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
- MCPA (2-methyl-4-chlorophenoxyacetic acid), dimethylamine salt
- Chemical class
- Phenoxycarboxylic acid; WSSA Group 4 synthetic auxin, which mimics a natural plant growth hormone.[2][1]
- Mode of action
- WSSA Group 4: Synthetic auxins (phenoxycarboxylic acids)[2][1]
- Signal word
- Gordon's MCPA Amine 4 (also sold as MCPA Lawn Weed Killer): Danger[1]
Spot-treating tough perennial weeds
For perennial weeds such as Canada thistle, the label mixes 4 fl oz (a quarter pint) in 3 gallons of water. Spray during active growth before bloom, and treat any regrowth.[1]
MCPA versus 2,4-D
The label notes that crops such as flax, oats and small grains underseeded with legumes tolerate MCPA better than 2,4-D. Legumes like alfalfa and clovers can still be injured or killed.[1]
Where it is used
Spray in fall or spring while weeds are young and actively growing. Thistles are best treated in the early bud stage, and perennial weeds may need a repeat application.[1]
White clover is susceptible to injury, and in some areas bentgrass, carpetgrass and St. Augustinegrass can be hurt too. Don't treat a newly seeded lawn until the grass is well established.[1]
Don't broadcast spray when air temperatures exceed 85°F; even spot treatments may cause some injury above that. Skip windy days and temperature inversions.[1]
Small amounts of drift can badly injure tomatoes, grapes, fruit trees, flowers, garden crops, shrubs and other sensitive plants, so don't spray near them.[1]
Products and registrations
| Product | Registrant | EPA Reg. No. | Active % | Formulation | Signal word |
|---|---|---|---|---|---|
| Gordon's MCPA Amine 4 (also sold as MCPA Lawn Weed Killer)[1] | PBI/Gordon Corporation | 2217-362 | 50.37% | soluble concentrate (amine salt, 4 lb MCPA acid equivalent per gallon) | Danger |
Label rates
| Product | Use | Pests | Rate |
|---|---|---|---|
| Gordon's MCPA Amine 4 (also sold as MCPA Lawn Weed Killer) | Established residential and ornamental lawns, small areas | Broadleaf weeds such as dandelion, Canada thistle, plantain, ragweed, purslane and mustards | 2 Tbsp product per 1,000 sq ft[1] Mix 2 tablespoons in 3 to 5 gallons of water and spread it evenly over 1,000 sq ft. |
| Gordon's MCPA Amine 4 (also sold as MCPA Lawn Weed Killer) | Lawns, ornamental turf and golf courses, large areas | Broadleaf weeds | 1–3 pints product per acre[1] Use 10 to 100 gallons of water per acre. No more than 3 pints per acre per application or 6 pints per acre per season, with at least 21 days between applications. |
Safety and environmental hazards
People
Signal word DANGER: the concentrate is corrosive and causes irreversible eye damage. It is harmful if swallowed or absorbed through skin, so wear goggles or a face shield, chemical-resistant gloves, long sleeves and long pants.[1]
Pets
The label's hazards to humans and domestic animals are the eye, skin and swallowing warnings. Keep others off treated areas until the spray has dried.[1]
Bees and pollinators
The label carries no bee warning; its environmental cautions concern water and drift onto sensitive plants.[1]
Fish and water
MCPA may be toxic to fish, aquatic invertebrates and aquatic plants. Don't apply to water, and avoid spraying when rain is forecast within 48 hours. It can reach groundwater through permeable soils over a shallow water table.[1]
Common questions
- How much MCPA per 1,000 square feet?
- For small lawn areas, 2 tablespoons in 3 to 5 gallons of water per 1,000 sq ft.[1]
- Will MCPA kill clover in my lawn?
- The label warns that white clover is susceptible to injury, and that legumes including clovers may be injured or killed.[1]
- Can I spray MCPA in hot weather?
- Not as a broadcast spray above 85°F. Spot treatments above that temperature may also cause some injury.[1]
Sources
- U.S. EPA Pesticide Product Label System, “Gordon's MCPA Amine 4 label, EPA Reg. No. 2217-362 (EPA-stamped, June 19, 2013).” www3.epa.gov/pesticides/chem_search/ppls/002217-00362-20130619.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)