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Many herbicides target the hormone: Auxin
Auxin plays a major role in controlling cell elongation during photo- and gravitropism. Control of cell elongation is just one of many auxin responses. Auxin is a term that refers to compounds that, when applied to plants of plant tissues, cause growth effects that are similar to those seen with indoleacetic acid. Auxins include compounds like 2,4-D and NAA (2,4-D IS A COMMON HERBICIDE and NAA is often included in mixtures used to stimulate root formation in cutting). So, it is not hard to fathom that 2,4-D is a player in this problem.´╗┐