Evaluating the effect of Row Spacing and Herbicide application on Weed Control in Direct-Seeded Rice

A field experiment was conducted to evaluating the performance of some post-emergence herbicides and different row spacing for weed control in direct-seeded rice at the Research Farm, Gorgan University of Agricultural Science and Natural Resources, in 2011. Treatments consisted of three crop spacing between the rows (15, 25, and 35 cm), and six chemical weed control (pendimethalin at 660 g a.i. ha-1, bentazon at 1200 g a.i. ha-1, propanil + cinosulfuron at 2160+20 g a.i. ha-1, oxadiargyl at 900 g a.i. ha-1, clodinafop propargyl + "bromoxynil + MCPA" + bentazon at 40+200+1200 g a.i. ha-1 and sethoxydim + "bromoxynil + MCPA" + bentazon at 250+200+1200 g a.i. ha-1). Weed-free treatment also was included in the experiment. The plots were divided into two sections, treatments were applied in a section and the other part of each plot was considered as the control of treated section. The pendimethalin was sprayed 7 days after sowing (DAS) and other experimental herbicide treatments were applied at 35 DAS. The dominant competitiveness weed species were Xanthium strumarium (L.), Sorghum halepense (L.) Pers., Abutilon theophrasti Medik., Amaranthus retroflexus (L.) and Echinochloa colona (L.). Effect of reduced row spacing on dry matters of weed was significant at 77 and 89 DAS. Dry matters of weeds with all the chemical weed control treatments at all stages were lower than those of their weedy checks. However, none of the herbicide treatments were as effective as the weed-free treatment in reducing the dry matter of weeds. The lowest reduction in total weed dry weight was recorded with oxadiargyl herbicide. Among the herbicides evaluated, sethoxydim + "bromoxynil + MCPA" + bentazon, propanil + cinosulfuron and clodinafop propargyl + "bromoxynil + MCPA" + bentazon perfomed well as they effectively controlled weeds comparable to the weedy checks.