Effect of water overflowing from a herbicide‐treated rice field on herbicide performance

Water overflowing from plots 2h after applying butachlor at rates ranging from 0.3 to 1.0 kg ai/ha did not decrease weed control of treated plots and grain yield were significantly higher than those of untreated check plots. Yields in plots that received butachlor directly, or by overflowing into similar sized receiving plots did not differ significantly from those in plots treated with butachlor where no overflowing occurred. Doubling or tripling the size of the untreated plots that received butachlor from a treated plot resulted in poor weed control and lower grain yields. Similar results were obtained when butachlor was applied as an EC or as a granule to the treated plots. The weed control obtained in untreated plots receiving overflow water from butachlor‐treated plots resulted from considerable amounts of the applied herbicide remaining suspended in floodwater for 1h after overflowing (3h after application). The performance of pretilachlor‐fenclorim, bensulfuron, butachlor‐2,4‐D, piperophos‐2,4‐D, and thiobencarb with or without 2,4‐D was also not affected by water overflowing from herbicide‐treated fields 2h after soil application.