MCPP (mecoprop-p) is a selective broadleaf herbicide that you have almost certainly used without knowing it. It is the third ingredient in nearly every three-way lawn herbicide mix (2,4-D + dicamba + MCPP). It fills gaps in the weed spectrum that 2,4-D and dicamba miss, particularly clover and chickweed.
Clover (primary advantage over 2,4-D alone), chickweed, ground ivy, plantain, dandelion, henbit, spurge, black medic, purslane, wild carrot. MCPP is rarely used alone - its value is in the three-way combination with 2,4-D and dicamba for broadest possible weed spectrum.
You will almost never see MCPP sold as a standalone product. It is a component of: Trimec Classic (2,4-D + dicamba + MCPP), Weed B Gon (Ortho), Spectracide Weed Stop, Speed Zone (PBI/Gordon), Three Way Selective (Lesco), and virtually every consumer broadleaf lawn herbicide on the shelf. Check the active ingredients - if it lists three AI percentages, the third is almost always MCPP or MCPA.
Low to moderate mammalian toxicity. Similar safety profile to 2,4-D. Keep children and pets off treated lawn until dry. Apply in calm conditions to prevent drift to ornamental plantings.
MCPP is considered less volatile than dicamba and less likely to cause off-target drift damage. This is one reason it remains a preferred third component in three-way mixes.
Why three-way mixes exist: No single broadleaf herbicide controls every weed species. 2,4-D is excellent on dandelions but weak on clover. Dicamba handles tough weeds like ground ivy but has drift issues. MCPP fills the remaining gaps - particularly clover, chickweed, and black medic. Together, the three cover virtually every common lawn weed.
The clover question (again): MCPP is the primary clover-killing component in lawn herbicides. If you WANT to keep clover in your lawn (increasingly popular for nitrogen fixation and pollinator habitat), you need to avoid products containing MCPP - which means avoiding almost all consumer broadleaf herbicides. Spot-treatment with straight 2,4-D amine is one option that will kill dandelions while sparing clover, but it is harder to find as a consumer product.
MCPP vs MCPA: Some products substitute MCPA for MCPP. Both are phenoxy herbicides with similar weed spectrums. MCPA is slightly less effective on chickweed but slightly better on certain weeds like buttercup. For practical homeowner purposes, they are interchangeable.
Application timing: Three-way mixes containing MCPP follow the same timing rules as 2,4-D: apply to actively growing weeds when temperatures are 60-80F, do not mow for 2-3 days before or after, and do not apply during drought stress. Fall applications (September-October) often give the best results because weeds are transporting nutrients to roots - and the herbicide follows.