Herbicidal properties of bromobutide, a new herbicide: Herbicidal efficacy and injurious effect on rice

In order to analyse the properties of bromobutide [(R, S)-2-bromo-N-(α, α-dimethylbenzyl)-3, 3-dimethylbutyramide] as a paddy field herbicide, efficacy against paddy weeds and injurious effect on rice were investigated under greenhouse and outdoor conditions. The results obtained are summarized as follows. 1. Bromobutide did not inhibit the germination of weeds, but strongly inhibited the growth of weeds after emergence. Bromobutide applied at the post-emergence stage of weeds also strongly inhibited the growth of foliar and underground parts of weeds such as Sagittaria pygmaea Miq. and Cyperus serotinus Rottb. (Fig. 2 and 3). 2. Under greenhouse conditions, bromobutide applied at the pre-emergence or very early post-emergence stages of weeds, at doses of less than 20g/a, controlled effectively annual weeds such as Echinochloa oryzicola Vasing., Monochoria vaginalis (Burm. f.) Presl, Lindernia pyxidaria L., Rotala indica (Willd.) Koehne and perennial weeds such as Scirpus juncoides Roxb. subsp. juncoides Roxb., Eleocharis acicularis (L.) Roem. et Schult. var. longiseta Sven., C. serotinus, Eleocharis kuroguwai Ohwi and S. pygmaea. Bromobutide was especially effective against S. juncoides, and it controlled the weed even at doses as low as 1.25g/a (Table 1). 3. Based on the results of tests using concrete pots placed outdoors for the evaluation of the practical performance of bromobutide, 6% granules of bromobutide at doses of 12-24 a. i. g/a controlled effectively Cyperaceae weeds such as S. juncoides and C. serotinus. However the effect against E. oryzicola and S. pygmaea varied with the doses or time of application, and the effect against broadleaved-weeds was not satisfactory. Granular combinations of bromobutide+chlomethoxynil, 6+5% and bromobutide+bifenox, 6+5% controlled effectively all the weeds examined (Table 2). 4. Possible injury of bromobutide to transplanted rice was examined using 1/5, 000 a Wagner pots. Though bromobutide slightly inhibited the growth of young rice seedlings when applied at relatively high doses of 36g/a, it did not display any injurious effect when applied at lower doses or when the leaf stage of the rice seedlings exceeded 3.5 (Table 3).