Glyphosate- and acetolactate synthase inhibitor-resistant kochia (Bassia scoparia) control in field pea

Kochia [Bassia scoparia (L.) A.J. Scott] is an invasive C-4 tumbleweed in the Great Plains of North America, where it impedes crop harvest and causes significant crop yield losses. Rapid evolution and spread of glyphosate-and acetolactate synthase (ALS) inhibitor-resistant kochia in western Canada limit the herbicide options available for control of these biotypes in field pea (Pisum sativum L.); one of the predominant pulse crops grown in this region. Field experiments were conducted near Lethbridge, Alberta, in 2013-2015 and Coalhurst, Alberta, in 2013-2014 to determine which herbicide options effectively control glyphosate- and ALS inhibitor-resistant kochia in field pea. Visible injury of field pea was minor (0%-4%) in all environments except for Lethbridge 2013, where pre-plant (PP) flumioxazin and all treatments containing post-emergence (POST) imazamox/bentazon resulted in unacceptable (14%-23%) visible injury in field pea. Herbicide impacts on field pea yield were minor overall. Carfentrazone + sulfentrazone PP and saflufenacil PP followed by imazamox/bentazon POST resulted in >= 80% visible control of kochia in all environments, while POST imazamox/bentazon alone resulted in >= 80% reduction in kochia biomass in all environments compared with the untreated control (albeit, absent of statistical difference in Coalhurst 2014). These results suggest that layering the protoporhyrinogen oxidase-inhibiting herbicides saflufenacil or carfentrazone + sulfentrazone PP with the ALS- and photosystem II-inhibiting herbicide combination imazamox/bentazon POST can effectively control glyphosate- and ALS inhibitor-resistant kochia in field pea while also mitigating further selection for herbicide resistance through the use of multiple effective herbicide modes-of-action.

Automated summary

Kochia is an invasive weed in North America that affects crop harvest and yield losses. The use of herbicides in western Canada is limited due to the rapid evolution of glyphosate and ALS inhibitor-resistant kochia. Field experiments were conducted to determine effective herbicide options for controlling kochia in field pea. The results showed that the combination of carfentrazone + sulfentrazone with imazamox/bentazon can effectively control resistant kochia in field pea, while also mitigating herbicide resistance.