While there’s no silver bullet, certain chemical and cultural practices can manage the worst impacts of this weed and help contain its spread.
Everyone knows that kochia is a challenging weed in Western Canada. It emerges in cool spring soils before crops are even planted. It produces seed prolifically and disperses it widely. Kochia shrugs off dry, hot and saline conditions and thrives when crops struggle. Herbicide resistance takes several useful chemistries out of the toolbox.
Having studied kochia for years, Charles Geddes would be the last person to minimize the headaches associated with this weed.
Even so, the Lethbridge-based Weed Scientist with Agriculture and Agri-Food Canada is inclined to see kochia as a glass-half-full situation. Despite the challenges, there’s still lots that growers can do. His research points the way.
Herbicide and cultural practices
Dr. Geddes and his team looked at managing kochia through the span of a four-year crop rotation – wheat, canola, wheat, lentils – integrated with cultural and chemical practices, in order to develop management strategies taking advantage of the biology and ecology of kochia,
The research team mapped out how to use available modes of action in combinations that would hold back resistance pressure – using pre-emergent, post-emergent, in-crop, pre-harvest or post-harvest application, known as herbicide layering.
A well-chosen crop rotation helps keep kochia on the defensive, and fall-planted crops shouldn’t be overlooked.
Dr Geddes has also looked at crop rotation diversity. In one experiment of a spring wheat, canola, spring wheat, lentils rotation they swapped out spring wheat with winter wheat. “We’re trying to promote a competitive crop rotation,” says Geddes, “because kochia tends to respond to crop competition. It responds by reducing the amount of seed the plant produces. Winter wheat can be competitive in the spring with kochia that’s just trying to emerge. Winter wheat is also harvested before kochia produces viable seed.”
Two means of increasing crop competitiveness were found to be effective in combatting kochia: narrower row spacing and increasing seeding rate. This is evidence that kochia backs down when the going gets tough.
“Decreasing row spacing showed a 60% decrease in kochia biomass in all crops,” says Geddes. “Adding in this cultural management is essentially like adding another herbicide to the tank.” Seeding rates combined with herbicide management can help reduce the potential for resistance in kochia.
However, if only one farmer in a region is diligent about the above kochia management practices, their efforts are unlikely to see much payback. After all, kochia is a prolific seed producer and spreader. Kochia seed blowing in from less-attentive neighbours would prevent much improvement.
That’s why Charles Geddes would like to see more farmers working on this problem together.
“There’s a lot of opportunity for community-based strategies,” says Geddes. “For example, all farmers in a certain area could commit to manage kochia effectively for a few years in a row. Combined with chemical and cultural practices, this could make a big difference over time.”