Herbicidal and phytotoxic properties of pyributicarb, a new paddy herbicide, and its movement in soil [of rice Oryza sativa field]

The herbicidal activity of pyributicarb, O-3-tert-butylphenyl 6-methoxy-2-pyridyl (methyl)-thiocarbamate (Fig. 1; I), was evaluated in a green house for use as a new paddy herbicide and the results were as follows: 1) Pyributicarb showed an outstanding herbicidal activity against Echinochloa oryzicola Vasing., Cyperus difformis L., Monochoria vaginalis (Burm. f.) Presl var. etc. at the dosage of 0.75-1.5g a. i./a by pre-emergence application under flooded conditions. The herbicide could also control Scirpus juncoides Roxb. and Cyperus serotinus Rottb. at the dosage of 6g a. i./a. The herbicide showed almost no activity against Sagittaria pygmaea Miq. at the dosage of 100g a. i./ a. On the other hand, pyributicarb did not exhibit any phytotoxicity to young transplanted rice seedlings (Oryza sativa L. cv. Nipponbare; two-leaf stage) at all even at the dosage of 100g a. i./a (Fig. 2). Thus, the herbicide showed a good selectivity between transplanted rice plant and annual paddy weeds. 2) Pyributicarb effectively controlled E. oryzicola from pre-emergence to the two-leaf stage at the dosage of 2.5g a. i./a (Fig. 3). Although the herbicide showed a high activity against S. juncoides at the dosage of 10g a. i./a by application at the 0-0.2-leaf stage, no activity was observed against the weed at the 1.2-leaf stage (Fig. 4). 3) Pyributicarb showed a high herbicidal activity against E. oryzicola which was seeded at a depth of 0-2cm under the soil surface at the dosage of 1.25g a. i./a (Fig. 5). Although the herbicide could control S. juncoides seeded on the soil surface, no activity was observed against the weed seeded at a depth of 0.5-1cm under the soil surface (Fig. 6). 4) Pyributicarb did not injure transplanted rice plants at the two-leaf stage at the dosage of 80g a. i./a even if the transplanting depth of the rice seedlings was only 1cm under the soil surface. When the transplanting depth was 0cm, namely all the roots of the rice seedlings were settled on the soil surface, phytotoxicity of the herbicide to rice plants was observed, but the herbicide could not kill the plants completely (Fig. 7). 5) Mobility of pyributicarb in Shin-nanyo soil (clay loam) was determined by a bioassay using a soil column. The movement of pyributicarb in the soil seemed to be very limited. It was assumed that most of the pyributicarb applied remained in the 0-1cm layer under the soil surface (Fig. 8).