Identification of Paddy-field Scirpus Weeds, So-called “Hotarui”

IWASAKI Keizo, WATAJIMA Tomoji, HAGIMOTO Hiroshi

doi:10.3719/weed.25.110

The present authors tried to make clear a dominant species of Scirpus weeds or so-called “hotarui” in Japanese paddy rice fields. 1. Although Scirpus juncoides Roxb. var. ohwianus T. Koyama was identified in all the seed samples sent from 17 research stations in 15 prefectures, S. juncoides Roxb. var. hotarui Ohwi was not at all. S. wallichii Nees appeared from 3 seed samples. S. wallichii was also sent from Akita Prefectural Agricultural Experiment Station where this species had been separated from S. juncoides var. ohwianus. S. hondoensis Ohwi var. leiocarpus Ohwi appeared from only Hokkaido Agricultural Experiment Station. But their percentages were very low, that is, S. wallichii and S. hondoensis var. leiocarpus appeared 1-3 and 9% respectively. 2. Eleven kinds of herbicides showed excellent effects on S. juncoides var. hotarui by both pre- and post-emergence applications. By the pre-emergence application ethyl ester of MCPA, sodium salt of PCP, butachlor, benthiocarb and piperophos showed also high effects on S. juncoides var. ohwianus and S. wallichii, but only ethyl ester of MCPA and bentazon showed high effects on the above 2 species by the post-emergence application. Trifluralin had no effect on the 3 kinds of Scirpus, and both simetryne and dimethametryn had no effects on S. wallichii. 3. In consequence of our investigations on the growing place of Scirpus plants on the outskirts of Fukuchiyama city, adult plants of S. juncoides var. hotarui were recognized at only 4 non-cropping paddy fields, a balk and footpath and a non-rice transplanted area in a paddy rice field. It was growing together with short plants in swampy places. But it was never observed in rice-growing paddy field, where almost all Scirpus plants were S. juncoides var. ohwianus. 4. The noxious “hotarui” in Japanese paddy rice fields must be S. juncoides var. ohwianus.

Identification of Paddy-field <i>Scirpus</i> Weeds, So-called “Hotarui”

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