MSMA Weed Killer: Is It Legal and What to Use Instead

MSMA (monosodium methanearsonate) is no longer legal to use on home lawns. Under agreements with manufacturers, the US Environmental Protection Agency canceled residential turf uses of MSMA and the other organic arsenical herbicides at the end of 2009, with existing stocks allowed to be used through 2010. Today MSMA products are labeled for limited agricultural and specialty uses, chiefly cotton, not for your yard. If you have an old jug in the garage, it shouldn’t go on your lawn. The good news is that homeowners have effective, legal alternatives: quinclorac, mesotrione and fenoxaprop-based products for crabgrass, careful spot treatment and digging for dallisgrass, and halosulfuron or sulfentrazone for nutsedge. Which one fits depends on your grass type. Here’s why MSMA was restricted and what to use instead.

In this guide

1. What MSMA Is and Why It Was Popular
2. Why EPA Ended Residential MSMA Use
3. Before You Spray: Identify the Weed and Your Grass
4. Crabgrass: Legal Alternatives to MSMA
5. Dallisgrass: The Hardest MSMA Gap to Fill
6. Nutsedge: Legal Alternatives
7. A Season-Long Plan Without MSMA
8. When to Call a Lawn Care Professional
9. Using Any Lawn Herbicide Safely
10. The Long-Term Fix: Thicker Turf
11. Frequently Asked Questions

What MSMA Is and Why It Was Popular

MSMA is an organic arsenical herbicide, a relative of DSMA and cacodylic acid. For decades it was a go-to post-emergent treatment for grassy weeds in warm-season lawns, especially crabgrass, dallisgrass and nutsedge, and it was inexpensive and effective with repeat applications. University of Maryland Extension notes that herbicides containing MSMA and DSMA were classically used to control dallisgrass but are no longer labeled for use on home turf.

Why EPA Ended Residential MSMA Use

EPA’s reregistration review of the organic arsenicals found that these herbicides convert over time in soil to a more toxic form, inorganic arsenic. The agency’s main concern was that inorganic arsenic could move through runoff into sources of drinking water. In 2009, EPA reached agreements with the registrants to phase out most uses. Phase 1 canceled many uses, including residential lawns, as of December 31, 2009, with existing stocks allowed through 2010. Uses on golf courses, sod farms and highway rights-of-way were scheduled for a later phase-out under tighter restrictions, and the timing of that phase was subsequently delayed pending further EPA review. Use on cotton was retained with restrictions such as limits on applications and buffers from water bodies.

EPA’s fact sheet also noted that short-term homeowner use according to label directions did not present an imminent risk. The decision was about long-term environmental fate rather than an emergency. For homeowners the practical point is simple: no MSMA product is labeled for residential lawns, and using a pesticide in a way its label doesn’t allow is illegal.

What to Do With Old MSMA

Don’t apply it, pour it down a drain or toss it in the trash. Keep it in its original container with the label, store it out of reach, and take it to your county or city household hazardous waste collection. Your local solid waste office can tell you when and where.

Before You Spray: Identify the Weed and Your Grass

MSMA was a broad tool used across several weeds. Its replacements are more specific, so you need to know both the weed and your turf species. Crabgrass is an annual with wide, light-green blades that sprawl from a central point and dies in fall. Dallisgrass is a coarse perennial that grows in spreading clumps with yellow-green blades about half an inch wide, a pointed membranous ligule and seed stalks with three to five or more spike-like branches. Nutsedge isn’t a grass at all: it has triangular stems (roll one between your fingers), glossy blades in sets of three, and grows faster than the lawn in summer.

Your grass type matters because many herbicides injure some turf species. St. Augustine and centipede grass are especially sensitive to several crabgrass herbicides that are safe on bermuda, zoysia and cool-season lawns.

Crabgrass: Legal Alternatives to MSMA

Prevention First

The most effective crabgrass control is a pre-emergent applied in early spring before seeds germinate, usually when soil temperatures approach 55°F, with a split or follow-up application for season-long control. Common active ingredients include prodiamine, dithiopyr and pendimethalin. Dithiopyr also has some early post-emergent activity on very young crabgrass. See when to apply crabgrass preventer for regional timing.

Post-Emergent Options

Active ingredient	Works best on	Generally tolerant turf (check label)	Avoid on (check label)
Quinclorac	Crabgrass at many growth stages	Bermuda, zoysia, Kentucky bluegrass, tall fescue, perennial ryegrass	St. Augustine, centipede, bahia and some others
Mesotrione	Young crabgrass, some broadleaf weeds, nutsedge suppression	Kentucky bluegrass, tall fescue, ryegrass; some labels include St. Augustine and centipede	Bermuda, zoysia and bentgrass
Fenoxaprop	Crabgrass and goosegrass	Many cool-season lawns and zoysia	Bermuda and most other warm-season grasses
Topramezone (mostly professional)	Crabgrass, goosegrass	Cool-season turf	Bermuda and zoysia show bleaching

Turf tolerance varies by product and formulation, so read the label for your specific grass before buying. Treat crabgrass while it’s young, ideally before it tillers, and expect older plants to need a second application. Our best crabgrass killers roundup lists current homeowner products by active ingredient.

