The label is the law. Read your product's label before you mix or apply; the rates here come from the labels listed under Sources.
- Active ingredient
- Mecoprop-p (MCPP-p), dimethylamine salt (CAS 16484-77-8 (mecoprop-p acid))
- Chemical class
- Phenoxy herbicide; current products contain the single active isomer, mecoprop-p.[1]
- Mode of action
- WSSA Group 4: Synthetic auxins (phenoxycarboxylic acids): act like the plant hormone auxin[3][1]
- Signal word
- Riverdale MCPP-p 4 Amine: Caution[1]
How it works
Mecoprop mimics a plant growth hormone and interferes with plant cell formation, causing abnormal growth.[2]
WSSA places the phenoxycarboxylic acids in Group 4, the synthetic auxins, which act like the plant hormone auxin even though the exact mechanism is not well understood.[3]
Protecting the rest of the yard
Do not use it on or near desirable plants, including within the dripline of trees and shrubs, do not let spray drift onto them, do not apply it through irrigation systems, and do not use the first grass clippings after treatment as mulch for flowers or vegetables.[1]
Where it is used
This product is for lawns, golf courses and ornamental turf; it is relatively slow-acting but controls harder broadleaf weeds such as clover, mouseear chickweed and thistle.[1]
It is not recommended for St. Augustinegrass or centipedegrass because it can damage them, and it should not be used on newly sown lawns until the grass is well established; reseed no sooner than three to four weeks after treatment.[1]
Products and registrations
| Product | Registrant | EPA Reg. No. | Active % | Formulation | Signal word |
|---|---|---|---|---|---|
| Riverdale MCPP-p 4 Amine[1] | Nufarm Americas Inc. | 228-192 | 26.0% | liquid (1.9 lb mecoprop-p acid per gallon) | Caution |
Label rates
| Product | Use | Pests | Rate |
|---|---|---|---|
| Riverdale MCPP-p 4 Amine | Established lawns and golf fairways | Clover, chickweed, dandelion, plantain, ground ivy, spurge, thistle and other listed broadleaf weeds | 1.5 fl oz per 2.5 gal of water per 1,000 sq ft[1] Broadcast: no more than 3 pints per acre per application and no more than 2 applications per year, at least 30 days apart. |
| Riverdale MCPP-p 4 Amine | Established greens | Listed broadleaf weeds | 1.0 fl oz per 2.5 gal of water per 1,000 sq ft[1] Bentgrass greens; see label for grass tolerances. |
How to apply it, step by step
1. Protective gear
- Wear a long-sleeved shirt and long pants, and shoes and socks; it causes moderate eye irritation and may be harmful if swallowed. Throw away clothing soaked with the concentrate.[1]
2. Before you spray
- It controls broadleaf weeds in established cool-season lawns; it isn't recommended for St. Augustinegrass or centipedegrass, and not on newly sown lawns until the grass is well established.[1]
- Spray when weeds are growing vigorously, not during drought or above 90°F when fine grasses are more easily injured, and not if rain is likely.[1]
- Don't mow for 2 or 3 days before or after treatment. Keep it away from flowers, shrubs, trees (including their root zones) and vegetables; even invisible drift can badly injure them. Don't use it near a well or cistern.[1]
3. Mixing
- Mix 1½ fl oz in 2½ gallons of water for each 1,000 sq ft of established lawn.[1]
4. Applying
- Spray the mix evenly over the 1,000 sq ft with a medium or coarse spray.[1]
- For harder-to-kill weeds, a repeat at half the rate can follow within 30 days; otherwise allow at least 30 days between applications and no more than 2 a year.[1]
5. After you spray
- Stay off the lawn until the spray has dried, and don't water for at least 24 hours.[1]
- Wait 3 to 4 weeks before reseeding, and don't use the first clippings as mulch for flowers or vegetables.[1]
First aid
- In the eyes, hold them open and rinse slowly and gently for 15 to 20 minutes, removing contact lenses after the first 5 minutes, and call a poison control center or doctor.[1]
- If swallowed, call a poison control center or doctor right away, have the person sip water if they can swallow, and don't induce vomiting unless told to. Medical emergencies: 1-877-325-1840; spills: CHEMTREC, 1-800-424-9300.[1]
Storage, spills and disposal
- Store it tightly sealed in a secure place above 32°F (if it freezes, remix before use), away from seed, fertilizers and other pesticides; open it in a well-ventilated area.[1]
- Contain any spill, absorb it with sand or granules, and put it in a closed, labeled container for disposal.[1]
From the safety data sheet
- The concentrate is a transparent, light amber liquid with an amine-like odor.[4]
- The SDS uses the signal word Warning: it is harmful if swallowed and causes serious eye irritation.[4]
- Wear eye protection, wash thoroughly after handling, and don't eat, drink or smoke while using it; if it gets in the eyes, rinse cautiously with water for several minutes and get medical advice if irritation persists.[4]
- If pesticide gets inside your clothing or protective equipment, remove it right away and wash.[4]
- Store it in a secure place away from fertilizer, seed and other pesticides, with the container tightly sealed when not in use.[4]
Safety and environmental hazards
People
The label signal word is CAUTION: it causes moderate eye irritation and may be harmful if swallowed; handlers must wear long sleeves, long pants, shoes and socks.[1]
Pets
The label says not to enter or allow entry into treated areas until sprays have dried.[1]
Bees and pollinators
This herbicide label carries no bee-hazard statement; its environmental warning is that it may harm non-target plants.[1]
Fish and water
The label says not to apply it directly to water or where surface water is present, and warns that it has properties of chemicals found in groundwater, so use on permeable soils with a shallow water table or near a well or cistern may contaminate water.[1]
Common questions
- Can I use MCPP on St. Augustine grass?
- No. The label says it is not recommended for St. Augustinegrass or centipedegrass because it can damage them.[1]
- How much MCPP per 1,000 square feet?
- For established lawns the label rate is 1 1/2 fluid ounces in 2 1/2 gallons of water per 1,000 square feet.[1]
- When can kids and pets go back on the lawn?
- After the spray has dried; the label says not to enter or allow entry until sprays have dried.[1]
Sources
- U.S. EPA Pesticide Product Label System, “Riverdale MCPP-p 4 Amine label, EPA Reg. No. 228-192 (EPA-stamped, Dec. 18, 2014).” www3.epa.gov/pesticides/chem_search/ppls/000228-00192-20141218.pdf (accessed 2026-10-06)
- University of California Statewide IPM Program, “Home and Landscape Pesticide Active Ingredients Database: mecoprop.” ipm.ucanr.edu/home-and-landscape/pesticide-active-ingredients-database/active-ingredient-details/?uaiKey=32 (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)
- Nufarm Americas Inc. (Riverdale), “MCPP-p 4 Amine Safety Data Sheet (Riverdale/Nufarm, issued April 14, 2015; EPA Reg. No. 228-192, the label on this page; copy hosted by Farmers Business Network).” www.fbn.com/api/store/market/documents/sds/mcpp-p-4-amine.pdf (accessed 2026-10-17)