A couple of years ago I wrote a number of articles under “The Weed of The Week” heading.
This column might be headed “The Weed of the Year.” From what I have seen in the fields, and from phone calls and texts I have received, kochia, which I have previously referred to 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 is easy. Descriptions include an olive mat of weeds to a velvety green blanket of weeds. The second question is easy as well because some crops — flax, Clearfield canola or sunflowers do not offer any in-crop alternatives. Your choice for control in these crops include tillage, burn off with glyphosate and Heat, or cutting for feed. None of these are options a grower wants to hear, especially with today’s commodity prices.
Kochia (Kochia scoparia) like many of our weeds, is native to Asia and central Europe. Unlike most weeds, though, it was introduced to Canada as an ornamental planting by European immigrants. It is still sold by seed companies as burning bush and in nurseries selling annual plants. I saw it in a nursery where I buy my annuals this year.
What sets kochia apart from most weeds is firstly, its 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, though, it is put through the combine that acts as a very good distributor of the seed. As well, sometimes 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 times I have discovered kochia in a field that was previously clean and have the farmer say “Oh yeah, last year I moved over from Mike’s Dad’s quarter and must have dragged it over.”
On the positive side, kochia seeds are somewhat short-lived in the soil. They last only two to three years, so if you can control them for a couple of years, the seed supply will play out.
The second factor is that kochia is tolerant to drought and has a high tolerance to saline soils. That is usually where you see it in a field, in that saline ring around a slough or along the headlands next to a ditch. Over the last couple years, populations have increased due to both of these factors, a wide ranging drought and increasing salt affected or saline soils.
The third factor that makes kochia a concern is that, not only does it produce a huge amount of seeds, it is also outcrossed. This means that it required pollen from another plant to be pollenated 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 for becoming resistant to herbicides. It quickly became resistant to Group 2 ALS inhibiting herbicides in the 1990s and more recently, to glyphosate or Group 9s and to dicamba, a Group 4 herbicide.
A kochia survey in southern Alberta in 2017 found that all kochia populations were resistant to Group 2s, 50 percent of populations were resistant to Group 9 glyphosate, and 18 percent 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 percent of the 305 populations collected and tested.
Now is the time to plan around a potential kochia problem in 2022. The first thing to do is map where the patches or fields are that are infested. Job Two is to use this information when planning your 2022 crops.
Kochia is a lot easier to control in cereals than many other crops. There are a number of herbicides available that do an excellent job at controlling kochia in 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 applied 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 also important because there are no effective in-crop alternatives for flax, sunflowers or chickpeas.
Another product that will provide good to excellent control of kochia is Edge (ethalfluralin) and is registered on canola, field peas, lentils, fababeans, 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 canola. As well, if Roundup Ready canola is grown in an area where Group 9 resistant kochia is suspected, there will be no control options.
Finally, manage the problem areas this year. This may include spraying out patches of uncontrolled kochia in fields, tilling them up or mowing before seed set in early July. Burning in the fall also works but avoid harrowing.
If you use pre-harvest weed management with glyphosate, make sure you notice any kochia that seems to be unaffected.
Here are some control strategies for crops with limited control alternatives:
- Seed in fields that showed good control of kochia in the previous year’s crop.
- Use a burn down up to emergence.
- Products containing sulfentrazone (Authority) have excellent kochia control and can be used in many crops in reduced tillage and no-till systems.
- Ethalfluralin control of kochia is rated as fair but can perform very well. Best results when applied in the fall.
- Use a registered pre-emergent option for crops such as flax or Clearfield canola.
Thom Weir PAg is a certified crop advisor and professional agrologist in the Yorkton, Sask., region. You can reach him at firstname.lastname@example.org.