Dallisgrass: The Hardest MSMA Gap to Fill

Dallisgrass is the weed homeowners miss MSMA for most, because selective homeowner options are limited. Practical, legal approaches:

• Dig it out. UMD Extension calls hand removal or digging with a weeding tool a viable option early in an infestation and on young plants. Get the thick rhizome base, and dig when the soil is moist.
• Spot-spray and reseed. Small infestations can be sprayed with a non-selective herbicide containing glyphosate; reseed or re-sod after you’re sure of a complete kill. Expect brown patches in the lawn. Shield surrounding grass with cardboard while spraying.
• Check crabgrass product labels. UMD notes that certain post-emergent crabgrass herbicides are also labeled for dallisgrass. Read labels for a dallisgrass listing and rates for your turf.
• Bermuda lawns: some sulfonylurea-based professional products are labeled to suppress dallisgrass in bermudagrass with repeat applications. A licensed lawn care provider can apply them.
• Fix the conditions. Dallisgrass thrives in poorly drained spots. Correct drainage and keep turf dense to reduce reinfestation.

Nutsedge: Legal Alternatives

Nutsedge has better homeowner options than dallisgrass. Products based on halosulfuron or sulfentrazone, and some with imazosulfuron, are labeled for nutsedge in many turf types, including several warm-season grasses. Treat when nutsedge is actively growing, ideally before it forms new tubers in early summer, and plan a follow-up application per the label. Don’t hand-pull mature nutsedge, which leaves tubers behind to resprout. For step-by-step control, see how to get rid of nutsedge, and for product comparisons, our best weed killers roundup.

A Season-Long Plan Without MSMA

MSMA users often relied on repeated summer sprays to knock back grassy weeds. Without it, timing does more of the work. A typical warm-season lawn calendar looks like this, adjusted for your region:

• Late winter to early spring: apply a crabgrass pre-emergent before soil reaches about 55°F. Mark dallisgrass clumps while they’re easy to spot against dormant turf.
• Mid to late spring: apply the second half of a split pre-emergent if the label allows. Dig or spot-spray dallisgrass as it greens up. Watch for the first nutsedge shoots.
• Early summer: treat nutsedge while it’s young and before it sets new tubers. Spot-treat any crabgrass that escaped the pre-emergent while it’s still small.
• Mid to late summer: follow up on nutsedge and crabgrass regrowth per label intervals, but avoid spraying during heat waves or drought.
• Late summer to early fall: repair bare spots left by dead weeds by seeding, sodding or plugging, so new weeds don’t fill the gaps. In bermuda lawns, this is also when professionals target dallisgrass with repeat applications.

Cool-season lawns follow a similar pattern, with pre-emergent timed to early spring and fall the main window for seeding thin areas. Keeping a simple log of what you applied and when helps you stay within label limits on the number of applications per year.

When to Call a Lawn Care Professional

Consider a licensed lawn care provider if dallisgrass covers large areas, if your turf is a sensitive species like St. Augustine or centipede with limited homeowner options, or if repeated treatments haven’t worked. Licensed applicators can use products not sold to homeowners and can diagnose underlying drainage or soil problems.

Using Any Lawn Herbicide Safely

• Read the entire label first. It lists the turf types, weeds, rates, timing, temperature limits and protective gear. The label is the law.
• Respect temperature limits. Many post-emergent lawn herbicides can injure turf when applied above about 85–90°F.
• Spot-treat when possible rather than blanket-spraying the lawn.
• Keep people and pets off treated areas until sprays dry, as the label directs.
• Avoid drift and runoff: spray on calm days and keep products out of storm drains and water.
• Don’t spray stressed turf during drought or right after mowing or seeding unless the label allows.

Households with pets may want lower-toxicity choices; our pet-safe weed killers guide explains what’s available and the trade-offs. If you’re deciding on formulation, granular vs liquid weed killer covers when each works best.

The Long-Term Fix: Thicker Turf

Crabgrass, dallisgrass and nutsedge all exploit thin, stressed or poorly drained lawns. Mow at the high end of the recommended height for your grass, water deeply and infrequently, fertilize according to your grass type’s needs, fix drainage problems, and overseed or plug thin areas. A dense lawn shades out crabgrass seedlings and leaves less room for perennial invaders. Our lawn care guide covers the full seasonal plan.

Sources: US EPA, Organic Arsenicals fact sheet; University of Maryland Extension, Dallisgrass. Always read and follow the label of any herbicide you use.