Auxins are a class of plant hormones (or plant growth regulators) derived from tryptophan. Auxins are found in the tips of shoots and roots and promote cell division, stem and root growth. They can also have a radical effect on plant orientation by promoting cell division on one side of the plant in response to sunlight and gravity, called phototropism. 

Auxinic herbicides are organic compounds that are used as active ingredients in many herbicide preparations. These are the oldest synthetic herbicides.

There are five groups of auxinic herbicides, including benzoic acid derivatives such as dicamba, chlorambene, 2,3,6-TBA, etc.

Used as plant growth regulator, 4-CPA is absorbed by plant via root, stem, leaf, bloom and fruit, It is used to prevent abscission of bloom and fruit, inhibit rooting of beans, promote fruit set, induce ormation of seedless fruit. Also used for ripening and fruit thinning. It performs better when used in combination with 0.1% monopotassium phosphate. It also has herbicidal effect at high dosage.