Main content area

Hemp sesbania interference in drill-seeded glyphosate-resistant soybean

Norsworthy, Jason K., Oliver, Lawrence R.
Weed science 2002 v.50 no.1 pp. 34-41
Glycine max, Sesbania exaltata, buried seeds, developmental stages, field experimentation, glyphosate, hemp, herbicide resistance, planting, seed yield, sowing, soybeans, weed control, weeds, Arkansas
Field experiments were conducted at Fayetteville, AR, in 1997, 1998, and 1999 to evaluate the degree of interspecific interference between drill-seeded, glyphosate-resistant soybean and hemp sesbania as influenced by soybean population, hemp sesbania density, and a single glyphosate application. Soybean was planted at 247,000, 430,000, and 618,000 seed ha⁻⁻¹ with early-season emergence of 217,000, 371,000, and 521,000 plants ha⁻⁻¹. Hemp sesbania densities were 0, 4, 10, and 16 plants m⁻⁻² in combination with 0 and 1.12 kg ai ha⁻⁻¹ glyphosate applied at the V4 to V6 soybean growth stage. Untreated hemp sesbania produced a maximum of 49 million seed ha⁻⁻¹ with 217,000 soybean ha⁻⁻¹, whereas seed production of glyphosate-treated hemp sesbania ranged from 2.8 to 0.6 million seed ha⁻⁻¹ with 217,000 and 521,000 soybean ha⁻⁻¹, respectively. Soybean seed yield was reduced 43%% by 16 untreated hemp sesbania m⁻⁻², while glyphosate-treated hemp sesbania did not reduce seed yield. Averaged over all untreated hemp sesbania densities, soybean yield loss was reduced from 44 to 22%% by increasing the soybean population from 217,000 to 521,000 plants ha⁻⁻¹. Because of the absence of soybean yield loss at 521,000 soybean ha⁻⁻¹, this density appears beneficial when using a single application of glyphosate to provide season-long weed control. However, a single glyphosate application in combination with a high soybean density did not completely prevent hemp sesbania seed production, and the seeding rate required to achieve a stand of 521,000 plants ha⁻⁻¹ would not be affordable; thus, alternate management methods targeting hemp sesbania must be employed to prevent an increase in the number of seed in the soil seedbank and to prevent a potential shift in the weed spectrum.Nomenclature: Glyphosate; hemp sesbania, Sesbania exaltata (Raf.) Rydb. ex A.W.Hill SEBEX; soybean, Glycine max L.