Abstract
The efficacy of glyphosate [N-(phosphonomethyl) glycine] as post-directed (shielded) treatment in combination with preemergence metribuzin was evaluated in two experiments conducted at the Lajas Substation in 1984-85 and 1985-86. Glyphosate at 0.41, 0.84 and 1.64% on v/v basis did not cause phytotoxicity to pigeon pea in 1984-85. A very low toxicity (1.25%) occurred in 1985-86. Weed control by preemergence metribuzin (0.62 kg ai/ha) plus two post-directed applications of glyphosate ranged from good (79%) to excellent (97%) at 7 weeks after planting and 95 to 100% of control after 11 weeks in 1984-85. In 1985-86 weed control by this herbicide sequence was similar to that of 1984-85 both at 7 and 17 weeks after planting. Excellent pod yields were obtained with metribuzin plus glyphosate treatments in 1984-85. The highest yield (7,806 kg/ha) was obtained with metribuzin at 0.62 kg ai/ha plus glyphosate at 1.64% treatment. This yield exceeded significantly only that of the metribuzin alone treatment (6,363 kg/ha). There were no significant differences in yield among treatments in 1985-86. Pigeon pea yield ranged from 4,123 kg/ha in the metribuzin alone treatment to 6,170 kg/ha with metribuzin at 0.62 kg ai/ha plus glyphosate at 1.64% concentration.