Global Agriculture

Weed of the Year? Three Tips for Dealing with Kochia

30 June 2021, EU: A couple of years ago, I wrote a series of blogs under the heading The Weed of The Week. This blog today might very well be titled The Weed of the Year. From what I have seen in the fields, along with the phone calls and texts that I have received this year, Kochia (which I previously referred to and wrote about as the Scourge of the South) is showing up across most of the south and large areas of the dark brown and black soil zones.

Enquiries have varied from “What is this weed?” to “How do I control it in XXX crop?” The first question is easy to answer.

Kochia – an olive mat of weeds to a velvety green blanket of weeds. Kochia (Kochia scoparia) is a weed native to Asia and central Europe. Unlike most weeds, it was introduced to Canada as an ornamental plant by European immigrants and is sold by seed companies as burning bush and in nurseries with annual plants to this day. In fact, I saw it in a nursery where I buy my annuals this year.

The second question is easy as well as some of the crops – flax, Clearfield (CF) Canola, or sunflowers do not offer any in-crop alternatives. Your choice for control in these crops includes:

  • tillage
  • burn off with glyphosate + heat
  • or cutting for feed

None of these options appeal to growers, especially with today’s commodity prices.

What sets Kochia apart from most weeds is:

Prolific seed production – Kochia reproduces from seeds; it typically produces around 15,000 seeds per plant! Seeds are dispersed in the fall when the plant matures. If left undisturbed, it becomes a tumbleweed.  Often, it is processed by the combine, acting as an efficient distributor of the seed. At times, areas are swathed and then harrowed up into a pile for burning. Some seeds may be left in the harrows and transported to another area of the field.  I can’t count the number of times I have discovered Kochia in a previously clean field and the farmer announces, “Oh yeah, last year I moved over from Mike’s Dad’s ¼ and must have dragged it over.”  On the positive side, Kochia seeds are somewhat short-lived in the soil.  They only last 2-3 years, so if you can control them for a couple of years, the seed supply will play out.

Tolerance – Kochia is tolerant to drought and has a high tolerance to saline soils. Saline rings around slough or along the headlands next to a ditch are locations where you can typically observe it in a field. Over the last couple of years, populations have increased due to two factors: a wide-ranging drought and increasing salt-affected or saline soils.

Outcrossed – Not only does Kochia produce a large number of seeds, but it is also outcrossed. This means that it required pollen from another plant to be pollinated and produce seed. Kochia produces a large amount of pollen; because of this and a high amount of genetic variability, it is a prime candidate to become resistant to herbicides. It quickly became resistant to Group 2 ALS inhibiting herbicides in the ’90s and, more recently, to glyphosate or Group 9s and dicamba, a Group 4 herbicide. A Kochia survey in southern Alberta in 2017 found that all Kochia populations were resistant to Group 2s, 50% of populations were resistant to Group 9 glyphosate, and 18% of populations resistant to Group 4 (dicamba) herbicides. More shocking was that there were Kochia populations with triple resistance to Group 2, Group 4, and Group 9 modes of action found in 10% of the 305 populations collected and tested.

Planning for 2022

With that as a background, now is a great time to plan around a potential Kochia problem in 2022. Here’s how:

1. Map out the patches or areas of fields that are infested.

2. Use this information when planning your 2022 crops.

Kochia is a lot easier to control in cereals compared to many other crops. There are several herbicides available that do an excellent job at controlling Kochia in a crop.

This year, Authority 480 herbicide was labelled for wheat. It provides residual control of Kochia and a few other weeds. It can be applied pre-plant or up to three days after seeding, and it can be done alone or with glyphosate. In addition to Kochia, Authority controls redroot pigweed, lamb’s-quarters, cleavers, and wild buckwheat.  Authority is also registered for use in field peas, chickpeas, flax, soybeans, and sunflowers. This is important because there are no effective in-crop alternatives for flax, sunflowers, or chickpeas.

Another product that can provide good to excellent control of Kochia is Edge (ethalfluralin). It is registered on canola, field peas, lentils, faba beans, yellow mustard, dry edible beans, sunflowers, alfalfa (establishment), soybeans, chickpeas, dry common beans, and industrial hemp. Canola should be of interest to growers as there are no in-crop herbicides for Kochia control in Clearfield (CF) Canola.

Keep in mind, if Roundup Ready (RR) canola is grown in an area where Group 9 resistant Kochia is suspected, there will be no control options.

3. Finally, manage the problem areas this year. This may include spraying out patches of uncontrolled Kochia in fields, tilling them up, or mowing prior to seed set (early July). Burning in the fall also works, but try and avoid harrowing. If you use pre-harvest weed management with glyphosate, be sure to note any Kochia that seems to be unaffected. 

Control strategies for crops with limited control alternatives:
1. Good control of Kochia in the previous year’s crop.
2. Use a burn-down up to emergence.
3. Use products containing sulfentrazone (Authority). They have excellent Kochia control and can be used in many crops reduced and no-till systems.
4. Ethalfluralin control of Kochia is rated as fair but can perform very well. You’ll get the best results when applied in the fall.
5. Choose Kochia-free fields or use a registered pre-emergent option for crops such as flax or CF Canola.