Herbicidal Properties of 2-Methoxyethyl N-[3-Fluorobenzoyl]-N-[4-chloro-2-fluoro-5-(3-butyn-2-yloxy) phenyl]-3, 4, 5, 6-tetrahydrophthalamate (CUH-35) and Behavior in Paddy Soil

CUH-35, 2-methoxyethyl N-(3-fluorobenzoyl)-N-[4-chloro-2-fluoro-5-(3-butyn-2-yloxy) phenyl]-3, 4, 5, 6-tetrahydrophthalamate (Table 1), was studied for its herbicidal activity, selectivity and behavior mainly under flooded conditions. The results are summarized as follows: 1. Greenhouse trial 1-1. Weed spectrum and crop tolerance of CUH-35. CUH-35 showed a potent herbicidal activity toward Echinochloa oryzicola Vasing., Cyperus difformis L., Monochoria vaginalis Presl., Rotala indica Koehne., Lindernia procumbens Borbas., Scirpus juncoides Roxb., Eleocharis acicularis Roem., and Cyperus serotinus Rottb, at 25g a. i./ha by pre-emergence application under flooded conditions. It inhibited the growth of direct-seeded rice plants at a dose of 6.3g a. i./ha, while transplanted rice plants were not affected even at 100g a. i./ha (Table 3). 1-2. Application time CUH-35 completely inhibited the growth of Rotala indica at 50g a. i./ha when applied at pre-emergence at the 2-leaf stage. On the other hand, it also showed a strong herbicidal toward against Echinochloa oryzicola at pre-emergence, but not at the 2-leaf stage (Fig. 2). 1-3. Behavior in soils. After leakage treatment (3mm/hr), CUH-35 applied to the soil surface was found to remain within a depth of 0-1cm in both clay loam and loam soils. In the case of sandy loam soil, the herbicide leached down to a 2cm depth (Table 4). CUH-35 applied at 100g a. i./ha completely inhibited the growth of Echinochloa oryzicola seeded at 35 days after treatment (Fig. 4). 2. Field trial. CUH-35 effectively controlled major annual paddy weeds without causing any injury to transplanted rice when applied immediately after or 7 days after transplanting at a dose as low as 100g a. i./ha. Herbicidal efficacy of CUH-35 toward weed species in the field trial was very similar to that in the greenhouse tests, and was not appreciably affected by the seed depth of weeds. On the other hand, the herbicidal activity was lower in the field trial than in the greenhouse tests, indicating that the degradation and downward movement of CUH-35 resulted in the dilution of the concentration in the soil surface during the period of weed emergence, As a result, the pre-emergence activity may have been lost, leading to a 2nd flush of weeds.