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
- Bensulide
- Chemical class
- Phosphorodithioate; WSSA Group 8 fatty acid and lipid biosynthesis inhibitor. The label also names it a cholinesterase inhibitor.[2][1]
- Mode of action
- WSSA Group 8: Fatty acid and lipid biosynthesis inhibitors (phosphorodithioates)[2][1]
- Signal word
- Betamec-4 Pre-Emergence Grass Killer (Bensumec 4LF Preemergent Grass & Weed Herbicide): Caution[1]
Who can use it and where
Use is limited to residential lawns and golf course greens, tees and bentgrass fairways, not parks or other public sites. Commercial applicators must water it in or give residents bold written watering-in instructions.[1]
Broadcast only with a groundboom or low-pressure, high-volume turf gun; a low-pressure handwand is for spot treatment. It may not go through irrigation systems or be used in greenhouses.[1]
Reseeding after bensulide
Wait at least 4 months before reseeding. If you must reseed sooner, the label calls for 7 pounds of powdered activated charcoal in 14 gallons of water per 1,000 sq ft, watered in, then seeding at least 7 days later.[1]
Where it is used
It only works before weeds come up. Crabgrass emerges from the soil 4 to 6 weeks before it shows above the turf, so if weeds are already visible it is too late.[1]
Water it in right after application, for 10 to 15 minutes or ½ to 1 inch of water. The label says it won't work otherwise, and it's also a safety step.[1]
Rake up leaves, dead grass and other debris first. The label recommends it for mineral soils only and only on well-established lawns.[1]
For crabgrass, apply any time from September or October through early spring, before emergence. If germination runs into late summer, a second application 4 to 5 months later is allowed.[1]
Products and registrations
| Product | Registrant | EPA Reg. No. | Active % | Formulation | Signal word |
|---|---|---|---|---|---|
| Betamec-4 Pre-Emergence Grass Killer (Bensumec 4LF Preemergent Grass & Weed Herbicide)[1] | PBI/Gordon Corporation | 2217-696 | 46.0% | liquid concentrate (4 lb active per gallon) | Caution |
Label rates
| Product | Use | Pests | Rate |
|---|---|---|---|
| Betamec-4 Pre-Emergence Grass Killer (Bensumec 4LF Preemergent Grass & Weed Herbicide) | Established residential lawns and golf course greens, tees and bentgrass fairways | Large and smooth crabgrass, goosegrass, annual bluegrass, foxtails, barnyardgrass, fall panicum, henbit, lambsquarters, redroot pigweed and shepherdspurse | 5.6–9.4 fl oz product per 1,000 sq ft[1] 5.6 to 7.3 fl oz for crabgrass alone; 9.4 fl oz for annual bluegrass and other annual weeds, in 1.8 to 2.5 gallons of spray. The yearly maximum is 18 fl oz per 1,000 sq ft in two or more applications. |
Safety and environmental hazards
People
Signal word CAUTION: harmful if swallowed or absorbed through skin and causes moderate eye irritation. The label tells doctors it can inhibit cholinesterase, contains petroleum distillate, and may pose an aspiration pneumonia hazard.[1]
Pets
Don't let children or pets onto treated areas until the lawn has dried after watering in. The product must not be applied in a way that contacts people or pets.[1]
Bees and pollinators
Highly toxic to bees exposed to direct treatment or residues on blooming crops or weeds. Don't apply or let it drift onto blooming weeds when bees are visiting.[1]
Fish and water
Toxic to fish and aquatic invertebrates. Don't apply directly to water, and the label adds that it may impair bird reproduction if used during breeding season.[1]
Common questions
- What grasses tolerate bensulide?
- The label lists bahiagrass, bentgrass, bluegrasses, bermudagrass, centipedegrass, fescues, perennial ryegrass, redtop, St. Augustinegrass and zoysiagrass. Dichondra lawns can be treated at seeding or later.[1]
- Is bensulide the same as Betasan?
- The Betamec-4 label says the product contains Betasan, a registered Syngenta trademark, and lists bensulide as its only active ingredient at 46%.[1]
- Why does bensulide need to be watered in so quickly?
- The label says it won't work unless watered in for 10 to 15 minutes and asks for that to happen as soon as possible for safety. Keep kids and pets off until the lawn dries.[1]
Sources
- U.S. EPA Pesticide Product Label System, “Betamec-4 Pre-Emergence Grass Killer (Bensumec 4LF) label, EPA Reg. No. 2217-696 (EPA-stamped, Sept. 4, 2009).” www3.epa.gov/pesticides/chem_search/ppls/002217-00696-20090904.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)