Leaching of Bromacil and Norflurazon as Affected by Herbicide Mixture

It is a common practice to apply herbicides as mixtures of two or more products; however, no information is available about the effect of the mixture on leaching of each herbicide in soils. This study was designed to evaluate the effect of tank mixed herbicide combinations on the leaching potential of bromacil (5‐Bromo‐3‐sec‐butyl‐6‐methyluracil) and norflurazon [4‐chloro‐5‐(methylamino)‐2‐(a,a,a‐trifluoro‐m‐tolyl)‐3(2H)‐pyridazinone]. Leaching bromacil or norflurazon in soil columns under different increments of water application was measured using a radioactive tracer method. Metolachlor [2‐chloro‐ N ‐(2‐ethyl‐6‐methylphenyl)‐ N ‐(2‐methoxy‐1‐methylethyl)acetamide] and terbacil (3‐tert‐Butyl‐5‐chloro‐6‐methyluracil) significantly decreased the leaching of norflurazon when the amount of water application was equivalent to two or more pore volumes. Oxadiazon [2‐tert‐butyl‐4‐(2,4‐dichloro‐5‐isopropoxyphenyl)‐Δ 2 ‐1,3,4‐oxadiazolin‐5‐one] and simazine [2‐chloro‐4,6‐bis(ethylamino)‐ s ‐triazine] significantly reduced the leaching of norflurazon when three and four pore volumes of water were applied. Trifluralin (α,α,α‐Trifluoro‐2,6‐dinitro‐N,N‐dipropyl‐p‐toluidine) significantly decreased the leaching of norflurazon when two or three pore volumes of water were applied. The combining herbicides with bromacil had no effect on bromacil leaching except for diuron 4L formulation and napropamide, which decreased bromacil leaching under certain levels of water application. None of the herbicides tested significantly increased the leaching of bromacil or norflurazon.