水田多年生雑草の繁殖特性の解明と防除に関する研究

Abstract

The present studies have been undertaken to obtain basic information on the ecological characteristics of propagules and factors affecting their formation and death. Such information is necessary for the control of perennial weeds whose incidence has increased in various areas in recent years. The experiments were conducted at the Central Agricultural Experimental Station in Konosu, Saitama, during the period 1971-1980.1. Based on the ecological characteristics of propagules of perennial weeds in paddy fields the weeds were classified into three types as follows; non-clonal growth type, rhizome type and prostrated type according to the growth pattern of the above-and underground organs.Weeds belonging to the non-clonal growth type were found to produce many seeds and propagation through seeds was easy. Scirpus juncoides, Alisma canaliculatum and Sagittaria trifolia (arrow head) belong to this type. Among them, the former two species propagate through seeds in paddy fields. Rhizome type weeds propagate with propagules such as tubers and rhizomes. Cyperus serotinus (cyperus), Eleocharis kuroguwai (water chestnut) and Sagittaria pygmaea (pygmaea arrowhead) belong to this type. Weeds of this type propagate actively and cause serious damage to rice plants. In the prostrated type weeds, runner or rhizomes grow rapidly underground at a comparatively shallow depth and regenerate easily even when runners or rhizomes are cut in short pieces. Paspalum distichum and Oenanthe javanica belong to this type.2. Length of dormancy period of propagules, uniformity of awakening from dormancy and requirement of oxygen for germination are internal factors that affect the generation of weeds. In addition the morphology and function of propagules were found to be closely related with the emergence and propagation of weeds.3. As for the propagule formation, pygmaea arrowhead is a plant insensitive to photo period which produces tubers 50 to 60 days after emergence even if the date of emergence varies.As for the propagule formation of cyperus, water chestnut, arrowhead and Potamogeton distinctus (pond weed), these are short-day plants which produce propagules in the fall although the sensitivity to short-day varies among the species. Heading and flowering are controlled by short-day in cyperus and water chestnut as well as tuber formation, while in the other three species the response to tuber formation is not controlled by short-day.4. The formation of propagules varies depending on the temperature and soil moisture as well as on daylength. The propagule formation in all of the above mentioned five species, was inhibited by high temperature. Especially in the case of the pond weed, a temperature higher than 30°C inhibited winter bud formation almost completely.When the density of rice plants is high, the emergence of perennial weeds with broad leaves such as arrow head and pond weed is markedly suppressed due to shading. As a result no propagule formation was observed after a period of three years.5. Location of propagules in soil is different in each weed. It is shallowest for pygmaea arrowhead and cyperus in which most of the propagules are produced at depths ranging between 5 and 10cm. On the other hand, pond weed produces propagules in a deeper zone immediately above the subsoil. Water chestnut and arrow head show a characteristic vertical distribution of propagules.6. Propagules of pygmaea arrowhead, cyperus and water chestnut died when their moisture content decreased to 40%, whereas those of the pond weed were much more resistant to desiccation. On the other hand, the lowest temperature lethal to propagules ranged between -5°C and -7°C, being lowest in cyperus and highest in pygmaea arrowhead.7. As for weed control, use of herbicides and control through cultural practices were investigated.