Abstract
The leaf stage and duration of emergence of Echinochloa oryzicola Vasing. were investigated in relation to the soil temperature of paddy fields in cool, temperate regions of Japan. For the period from the puddling day to each leaf stage (DL), 1/DL exhibited a high positive correlation with the average soil temperature (TA). For the period from the puddling day to the termination of emergence (DE), 1/DE exhibited a high positive correlation with the average of daily maximum soil temperature (TM). The following regression equations were obtained from these relationships: 1/DL=aTA+b (where a is a coefficient and b is a constant) and log(1/DE)=aTM+b. These equations can be used to estimate leaf stage and duration of emergence in E. oryzicola. Moreover, the value DE-DL can be used to estimate the required period for the residual effect of herbicides on the emergence pattern of E. oryzicola. The equations obtained in this report should be useful for optimizing herbicide treatment in cool, temperate regions of Japan.
