Competition of Barnyardgrass with Rice Varieties

A field study was conducted to examine the competition of barnyardgrass with various rice varieties and its effect on propanil effectiveness. Six rice varieties, Ispaniki A', Strymonas and Roxani (Japonica type) and Rea, Skybonnet and Blue belle (Indica type), were grown in a silty loam soil, in 1994 and 1995. The varieties had different 1000 seed weights, which varied from 24 to 40 g. The herbicide propanil was applied at the four-leaf stage of barnyardgrass on half the plot area. Japonica type varieties emerged earlier and had lower numbers of barnyardgrass plants compared to Indica varieties. The time of seedling emergence was significantly and negatively correlated with the seed weight and positively with the number of barnyardgrass plants. The delayed establishment of Indica type varieties favoured rapid barnyardgrass growth at the early stages and resulted in lower effectiveness of propanil, compared to Japonica type varieties. Thus, in controlling barnyardgrass in rice fields it is necessary to take into account the variety grown in order to reduce production costs and the pollution risk to the environment.