ホタルイ類水田雑草の防除に関する生理生態学的研究

Abstract

The author studied the physiological and ecological characteristics of Scirpus weeds, so-called “hotarui”, Scirpus juncoides Roxb. var. hotarui Ohwi, S. juncoides Roxb. var. ohwianus T. Koyama and S. wallichii Nees, then identified the dominant species of Scirpus weeds in paddy fields and determined the cause of the dominance of the species. Based on these data, the author attempted to establish an effective control method for this noxious weed.1. The numbers of chromosomes in the pollen mother cells of S. juncoides var. hotarui, S. juncoides var. ohwianus and S. wallichii were 22, 37 and 36 respectively.Although S. juncoides var. ohwianus was identified in all the seed samples collected from 17 research stations in 15 prefectures, S. juncoides var. hotarui was not detected at all. S. wallichii and S. hondoensis Ohwi var. leiocarpus Ohwi was identified in 3 and 1 seed samples respectively at very low rates.Scirpus plants S. juncoides var. hotarui were never observed in paddy fields where almost all Scirpus plants consisted of S. juncoides var. ohwianus and a few rest was S. wallichii.2. Seeds of the three species which overwintered under submerged conditions showed higher emergence rates than those in soils under damp and upland conditions in a greenhouse.The temperatures at which S. juncoides var. hotarui, S. juncoides var. ohwianus and S. wallichii emerged were in the range of 25-35°C, 15-35°C and 20-40°C, respectively.The emergence rates of S. juncoides var. hotarui and S. wallichii were reduced by covering with soil at depths of more than 1 and 1.5cm respectively, but those of S. juncoides var. ohwianus were not reduced by covering with soil at a depth of 3cm.S. juncoides var. hotarui and S. juncoides var. ohwianus sown in soils containing more than 75% of water in MWC base showed more than 70% emergence, but S. wallichii gave 94% emergence in soil containing 40% of water in MWC.3. When the seeds were sown in turn from April 12th to July 17th, the growth of S. juncoides var. ohwianus was faster than that of the other two species at any time.The growth of the three species was delayed almost linearly with the increase in shade intensity. But the decrease in the stem number of S. juncoides var. ohwianus with shading was less pronounced than that of the other two species under shaded conditions, compared with the control.4. Under natural day length conditions, the time of heading and flowering of S. juncoides var. hotarui was the most delayed.The heading of S. juncoides var. hotarui and S. wallichii was remarkably delayed or inhibited by shading whereas that of S. juncoides var. ohwianus was also delayed but to a lesser extent than that of the other two species.The three species cultivated under natural conditions regrew after their aerial parts were cut off on the 25th of October. Although 50% of the regrown plants of S. juncoides var. ohwianus headed, none of the other species did.The mean numbers of seeds per stem of S. juncoides var. hotarui, S. juncoides var. ohwianus and S. wallichii were 93, 317 and 267 respectively.5. S. juncoides var. hotarui, S. juncoides var. ohwianus and S. wallichii overwintered regardless of soil moisture content.When the weights of overwintering stumps of S. juncoides var. hotarui and S. juncoides var. ohwianus were reduced to less than 32% of the initial weight by drying