Dry-seeded rice systems are an emerging production technology in many Asian countries. A field study was conducted in 2011 and 2012 at the farm of the Rice Research and Development Institute, Batalagoda, Sri Lanka, to evaluate the performance of different herbicides in a dry-seeded rice system. Weed control treatments were nontreated (weedy), pretilachlor plus pyribenzoxim, cyhalofop-butyl, thiobencarb plus propanil, propanil, and bispyribac-sodium plus metamifop. All these POST herbicides were applied at 8 d after sowing, followed by an MCPA spray at 20 d after sowing. The dominant weeds in the study were barnyardgrass, Chinese sprangletop, and knotgrass. All herbicide treatments provided similar weed control, which ranged from 82 to 99%. Weeds in the nontreated plots reduced rice grain yield by 58 to 79% compared with the herbicide-treated plots. All herbicide-treated plots, except cyhalofop-butyl-treated ones, produced similar grain yield, which ranged from 3.7 to 4.2 t ha−1 in 2011 and from 6.0 to 7.0 t ha−1 in 2012. The results of our study suggest that different herbicides provided similar weed control and therefore different herbicides can be rotated in different seasons to reduce selection pressure on weeds.

Spatial patterns of the exotic riverine knotgrass (Paspalum distichum L.) were examined in Mediterranean river basins in Southwestern Iberia. The major goals of this study were to assess the degree of invasibility of riparian habitats by this species and to determine the influence of environmental factors and human-induced disturbances that this knotgrass has on both the landscape and the habitat scales. The present study demonstrates the ability of knotgrass to invade riparian habitats in Portuguese freshwater ecosystems. However, most of the spatial variation of the knotgrass cover seemed to be driven by local factors, such as fine sediment enrichment and the fragmentation of riparian woods, and by other anthropogenic interferences in relation to both the fluvial system and the surrounding landscape.