| Off-target movement of glyphosate onto rice is a perennial concern when rice is grown in close proximity to glyphosate-tolernat crops. If differential tolerance to sub-lethal rates of glyphosate exists among rice (Oryza sativa) cultivars, these cultivars could be utilized in breeding programs or glyphosate-drift sensitive areas. Field and greenhouse experiments were conducted in 2006 and 2007 to examine differences among rice cultivars in response to sub-lethal rates of glyphosate, and to examine imidazolinone-tolerant rice response to imazethapyr and sub-lethal rates of glyphosate applied sequentially to determine the potential for either herbicide to predispose rice to greater injury. In the field experiment, glyphosate was applied at 0, 45, and 90 g ae/ha at the 3- to 4-leaf, panicle initiation, and boot growth stages of 10 rice cultivars. Cultivars inherently differed in plant height, flag leaf length, and yield. Glyphosate applied at the 3- to 4-leaf stage reduced plant height and yield of cultivars less than 5%. Height of all cultivars was affected more by glyphosate at 90 g/ha applied at panicle initiation, but the greatest yield reduction across all cultivars was from 90 g/ha glyphosate applied at boot stage. Relative flag leaf length of some cultivars was reduced by glyphosate more at one location than the other, and this reduction differed by growth stage. In field and greenhouse experiments, glyphosate was applied at 0, 45, and 90 g ae/ha at 14, 7, 3, 1, and 0 d prior to applications of imazethapyr at 0, 105, or 210 g ai/ha to the imidazolinone-tolerant cultivar 'CL 161'. Imazethapyr at those rates was also applied 14, 7, 3, 1, and 0 d prior to receiving glyphosate at the above rates to determine any predisposition of CL 161 to either herbicide. Glyphosate reduced relative plant height, relative dry mass, and relative yield of CL 161. There was no interaction between imazethapyr and glyphosate on relative plant height, relative dry mass, relative leaf chlorophyll content, or relative yield; therefore, influence is independent. There is no evidence that sequential applications of imazethapyr or sub-lethal rates of glyphosate will predispose CL 161 to greater injury from either herbicide. |
