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Kochia Loves This Drought!

herbicide resistant kochia
A young Kochia plant.
Weed Wisdom
By Dr. Charles Geddes

Kochia enjoys a dry, hot year. There is less competition from the crops. Due to the lack of precipitation this year, many crops have experienced inhibited growth which leaves more resources available to the pesky weed.

What is causing this?

While the heat has a negative impact on crops, the opposite can be said for kochia. Because of the excessive heat, post-emergence herbicides have reduced efficacy.

“There’s a couple reasons for this. First, plants tend to shut down in stressful environments. The plant stomata close up to prevent water loss. They are, therefore, not taking in the pesticide and thus efficacy is reduced,” said Ken Coles, Farming Smarter Executive Director. “There’s also a second issue with getting the product to the plant. High heat creates a high propensity for both evaporation of small spray droplets, which reduces pesticide coverage, but it also may cause the active ingredients to volatize depending on the product.”

While excessive heat affects weeds that same way it affects crops, kochia has the advantage of not metabolizing herbicides as easily as it would under normal conditions. Heat isn’t the only advantage kochia has against crops – it also has a considerable advantage against pests.

Across Alberta, we’re seeing hordes of grasshoppers devour crops, devastating yields. Kochia largely remains unharmed. Previous studies show that kochia plants resist feeding damage from grasshoppers. Grasshoppers tend to only eat the old leaves and avoid the new leaves. This only amplifies the effect this drought has on kochia development.

Preventing seed production and spread of kochia will be critical this year. The plants have not had much competition from crops. Limiting opportunities for the seedbank to replenish is critical as it will aid in curbing problems in subsequent years.

Additionally, with current conditions, there is less stubble to catch tumbleweeds. Limiting travel of tumbleweeds is also important to reduce the spread of possible intrinsic herbicide resistant traits.

“Each tumbleweed (mature kochia broken off and rolling in the wind) can carry as much as 30,000 seeds. These seeds can carry a diverse mix of genetic traits. When the tumbleweeds travel long distances, they deposit seeds over a large area. If some seeds are herbicide resistant, this can spread those resistant genes a long way,” says Lewis Baarda, Farming Smarter Field Tested Manager.

Glyphosate resistant Kochia in southern Alberta. Note the lines created by tumbling kochia.

What can be done to stop kochia?

Currently, the best way to combat kochia from taking over is to cut it down. Our research is showing that cutting the plants near the end of August can help prevent the production of viable seeds. After cutting the plant, spraying with a post-cutting herbicide can mitigate regrowth of the patch, adding to the effectiveness of the treatment.

As well as reducing the likelihood of the plant growing viable seeds, cutting the plant at the growing point also eliminates the tumbleweed growth structure. This makes it less able to blow away in the wind, further preventing the spread of herbicide resistant seeds.

Kochia is the third most abundant weed in southern Alberta. Weather like we are seeing now only helps aid its resistance against our practices to cull them. Fortunately for us, there is more than one way for us to fight back against them.

Currently, Farming Smarter has a project underway looking at combating the populations of triple-resistant kochia rapidly expanding across the prairies. To learn more about what you can do to protect your farm, take a look at the Managing Herbicide Resistant Kochia project.