Influence of Seeding Rate and Herbicide Treatments on Weed Control, Yield, and Quality of Spring‐Seeded Glyphosate‐Resistant Alfalfa

Abstract

Field trials were conducted in 2005 and 2006 in central and southwest Missouri to investigate the eff ect of seeding rate and herbicide programs on weed control, forage quality, and yield within the year of establishment in spring seeded glyphosate-resistant (GR) alfalfa (Medicago sativa L.). In all experiments, EPTC (4.4 kg ha -1 ), 2,4-DB plus sethoxydim (1.1 plus 0.21 kg ha -1 ), imazamox (0.043 kg ha -1 ) and glyphosate (0.86 kg ae ha -1 ) were applied to GR alfalfa that was seeded at 4.5, 8.9, 13.5, and 18 kg ha -1 . Across all locations, the glyphosate application provided good control of weeds regardless of alfalfa seeding rate. When applied at the same timing, imazamox provided similar levels of annual broadleaf weed control as glyphosate, while 2, 4-DB plus sethoxydim provided similar levels of annual grass and broadleaf weed control as glyphosate. Neither glyphosate nor the conventional herbicide treatments reduced alfalfa stem density between the fi rst and last annual harvests, but 2, 4-DB plus sethoxydim resulted in the most visual injury to seedling alfalfa stands and lowered initial yields at all locations. In addition, alfalfa annual yields were similar or higher in the glyphosate treatment compared to the other herbicide programs. Harvested forage in the herbicide treatments generally had greater crude protein (CP) content than the untreated control forage. Application of glyphosate resulted in similar or higher forage CP content compared to conventional herbicide treatments. In vitro true digestibility of the harvested GR alfalfa ranged from 750 to 860 g kg -1 DM at all locations with few diff erences across herbicide treatments.

The Effects of Seeding Rate on Older Stands of Glyphosate‐Tolerant Alfalfa

“…Over the 5 yr of the study, glyphosate‐treated plots produced 1.5 Mg ha −1 more alfalfa than the non‐glyphosate plots and 7.4 Mg ha −1 more alfalfa than the plots that received no herbicide. This is consistent with findings from McCordick et al (2008) and Bradley et al (2010) who reported higher alfalfa yields from glyphosate‐treated alfalfa than alfalfa treated with a non‐glyphosate herbicide. Total forage yield over the 5 yr of the study was also greater when herbicides were used during alfalfa establishment than when no herbicide was used (Fig.…”

“…Recently emerged alfalfa seedlings grow relatively slow and are very susceptible to competitive suppression by weeds germinating with or shortly after the crop (Fischer et al, 1988; Gianessi et al, 2002). Weed competition reduces the total‐season alfalfa yield compared to when weeds are controlled with a herbicide (Sheaffer et al, 1988); however, total forage (alfalfa + weeds) yields in the seeding year are often greater when no herbicides are used, due to higher weed yield (Wilson and Burgener, 2009; Bradley et al, 2010; Dillehay and Curran, 2010; Hall et al, 2010).…”

“…Glyphosate‐tolerant alfalfa provides a new weed control tool that provides not only a wider application window for effective weed control but also excellent crop safety. Glyphosate is less injurious to spring‐seeded GT alfalfa than other herbicides are to non‐GT alfalfa (McCordick et al, 2008; Bradley et al, 2010).…”

Widening the analysis of Energy Return on Investment (EROI) in agro-ecosystems: Socio-ecological transitions to industrialized farm systems (the Vallès County, Catalonia, c.1860 and 1999)

“…prunings from vineyards and grape pomace. Estimations of weed production come from Guzmán et al (2014) except for alfalfa in 1860, which employ values from organic forage (Sheaffer et al, 2014) and in 1999 from conventional farming using the herbicide Lamazox (Bradley et al, 2010).…”

Evaluation of Various Pre-emergent and Post-emergent Herbicides on Five Summer Legumes

“…Temme et al (12) observed 234 lb/acre increase in alfalfa ( Medicago sativa L.) dry matter (DM) yield when instituting herbicide treatments for weed control. Additionally, up to a 21% increase in forage crude protein (CP) has also been observed in legume forage trials where chemical weed control was implemented (3). Experimental applications of herbicides to non‐labeled summer legumes could result in novel findings through forage injury and weed control evaluation.…”