Absorption of naproanilide by several plants and effects of other herbicides on its absorption

The absorption of the herbicide naproanilide 2-(2-naphthoxy) propioanilide, and the distribution of its phytotoxic metabolite 2-(2-naphthoxy) propionic acid (NOP) were investigated in rice plants (Oryza sativa L., a tolerant species) and in Sagittaria pygmaea Miq., Scirpus juncoides Roxb., Cyperus difformis L. and Monocholia vaginalis Burm. f. (susceptible species). Naproanilide was metabolized rapidly to phytotoxic NOP in all of the plant species tested. The concentrations of naproanilide and NOP greatly differed among plants, all of the susceptible plants showing much higher concentrations than the tolerant rice plants from the 1st day after treatment to the 7th day. In S. pygmaea the concentration of NOP in tubers increased linearly with time, whereas that in shoots reached a maximum at the 3rd day, and decreased thereafter. Little NOP was contained in roots compared with the shoots and tubers. Naproanilide and/or NOP absorbed in the shoots moved basipetally in S. pygmaea. When naproanilide and butachlor were applied in combination, the concentration of NOP in S. pygmaea was 1.4 to 2.6 times higher than that with naproanilide alone or in conbination with benthiocarb.