How to manage herbicide-resistant kochia

Gardeners introduced kochia (Kochia scoparia) to North America as an ornamental in the 1800s. The large weed emerges early, grows rapidly and can tolerate salinity, drought and heat. Kochia often takes over saline or otherwise marginal areas where crops struggle to provide competition. When left to mature, kochia plants break off their stems and tumble with the wind, spreading seeds over a wide area.

Each kochia plant produces at least 15,000 seeds, often many more. Agriculture and Agri-Food Canada researchers (Robert Blackshaw et al) showed that kochia in dense patches with low crop competition can produce millions of seeds per square metre. Blackshaw also found that most kochia seeds will germinate or die within one to two years, so growers can quickly reduce the soil seedbank with management steps to prevent kochia from setting seed.

Resistance to multiple herbicide groups
Glyphosate-resistant kochia, confirmed in Southern Alberta in 2011, was the first glyphosate-resistant weed in Western Canada.

With kochia, glyphosate resistance builds on a sliding scale, increasing with subsequent non-lethal applications. For example, if kochia survives a 1X rate of glyphosate, offspring from that population may survive a 2X or 4X rate, and so on. (This applies only to glyphosate resistance.)

Agriculture and Agri-Food Canada surveys weed populations and the rise of resistance. The Alberta survey of 2021 found 78 per cent of kochia had some degree of glyphosate resistance. The Saskatchewan survey of 2019 found 87 per cent of kochia had glyphosate resistance. Manitoba was 58 per cent in 2018 in the same Glyphosate-or auxinic-resistant kochia and Russian thistle Prairie survey. Those numbers are likely to increase in the next round of surveys.

Agriculture and Agri-Food Canada researchers (Charles Geddes et al) confirmed a population of kochia in Saskatchewan in 2021 with resistance to Group-14 saflufenacil, and recently confirmed resistance to Group-14 carfentrazone and sulfentrazone. Group-4 resistance was confirmed in 2015, and almost all kochia is Group-2 resistant. Many kochia populations have stacked resistance to multiple groups. Kochia was always a hard weed to control. The job is much harder now.