I guess I don't understand its use, standalone, in ag crops unless there are broadleaf weeds it controls better than some of the other broadleaf herbicides. MCPA or its cousin, MCPP are most often mixed with 2,4-d and dicambia. The mixtures control and kill broadleaf weeds in combination better than each herbicide alone. I see those sorts of combinations used mostly post emergent on turf or in small grains. I looked at a few labels and all had the MCPA tank mixed with some other herbicide determined by the crop and the weeds needing controlled. It does persist in he soil and the half life is dependent on the soil organic matter content. Even so, and this is just my opinion, after 15 - 18 days most of it's effect is minimized. Again, just my opinion, I think you'd be better off using your MCPP in combination with something else. See above....
From Wikipedia
Commercial use[edit]
MCPA is used as an herbicide, generally as its salt or esterified forms. Used thus, it controls broadleaf
weeds, including
thistle and
dock, in cereal crops and
pasture. It is selective for plants with broad leaves, and this includes most
deciduous trees.
Clovers are tolerant at moderate application levels. It is currently classified as a
restricted use pesticide in the
United States. Its toxicity and biodegradation are topics of current research. One formulation is described by its manufacturer as "designed for specific markets that require the safest possible phenoxy product, primarily for use in the Pacific Northwest".
[5] Though not extremely toxic,
[6] it has recently been determined that MCPA can form complexes with metal ions and thereby increase their bioavailability,
[7] though there is also work being done to utilize this ability.
[8]