Abstract: Studies were conducted in 1997 and 1998 at the Northeast Mississippi Research and Extension Center to investigate the effects of row spacing (76, 38, and 19 cm), soybean population, and three weed management systems on sicklepod growth and seed production. The cultivars ‘Hartz 5088RR’ (glyphosate-tolerant) and ‘Hutcheson’ (a conventional cultivar) were used in two separate studies. The average soybean populations over cultivars and year were 245,000 (low), 481,000 (medium), and 676,000 (high) plants/ha. The three weed management systems were: no (untreated), one, and two herbicide applications. In the glyphosate-tolerant system, one or two postemergence (POST) applications of glyphosate were used, whereas in the conventional system, flumetsulam plus metolachlor preemergence was used alone (single) or followed by chlorimuron POST (sequential). Reducing soybean row spacing from 76 cm, coupled with increased soybean population, reduced sicklepod population up to 80%. Except for Hutcheson in 1998, reducing row spacing and increasing soybean population also reduced sicklepod seed production in both the untreated and the single applications. A single herbicide application reduced sicklepod population up to 68% from untreated plots. However, except for Hartz 5088RR in 1998, the sequential application did not further reduce sicklepod population. In a shading study, partial shading increased sicklepod height but reduced dry weight. However, as shading level increased from 65 to 80 and 95%, height was also reduced.
Nomenclature: Chlorimuron; flumetsulam; glyphosate; metolachlor; sicklepod, Senna obtusifolia (L.) Irwin and Barnaby #3 CASOB; soybean, Glycine max (L.) Merr.
Additional index words: Glyphosate-tolerant soybean, sequential herbicide applications, seed production.
Abbreviations: MG, maturity group; POST, postemergence; PRE, preemergence; WAP, weeks after planting.
