Kochia control in glufosinate-resistant canola

Single and sequential applications of glufosinate provided excellent control of Group 2 and Group 2 + 9 resistant kochia. Treatments containing sulfentrazone (which were experimental and not registered) caused excellent control but unacceptable crop injury. Layering strategies with ethalfluralin and/or carfentrazone followed by glufosinate may help reduce herbicide-resistant selection pressure on glufosinate in canola.

Herbicide-resistant kochia is evolving into a challenging weed to control in western Canada. Triple resistance to Groups 2 (ALS inhibitors), 9 (glyphosate) and 4 (synthetic auxins) have been confirmed on the Prairies. Recently, preliminary research has identified Group 14 herbicide-resistant kochia to the active ingredients saflufenacil, carfentrazone, pyraflufen, tiafenacil, saflufenacil + trifludimoxazin, sulfentrazone, and flumioxazin

Glufosinate-resistant canola (LibertyLink) offers an alternative herbicide Group 10 for herbicide-resistant kochia control since glufosinate-resistant kochia is not known to occur. The objectives of this study were to identify herbicide strategies in glufosinate-resistant canola to effectively manage ALS inhibitor-resistant kochia with or without glyphosate resistance, and to mitigate selection pressure for glufosinate-resistant kochia through the use of multiple effective herbicide sites-of-action. The research was initiated prior to the confirmation of Group 4 and 14 kochia resistance.

Field experiments were conducted in 5 environments near Lethbridge (2013 – 2015) and Coalhurst (2013 – 2014), Alberta. Weeds were controlled prior to seeding with a pre-seed burndown. Plots were seeded to glufosinate-resistant canola hybrid L120. Group 2 resistant kochia, with and without glyphosate resistance, were sown in split replicate plots.

Herbicide treatments compared were:

  • Ethafluralin (Edge Microactive) spring pre-plant (2013) or fall-applied (2014 + 2015)
  • Ethafluralin fall-applied + glufosinate post-emerge
  • Ethafluralin fall-applied + sulfentrazone (Authority) pre-plant
  • Ethafluralin fall-applied + carfentrazone (Aim) pre-plant + glufosinate post-emerge
  • Carfentrazone + sulfentrazone pre-plant
  • Carfentrazone + sulfentrazone pre-plant + glufosinate post-emerge
  • Glufosinate post-emerge at 1 to 2 leaf stage (1.35 or 1.59 L/ac; 500 or 590 g ai/ha)
  • Glufosinate at 1 to 2 leaf stage + glufonsinate at 5 to 6 leaf stage (1.35 L/ac; 500 g ai/ha)

Sulfentrazone is not registered for use on canola, and was included for research purposes.

Kochia plant densities were measured 2 weeks after canola emergence. Kochia control was assessed 3 weeks after post-emergence treatments. Control ratings were 60 to 70% suppression, 80 to 89% good control, and 90% or greater as excellent control.

Crop safety

The research found that treatments containing carfentrazone + sulfentrazone pre-plant resulted in canola injury and yield loss in some cases. In 2013, treatments containing carfentrazone + sulfentrazone reduced canola plant density by 49 to 66% at Lethbridge in 2013 compared to glufosinate post-emergent.

In 2014 and 2015, carfentrazone + sulfentrazone caused a 32 to 46% reduction in canola plant density compared to glufosinate post-emergent at Lethbridge. Treatments containing ethalfluralin, carfentrazone, or glufosinate had acceptable or no canola injury.

Excellent kochia control with glufosinate

In 2013, ethalfluralin alone provided the lowest kochia control at around 64 to 75%.  Ethalfluralin + glufosinate early had 75% control. Treatments with carfentrazone + sulfentrazone had higher control ratings from 75 to 95%, but the treatments were unacceptable due to canola injury and yield loss. Glufosinate alone treatments provided 91 to 92% control, while the sequential glufosinate treatment provided the highest control at 95%.

In 2014 and 2015 across all environments, ethalfluralin provided the poorest control at 38%. Similar to 2013, treatments with carfentrazone + sulfentrazone had good to excellent levels of control, but with unacceptable crop injury. Glufosinate early application provided 89 to 92% control, while glufosinate sequential applications provided 96% control. The ethalfluralin fall-applied + carfentrazone pre-emerge + glufosinate early had 93% control.

There were few differences in kochia control ratings between the populations with and without glyphosate resistance.

Canola yield

In 2013, the lowest yields occurred with treatments containing carfentrazone + sulfentrazone, because of crop injury due to sulfentrazone, yielding significantly lower than the untreated check. All other treatments were relatively similar ranging from 38 bu/ac to 41 bu/ac (2136 to 2281 kg/ha).

In 2014 and 2015, the lowest yield was the untreated check at 37.6 bu/ac (2111 kg/ha), while the highest yield occurred with the sequential glufosinate treatment at 55.6 bu/ac (3121 kg/ha). Ethafluralin + glufosinate yielded 52 bu/ac (2923 kg/ha), and the high rate of glufosinate alone yielded similar at 52.3 bu/ac (2937 kg/ha). Ethafluralin + carfentrazone + glufosinate yielded 53 bu/ac (2976 kg/ha).

Overall, a single post-emergent treatment at the early 1 to 2 leaf stage, or a sequential glufosinate post-emergent treatment provided excellent control of Group 2 and Group 2 + 9 resistant populations in glufosinate-resistant canola.

Layering fall-applied ethalfluralin and/or carfentrazone pre-plant with glufosinate post-emerge also provided excellent control. Layering is a strategy that can help reduce resistance selection pressure on glufosinate. However, with the preliminary confirmation of Group 14 resistance in kochia, and the heavy reliance on Group 14 herbicides in other crops where herbicide choices are limited, layering carfentrazone in glufosinate-resistant canola must be balanced off with carfentrazone selection pressure in other crops.

An additional layering strategy would be to use ethalfluralin fall applied followed by glufosinate post-emergent, which provided excellent control of kochia in this study. Since this study was initiated, topramezone + bromoxynil (Group 27 + 6) has been registered for kochia control before canola and could also represent another opportunity to diversify herbicide layering strategies targeting kochia in canola. Additionally, canola growers could prolong the usefulness of glufosinate by implementing non-chemical weed management strategies in an integrated weed management strategy.

Funding was provided by Alberta Canola Producers Commission, Alberta Grains (Alberta Barley Commission and Alberta Wheat Commission), Alberta Crop Industry Development Fund, BASF Canada, Nufarm Canada, Dow AgroSciences, Western Grains Research Foundation, and Valent Canada.

Ms. Alysha T Torbiak, Dr. Robert Blackshaw, Mr. Randall N Brandt, Dr. Bill Hamman, and Dr. Charles M. Geddes. Multiple herbicide-resistant kochia (Bassia scoparia) control in glufosinate-resistant canola. Canadian Journal of Plant Science. Just-IN

Open Access  https://doi.org/10.1139/cjps-2024-0008

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