Timing of pre-seeding glyphosate application in direct-seeding systems

Abstract

Direct-seeding systems are growing in popularity on the Canadian prairies, a trend that can be attributed to the low cost of glyphosate, reduced labor, fuel, and equipment requirements, and to a lesser extent improved soil moisture and soil quality conservation (Zentner et al. 1996). Weed management is an integral component of direct-seeding systems (Brandt 1992;Derksen et al. 1996;Moyer et al. 1994). Pre-seeding glyphosate applications are a critical practice to ensure optimal weed control and crop productivity in directseeding systems.An application of glyphosate in May rather than April extended the weed-free period following application and resulted in the lowest weed density among different cover crop residues (Blum et al. 1997). O'Donovan et al. (1985) found that barley and wheat yield decreased by 3% for each day that wild oat (Avena fatua L.) emerged before the crop. Limited evidence indicates that glyphosate application should be timed just prior to sowing or emergence to ensure that most weeds emerging before the crop are controlled. However, direct seeders have reported that additional weed control with sweeps rather than narrow-hoe openers allows them to apply glyphosate a week or more prior to seeding rather than immediately prior to seeding or emergence without any penalty to weed control and crop productivity. Also, Producers are interested in whether crop productivity can be maintained with pre-seeding glyphosate application 2 to 3 wk prior to direct seeding with sweeps. A wider window for glyphosate application would be beneficial, particularly for producers with a large number of hectares. An experiment was conducted at Scott and Melfort, SK, Canada, in 1997 and 1998 to assess glyphosate application 2 to 3 wk before, 1 d before, and 3 to 4 d after (just before crop emergence) the time of seeding in narrow-hoe and simulated-sweep (cultivation immediately followed by a narrow-hoe drill) direct-seeding systems. Wheat grain yield was 25% lower when glyphosate was applied 2 to 3 wk before rather than just prior to seeding only with the narrow-hoe direct-seeding system at Scott in both years. This yield reduction corresponded with the greater median grass weed fresh weight. Yields were 15% lower for both direct-seeding systems at Scott when glyphosate was applied 3 to 4 d after seeding. Barley grain yield was 46% greater (1997) or 25% lower (1998) in the narrow-hoe compared with the simulated-sweep directseeding system at Melfort. These yield responses corresponded with opposite responses for median grass weed fresh weight. The tillage effect of sweeps at the time of seeding can improve the control of grass weeds compared with seeding implements equipped with narrow hoes. However, a narrow-hoe system with glyphosate applied just prior to sowing consistently provided the greatest cereal yields. . À Scott, le rendement grainier du blé a diminué de 25 % les deux années, quand le glyphosate a été appliqué deux à trois semaines avant les semis plutôt qu'immédiatement avant avec le système d'ensemencement ...

Effect of Herbicides on Field Violet (Viola arvensis) in Direct-Seeded Spring Wheat

“…Wheat seed yield and biomass were not consistently affected by POST or PREPLANT herbicides to control field violet. PREPLANT herbicides have been shown to improve crop yield by reducing interference from weeds at the critical period of establishment (Johnson et al 2002;Martin et al 2001). Weeds emerging after PRE-PLANT herbicide application and before canopy closure may have limited the effectiveness of this strategy in our experiments.…”

Occurrence and levels of glyphosate and AMPA in shallow lakes from the Pampean and Patagonian regions of Argentina

“…In addition to the overwhelming adoption of NTF practices, the use of glyphosate has been favored by the price drop due to the expiration of its patent in 2000 and the increasing number of glyphosate manufacturers. Glyphosate-based herbicides (GBH) are mainly applied over summer and winter crops, as well as during the fallow period (Johnson et al, 2002;P erez et al, 2017). Besides its use in agriculture and silviculture, glyphosate is also used for the maintenance of public spaces (parks, gardens) and for aquatic weed control (Held et al, 2016;Kogan and Alister, 2010;Tasker, 1995).…”

Comparison of a Glyphosate-Resistant Canola (Brassica napusL.) System with Traditional Herbicide Regimes

“…This risk may be higher under zero-compared with conventional-tillage systems because multiple glyphosate applications are more likely. There is increasing evidence that timing of the glyphosate applications based on rational assessments of weed emergence patterns is more important than the total number of applications in both canola (Clayton et al 2002;Harker et al 2004;Johnson et al 2002) and soybean (Swanton et al 2000). With appropriate timing, our study and others also indicate that two glyphosate applications (pre-seed and once in-crop, or twice in-crop) would, in most cases, be sufficient to optimize weed control, crop yield, and economic return.…”