Light Interception and Yield Response of Ultra-Short–Season Soybean to Diphenylether Herbicides in the Midsouthern United States¹

Abstract

Full canopy closure and light interception are critical to obtaining full yield potential of ultra-short–season soybean in the midsouthern United States. We hypothesized that herbicide applications that resulted in soybean leaf injury would reduce season-long light interception and yield of ultra-short–season soybean grown in this environment. Experiments were conducted in 2001, 2002, and 2003 at Fayetteville, AR, to determine the effect of the diphenylether herbicides acifluorfen and lactofen on light interception and yield of maturity group (MG) 0 and II soybean. Factors evaluated included soybean MG, herbicide rate, treatment timing, and soybean seeding density. When applied at soybean growth stage (GS) V3, 0.2 kg ai/ha lactofen reduced green leaf area immediately after application and final canopy closure relative to soybean treated with 0.6 or 0.2 kg/ha acifluorfen and untreated soybean. Herbicide application did not affect yield of well-watered soybean when applied at GS V3 in 2001 or at early reproductive development in 2003. In 2002, an irrigation problem resulted in a period of water-deficit stress during seed fill of MG II soybean. Under these conditions, treatment with acifluorfen at GS V3 reduced soybean yield, and treatment with lactofen during early reproductive development reduced soybean yield, relative to untreated soybean. This research indicates that diphenylether herbicides can be safely applied to well-watered ultra-short–season soybean, but yield reduction can occur when applied to soybean that is not well watered.

Input‐based Stress Management Fails to Increase Soybean Yield in Kentucky

“…Lee et al (2008) showed that if canopy light interception approached 90% at R1 and reached 95% by R5, maximum yield would result, likely explaining the similarity in yields. These results for lactofen application during early vegetative growth are similar to previous research showing no yield differences (Harris et al, 1991; Wichert and Talbert, 1993; Nelson et al, 2002; Edwards and Purcell, 2005). Additionally, lactofen‐treated plants were visually similar to untreated plants and application of lactofen did not affect branch nodes, branch pods, or branch seeds, indicating that the lactofen did not damage the apical meristem or affect soybean branching.…”

“…While numerous studies have shown the importance of branching in soybean yield determination (Herbert and Litchfield, 1982; Board et al, 1990; Carpenter and Board, 1997; Frederick et al, 2001); to our knowledge, no peer‐reviewed studies have shown that lactofen application destroys the apical meristem and increases branching. Previous studies have failed to show a yield increase for soybean treated with lactofen in the absence of yield‐limiting weed densities (Harris et al, 1991; Wichert and Talbert, 1993; Dann et al, 1999; Nelson et al, 2002; Edwards and Purcell, 2005).…”

Impact of postemergence herbicides on soybean injury and canopy formation

“…Full canopy formation is achieved when 95% of available light is intercepted by the crop (Gardner et al 1985;Harder et al 2007;Shibles and Weber 1965). This level of light interception is needed to maximize soybean yield and strongly suppress weed emergence (Edwards and Purcell 2005;Jha and Norsworthy 2009). The interception of solar radiation by the crop canopy impacts light quality reaching the soil surface and weed seeds lying on or near the soil surface.…”

Early‐Season Lactofen Application Fails to Increase Soybean Yield under Weed‐Free Conditions

“…Nelson and Renner (2001) observed decreases in soybean leaf area index (calculated from light interception measurements) and seed yield across multiple years for herbicide treatments containing lactofen. A study in Arkansas also observed decreased canopy closure (light interception) for soybean treated with lactofen during early-vegetative growth for MG 0 and MG 2 soybean, but yields were unaffected (Edwards and Purcell, 2005a).…”

“…Canopy images analyzed with Sigma Scan Pro 5.0 (Systat Inc, Richmond, CA) using a macro that automated the analysis process for a large number of images (Karcher and Richardson, 2005). The software was used to quantify the fraction of green pixel to total pixels in an image which was assumed to have a one-to-one relationship with the percentage of light intercepted by the soybean canopy (Edwards et al, 2005b). Prior to harvest, plant height measurements were taken at three locations within each plot.…”