Weed Control Programs in Drilled Glyphosate-Resistant Soybean¹

Abstract

Field studies were conducted in 19-cm-row soybean during 1997 and 1998 to evaluate the rate and timing of glyphosate applications applied alone at 0.42 and 0.63 kg ae/ha and with other herbicides to glyphosate-resistant soybean in terms of weed control, soybean yield, and net return. Weed species included barnyardgrass, hemp sesbania, pitted morningglory, and prickly sida. Among glyphosate-alone weed control programs, sequential applications generally provided the highest and most consistent control of all species evaluated (above 90% for broadleaf species). Glyphosate applied in combination with selective postemergence (POST) herbicides or following soil-applied herbicides controlled most species comparable to sequential glyphosate applications. Most herbicide programs, except for single glyphosate applications, were comparable to sequential glyphosate applications in terms of soybean yield and net return and ranged from 2,221 to 2,827 kg/ha and $410.28 to $549.60/ha. Depending on the year, either one or two glyphosate applications were needed for adequate weed control in programs with a soil-applied herbicide. Glyphosate rate affected neither weed control, yield, nor net return. Depending on a producer's management style and weed spectrum, weed control programs with glyphosate alone, in combination with another POST herbicide, or following soil-applied herbicides are all viable options in drilled glyphosate-resistant soybean.

Comparison of weed control strategies in glyphosateresistant soybean [Glycine max (L.) Merr.] in Atlantic Canada

“…However, such treatments may be beneficial if the density of weeds in the second flush is great. Sequential glyphosate treatments provided 89 to 100% weed control in both years and were more effective than the single treatment in 1998, supporting findings of Wait et al (1999) and Payne and Oliver (2000) that sequential treatments result in greater and more consistent weed control. Wiesbrook et al (2001), however, found that sequential treatments of glyphosate gave no advantages over single applications in weed control or soybean yield.…”

“…Research in the USA has shown that weed control with glyphosate is affected more by rate than time of application (Ateh and Harvey 1999;Mulugeta and Boerboom 2000;Vangessel et al 2000;Krausz and Young 2001). Sequential applications have provided greater and more consistent weed control than have single applications (Wait et al 1999;Payne and Oliver 2000;Wiesbrook et al 2001). However, level of weed control was dependant on time of application of single treatments and on crop row width, with Abbreviations: CHU, corn heat unit 1199 greater control at narrow-row spacings (Ateh and Harvey 1999;Young et al 2001).…”

“…Soybean yield is affected by level and time of removal of weed competition. In narrow-row glyphosate-resistant soybean, a well-timed single glyphosate application can prevent yield loss (Mulugeta and Boerboom 2000;Payne and Oliver 2000;Vangessel et al 2000). In areas where there is a low accumulation of CHU, such as in Atlantic Canada, cultivars that require longer seasons may not mature and weed competition, caused by a delay in herbicide application or injury from applied herbicides during early stages of growth, could reduce crop yields.…”

Germination ecology of Ambrosia artemisiifolia L. and Ambrosia trifida L. biotypes suspected of glyphosate resistance

“…Other explanations for weed escapes are that some weed species continue to germinate for a long time during the growing season, including after the last glyphosate application [11,33,34]. This means that certain weed biotypes escape the glyphosate treatment simply by avoiding the herbicide application; so timing of the glyphosate applications is the key to its efficacy [35]. The observed glyphosate failures in controlling ATSR biotype under field conditions were due to ecological escape phenomena or to other factors (environmental conditions, incorrect spraying application) which have limited the phyto-toxic effect of the herbicide.…”

Leaf area and epicuticular wax content of Sida spp

“…At the reproductive stage (R), no difference was found for SLA between species, with mean equal to 113.24 cm 2 /g (Table 2). Thus, results could help in understanding the aggressive competitive ability of S. spinosa in crops like cotton (Chandler, 1977) and soybean (Payne and Oliver, 2000).…”