A survey of the growth and development of Echinochloa spp. in paddy fields and its effects on rice plants.
Echinochloa crus-galli var. crus-pavonis and E. crus-galli are the main grasses in paddy fields in Jiashan County, Zhejiang Province. The population of the grasses in seedbeds was 31 500 for the 2nd rice crop, 11 500-23 600 for the 1st rice crop and 9500 for the late rice crop. Echinochloa spp. in the paddy fields included volunteers and individuals transplanted in hills. In the 1st rice crop there were 788-10 417 volunteers and 407-1191 transplanted plants/mu, but in the 2nd rice crop there were only 433-3126 transplanted plants/mu. Echinochloa spp. grew faster than rice, competing for light and nutrients and decreasing the rice yield. In the 2nd rice crop with a hill of rice formed by 4 plants 1 of which was E. crus-galli with 3-4 leaves or with 6 leaves, the panicle number/hill, the number of fully filled grains/panicle and 1000-seed weight were 5.1, 32.4 and 22.3 and 3.9, 29.4 and 20, resp.; the corresponding data for a hill without an E. crus-galli plant were 9.2, 39.7 and 24.1. The emergence of E. crus-galli seeds sown 1, 2 and 3 cm deep was 26, 13 and 5%, resp. There was a tendency for the panicle length, seed number/panicle, rate of maturity and shattering percentage of E. crus-galli to decrease with delay in transplanting the 2nd rice crop. The high shattering of Echinochloa spp. seeds is the principal source of the grasses in seedbeds and of volunteer plants. [1 mu = 0.067 ha].