Abstract
A field experiment was conducted in 1993-94 to study the effect of five post-emergence herbicide combinations on weed control and yield of wet seeded (WS) and transplanted (TP) main rice (Oryza sativa L.) crop (MC) and its ratoon (RC). Common weeds which occurred in this study were Fimbristylis littoralis Gaudich, lschaemum rogusum Salisb., Sphenoclea zeylanica Geartn., and Ludwigia hyssopifolia (G. Don) Excell. Combinations of propanil (3.0 kg a.i. ha-1) with oxadiazon (3.0 kg a.i. ha·1), pendimenthalin (1.5 kg a.i. ha·1), and butachlor (2.0 kg a.i. ha·1) were applied 14 days after seeding (DAS) and 7 days after transplanting (DAT) and a split application of propanil (3.0 kg a.i. ha-1 + 3.0 kg a.i. ha-1) was applied 14 DAS, 28 DAT, and 7 DAT. The 21 DAT treatment resulted in lower weed biomass and better crop yields than propanil plus 2,4-D (3.0 kg a.i. ha-1 + 0.5 kg a.i. ha-1) applied 14 DAS and 7 DAT. Higher weed biomass was associated with WS in the MC (78 g m-2) and TP in the RC (184 g m-2). The MC and RC grain yields were similar in both planting systems under optimum weed control. Weeds that emerged in the RC differed from those of the MC, but herbicides producing good weed control in the MC resulted in better control in the RC, especially under WS.
