, to hold back weeds that slow new turf. It may thin fine fescue seedings, so use it only on blends under 20% fine or hard fescue.[1]
Don't spray newly germinated grass. Wait until the new turf has been mowed twice or is four weeks past emergence, whichever is longer, before a postemergence spray.[1]
Grasses and plants it can hurt
Bentgrass, Poa annua, kikuyugrass, zoysiagrass, seashore paspalum and bermudagrass are sensitive, except for a dormant-bermudagrass winter weed use. Keep spray off roses, daylilies and flower beds, and plant nothing but turfgrass for 18 months after the last application.[1]
Where it is used
For preemergence use, it needs 0.15 inch of rain or irrigation within 10 days to activate. For weeds already up, add a non-ionic surfactant and plan a second spray 2 to 3 weeks later.[1]
Expect temporary whitening of the lawn itself 5 to 7 days after spraying, lasting several weeks. A second application to the same spot causes less whitening.[1]
Crabgrass and goosegrass respond best postemergence when they have fewer than 4 tillers. Young, actively growing weeds die more reliably than mature or drought-stressed ones.[1]
Don't use clippings from treated turf as mulch around trees or in vegetable or flower gardens, and avoid spraying over exposed tree roots.[1]
Products and registrations
| Product | Registrant | EPA Reg. No. | Active % | Formulation | Signal word |
|---|---|---|---|---|---|
| Tenacity Herbicide[1] | Syngenta Crop Protection, LLC | 100-1267 | 40.0% | suspension concentrate (4 lb mesotrione per gallon) | Caution |
Label rates
| Product | Use | Pests | Rate |
|---|---|---|---|
| Tenacity Herbicide | Established turf and new seedings of Kentucky bluegrass, tall fescue, centipedegrass, buffalograss and other listed grasses | Crabgrass, goosegrass, yellow foxtail, nutsedge, clover, chickweed, dandelion, ground ivy, wild violet, creeping bentgrass, nimblewill and other listed weeds | 0.092–0.184 fl oz product per 1,000 sq ft[1] Equal to 4 to 8 fl oz per acre. Cap perennial ryegrass and fine fescue at 0.115 fl oz per 1,000 sq ft (5 fl oz per acre) and St. Augustinegrass sod at 0.092. No more than 16 fl oz per acre per year, with at least 14 days between sprays. |
| Tenacity Herbicide | Spot treatment of weeds in tolerant turf | Listed broadleaf and grassy weeds | 0.5 tsp product per gallon of water[1] The label's spot mix is 1 teaspoon of Tenacity and 3 teaspoons of non-ionic surfactant in 2 gallons, sprayed at 1 gallon per 1,000 sq ft. |
Safety and environmental hazards
People
Signal word CAUTION: harmful if absorbed through skin, and prolonged or repeated skin contact may cause allergic reactions in some people. Handlers wear long sleeves, long pants, shoes, socks and chemical-resistant gloves.[1]
Pets
Keep people and pets off treated areas until the spray has dried, then irrigate lightly to move product off the grass blades.[1]
Bees and pollinators
The label has no direct bee toxicity warning, but it notes the product is toxic to plants and can harm forage habitat for pollinators next to the treated site if spray drifts.[1]
Fish and water
Don't apply directly to water. Mesotrione can leach to groundwater in permeable soils with a shallow water table, and it has a high potential to reach surface water in runoff for several months.[1]
Common questions
- Why did my weeds turn white after Tenacity?
- That's how it works. Treated weeds stop growing, lose their chlorophyll and turn white, and death can take up to three weeks.[1][2]
- Can I spray mesotrione when I overseed?
- Yes, on the tolerant grasses the label lists, except fine fescue. It can be applied before or after seeding, but not onto freshly sprouted grass.[1]
- Is Tenacity safe on St. Augustine or bermuda lawns?
- Only partly. The label lists St. Augustinegrass grown for sod at a reduced 4 fl oz per acre, and calls bermudagrass sensitive except when fully dormant.[1]
Sources
- U.S. EPA Pesticide Product Label System, “Tenacity Herbicide label, EPA Reg. No. 100-1267 (EPA-stamped, Sept. 28, 2022).” www3.epa.gov/pesticides/chem_search/ppls/000100-01267-20220928.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)