Dr. Jones was working with the naturally occurring plant auxin, indole acetic acid (IAA). IAA is present in all plant matter and humans consume it daily whenever we eat fruit, vegetables and cereals. In an effort to work with a more chemically stable, auxin-like compound, Dr. Jones included 2,4-D, an analog of IAA, in his experiments and discovered that monocots (e.g. grasses) were left unharmed when sprayed with 2,4-D while growth was suppressed in dicots (e.g. broadleaf plants).
2,4-D plays an important role in protecting crops, improving agricultural yields, reducing the risk of invasive and poisonous species, protecting wildlife habitats, and protecting infrastructure. While improving food production and reducing food costs are what 2,4-D is best known for, environmental benefits include decreased soil erosion and decreased greenhouse gases through reduced soil tillage.