Seed production and seedling emergence of three broadleaf weed species were evaluated following glyphosate application at initial seed set, mid seed fill, and physiological maturity. In greenhouse experiments averaged across glyphosate rates of 0.42, 0.63, and 0.84 kg ae ha−1, Xanthium strumarium 100-bur weight and burs per plant were reduced at least 69 and 70%, respectively, for application at initial fruit set compared with later applications, and seedling emergence was 3% of the nontreated check. Glyphosate application at initial seed set reduced Sesbania exaltata 100-seed weight 73%, seed per plant 86%, and seedling emergence 94%. Senna obtusifolia 100-seed weight, seed per plant, and seedling emergence were reduced 46, 83, and 66%, respectively, when glyphosate was applied at initial seed set. In field experiments, X. strumarium and S. exaltata seed production were reduced only when glyphosate was applied at initial seed set. Compared with the nontreated check, seedling emergence following initial seed set application was reduced 82% for X. strumarium and 94% for S. exaltata. S. obtusifolia response in the field was inconsistent with no reductions in seed per plant or seedling emergence observed the first year. The second year, initial seed set application reduced seed per plant 88% and seedling emergence 72%.
Nomenclature: Glyphosate; Xanthium strumarium L. XANST, common cocklebur; Sesbania exaltata (Raf.) Rybd. ex A. W. Hill SEBEX, hemp sesbania; Senna obtusifolia L. CASOB, sicklepod.