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
- Fluridone
- Chemical class
- Pyridinone; WSSA Group 12 carotenoid biosynthesis inhibitor (phytoene desaturase).[2][1]
- Mode of action
- WSSA Group 12: Carotenoid biosynthesis inhibitors (phytoene desaturase)[2][1]
- Signal word
- Sonar A.S. Aquatic Herbicide: Caution[1]
What it won't control
Algae, including chara, nitella and filamentous species, are not controlled. Neither are waterhyacinth, waterlettuce, arrowhead, pickerelweed, bulrush, rush, water pennywort, American frogbit or maidencane.[1]
Cattail, alligatorweed, American lotus, parrotfeather, watershield, salvinia and torpedograss are only partly controlled.[1]
Irrigating with treated water
Water from treated ponds can injure irrigated plants. Wait 7 days before watering established crops or trees and 30 days for established turf. Newly seeded areas and tomatoes or peppers need a water test showing 5 ppb or less.[1]
Where it is used
Keep it in contact with target plants for at least 45 days. Flowing water or anything else that quickly dilutes the treatment will weaken results.[1]
Apply before weeds start growing or as they begin active growth. White or pink growing tips show up in 7 to 10 days, but full control takes 30 to 90 days.[1]
Measure the acreage and average depth first. Quarts per surface acre equal average depth in feet times the target ppb times 0.0027.[1]
Treating small patches or narrow boat lanes in a big lake often fails because untreated water dilutes it; lake treatment areas should be at least 5 acres.[1]
Products and registrations
| Product | Registrant | EPA Reg. No. | Active % | Formulation | Signal word |
|---|---|---|---|---|---|
| Sonar A.S. Aquatic Herbicide[1] | SePRO Corporation | 67690-4 | 41.7% | aqueous suspension (4 lb active per gallon) | Caution |
Label rates
| Product | Use | Pests | Rate |
|---|---|---|---|
| Sonar A.S. Aquatic Herbicide | Freshwater ponds of 10 acres or less, whole-pond treatment | Hydrilla, Eurasian and other watermilfoils, coontail, elodea, egeria, fanwort, naiad, most pondweeds, bladderwort, duckweed, water-lily and spatterdock | 3.8–7.7 fl oz product per treated surface acre per foot of average depth[1] This targets 45 to 90 ppb. Multiply by the pond's average depth in feet: a 4-foot-deep pond takes 15.7 to 31.4 fl oz per surface acre. All applications together may not exceed 90 ppb per growth cycle. |
Safety and environmental hazards
People
Signal word CAUTION: harmful if swallowed, absorbed through skin or inhaled. Avoid breathing spray mist; gloves are required when mixing and applying with a hand wand to ponds or lakes.[1]
Pets
At label rates up to 150 ppb the label sets no waiting period for swimming, fishing, drinking water, or livestock and pet drinking.[1]
Bees and pollinators
No direct bee warning, but the label says it is toxic to plants and can harm forage and habitat for pollinators beside the treated site through drift.[1]
Fish and water
It is meant for water, so it isn't for tidewater or brackish sites. Use the lowest rates in shallow shoreline areas, and expect occasional yellowing of trees and shrubs growing in treated water.[1]
Common questions
- Can I swim or fish after treating with Sonar?
- Yes. At 150 ppb or less, the label lists zero days of restriction for swimming, fishing, drinking water and livestock or pet drinking.[1]
- How fast does fluridone work on pond weeds?
- Slowly. Symptoms appear in 7 to 10 days, and the desired level of control usually takes 30 to 90 days.[1]
- Does Sonar kill pond algae?
- No. The label states chara, nitella and filamentous algae are not controlled, though it may be tank mixed with algaecides.[1]
Sources
- U.S. EPA Pesticide Product Label System, “Sonar A.S. Aquatic Herbicide label, EPA Reg. No. 67690-4 (EPA-stamped, Feb. 3, 2023).” www3.epa.gov/pesticides/chem_search/ppls/067690-00004-20230203.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)