Effect of Imazaquin and Chlorimuron Plus Metribuzin on Sicklepod (Cassia obtusifolia) Seed Production and Germination

Abstract

Sicklepod seed production and germination were evaluated in density and weed-free period studies without herbicide treatment and after imazaquin or metribuzin plus chlorimuron were applied PRE in soybean. Neither herbicide nor sicklepod density affected sicklepod seed germination, but delaying emergence of sicklepod from 0 wk to 8 wk after soybean emergence reduced subsequent sicklepod seed germination from 92% to 48%. Increasing sicklepod density from two to eight plants per row m reduced sicklepod seeds per plant, but increased sicklepod seeds per m2, regardless of herbicide. Extending the weed-free period from 0 to 8 wk reduced sicklepod seeds per plant and seeds per m2. Imazaquin and chlorimuron plus metribuzin reduced sicklepod seeds per m2more than 50% at 0 or 2 wk weed-free intervals, compared with nontreated plants at these same intervals.

Cultural Practices and Glyphosate Applications for Sicklepod (Senna obtusifolia) Control in Soybean (Glycine max)1

“…The standard herbicide program reduced seed production by 38 to 91% compared with the weedy check in 1995 and 1996 but still allowed production of at least 75 seeds/m 2 in 1995 and 222 seeds/m 2 in 1996, which resupplied the soil seedbank. The seed reduction by the STD was similar to that reported by Shaw and Hydrick (1993). The glyphosate programs reduced seed production Ͼ 98% in 1995, except in the Aprilplanted soybean, where reductions were 86 to 93%.…”

“…Sicklepod seedling emergence increased by 7-, 21-, and 20-fold at 1, 2, and 3 yr, respectively, after seed production from a subeconomic threshold population (Johnson et al 1994). Even sequential applications of soil-and foliar-applied herbicides often failed to prevent seed production (Miller and Griffin 1994;Murdock and Toler 1992;Shaw and Hydrick 1993;Watts et al 1997).…”

Herbicides Reduce Seed Production in Reproductive-Stage Yellow Starthistle (Centaurea solstitialis)

“…Although the rosette-and bud-stage applications failed to eliminate seed production, the delay in flowering may appreciably reduce the quantity of yellow starthistle seed produced. Shaw and Hydrick (1993) reported that lateflowering sicklepod [Senna obtusifolia (L.) Irwin and Barnaby] plants lacked sufficient growing season to maximize seed production and viability. Yellow starthistle requires more thermal time (degree days) (Roché et al 1997) for flowering than most associated annual species, so that adequate late-season moisture, either stored in the soil or supplied as summer precipitation, is critical for optimizing reproduction (Borman et al 1992;Roché et al 1994).…”

Sicklepod (Senna obtusifolia) Interference with Soybean (Glycine max) Cultivars Following Herbicide Treatments

“…The success of sicklepod interference with soybean has been attributed to various aspects such as growth habit, physiological structure, and inherent ability to resist various herbicide treatments (Banks et al 1985;Shaw and Hydrick 1993). Sicklepod seeds will germinate at soil temperatures ranging from 24 to 36 C and soil pH levels from 3.2 to 7.9 (Creel et al 1968).…”