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.

Picloram is a systemic herbicide used for general woody plant control. It also controls a wide range of broad-leaved weeds, but most grasses are resistant. A chlorinated derivative of picolinic acid, picloram is in the pyridine family of herbicides.

Picloram can be sprayed on foliage, injected into plants, applied to cut surfaces, or placed at the base of the plant where it will leach to the roots. Once absorbed by the foliage, stem, or roots, picloram is transported throughout the plant.