Terbuthylazine is a selective herbicide. Chemically, it is a halogenated triazine; compared with atrazine (1958 inv., Geigy lab) and simazine, it has a tert-butyl group in place of the isopropyl and ethyl group, respectively. The sim-azine molecule with 2 ethyl groups is symmetric and flat (excepting its equal ends). The threefold substituted triazines have resonance of the free (non-bonding, -) electron pairs, resulting in equivalent mesomeric structures.
Simazine remains active in the soil for 2 to 7 months or longer after application. Atrazine remains in soil for a matter of months (although in some soils can persist to at least 4 years) and can migrate from soil to groundwater.
Terbuthylazine's HRAC classification is (global, Aus), (numeric), as it inhibits photosynthesis at photosystem II.