Soybean response to weed interference and defoliation

Abstract

Field experiments were conducted in Louisiana over 2 yr to evaluate the influence of full-season interference from johnsongrass, common cocklebur, or hemp sesbania at densities of 2.5, 0.5, and 2.0 plants m–1of row, respectively, and simulated insect defoliation of soybean on weed and soybean growth. Defoliation at R2 (full bloom) and R5 (beginning seed development) soybean growth stages was accomplished by removal of zero, one, or two leaflets per soybean trifoliate, which approximated 0, 33, and 66% defoliation, respectively. Height and dry weight of all weeds were not affected by soybean defoliation level or defoliation stage. Soybean height 3 wk after defoliation at R5 was not influenced by weed interference, soybean defoliation level, or defoliation stage in either year. Averaged across soybean defoliation levels and stages in 1994, johnsongrass, common cocklebur, and hemp sesbania reduced soybean yields 30, 15, and 14%, respectively. In 1995, johnsongrass reduced soybean yield 35%. As soybean defoliation level increased, a linear decrease in soybean yield was observed. Averaged across weeds and soybean defoliation stages, 33 and 66% defoliation reduced soybean yield 6 and 20% in 1994 and 12 and 33% in 1995, respectively. Defoliation at R5 resulted in 10% lower yield than defoliation at R2 in one of two years. Yield reduction due to combinations of weeds and soybean defoliation was additive.

Augmentation of soil detritus affects the spider community and herbivory in a soybean agroecosystem

“…Soybeans are reasonably tolerant of leaf damage and the levels we observed here are unlikely to have economically important effects on yield (Turnipseed, 1972; Kogan & Turnipseed, 1980). Nevertheless, under certain conditions, specific cultivars experience sufficient insect damage to affect yield (Eckel et al., 1993; Lambert & Heatherly, 1995; Haile et al., 1998; Grymes et al., 1999). For example, in years with low rainfall, soybean yield is much more sensitive to defoliation (Lambert & Heatherly, 1995; Haile et al., 1998).…”

“…As global climate change creates less predictable rainfall, the importance of soil manipulations to soybean production may increase. In addition, weed interference and defoliation have additive effects on soybean harvest (Grymes et al., 1999). Thus, our manipulations, which were coupled with the planting of additional weeds in order to minimize the differences between till and no‐till plots, may have implications for particularly weedy situations when production is more sensitive to differences in leaf damage.…”

Early-season insect defoliation influences the critical time for weed removal in soybean

“…Delay in canopy development allows more light transmittance, which can favor weed growth and competition directly affecting weed management programs. Others have studied effects of defoliation and weed-interference on soybean during late-season growth (e.g., reproductive growth stages) (Grymes et al 1999;Helm et al 1992;Higgins et al 1984). No research has specifically addressed the impact of early-season insect defoliation on the need for timing of weed control.…”

Modeling Growth and Yield of Crops Using Different Tillage Systems

“…In geometrical terms, LAI represents the sum of plain side of a leaf area contained in a matured leaf per geographical area of a group of crops. It is generally defined as the ratio of leaf area to land area and is strongly related to crop yield [59][60][61][62][63]. Thus, the system of assessing development association among plants growing together is referred to as LAI.…”