Abstract
In order to establish efficient methods of control of the arrowhead weed (Sagittaria trifolia L.) in paddy fields in Japan, the longevity of the weed tubers in paddy fields was examined from 1981 to 1983, as the longevity of the tubers in paddy soil had not been studied. Seasonal changes of the tubers which survived in the paddy fields were studied from 1982 to 1983. Effect of drying or cutting on the longevity of the tubers was also analysed in relation to the effect of rotary tillage.
The results obtained were as follow;
(1) The tubers were distributed in the soil from the surface layer to the layer under the plow sole. The tubers in the surface layer were smaller in size, and those in the layer under the plow sole were larger.
(2) The larger tubers tended exhibit a deeper dormancy than the smaller ones as determined by incubation with immersion in water at 25 or 30°C and under on illumination of at 5, 000lx (24 hours). However, after rice transplanting, the dormancy of the majority of the tubers was broken.
(3) About more than half of the tubers in the soil were injured by rotary tillage in the spring, and among the tubers which divided, only those in which the growing points of the terminal buds were included were able to sprout. The tubers were not injured by puddling.
(4) The living tubers gradually disappeared from the soil subjected to repeated rotary tillage in the spring and by emergence of the weed during the rice growing season. The number of tubers rapidly decreased after midseason drainage, and few tubers were observed at harvest in the autumn following the formation of tubers.
(5) The tubers died due to drying after being placed on the soil surface for six days and after about eight weeks when placed in non-irrigated soil at a depth of five centimeters under glasshouse conditions. This suggested that only a few tubers would therefore be killed in the field even if they were distributed at the surface of the soil through tillage.
(6) The results obtained suggest that the propagation of the tubers of the arrowhead weed in the following year is negligible since tuber formation would not be able to occur in the season, because the longevity of the tubers is less than one year.
