By Shannon Chant P.Ag., Crops Extension Specialist, Swift Current
Kochia plants have been easy to find in the last few years in Saskatchewan. Unfortunately, a combination of kochia’s biology and herbicide resistant populations makes it a difficult weed to control.
Kochia has been known to be resistant to Group 2 herbicides for a number of years and more recently a segment of the population has now been proven to be glyphosate resistant as well. There has been a population identified in Southwest Saskatchewan that is resistant to Group 2 and 4 products. In addition to being a concern in pulse crops, glyphosate resistant kochia may become a problem in glyphosate tolerant canola acres in the future. This combined resistance, along with a widespread population and the tumble weed nature of kochia, creates significant concerns for control with the traditional practice of in-crop herbicide applications.
A four-year project looking at managing and controlling kochia with practices other than herbicides started in Saskatchewan in 2019 at the Western Applied Research Corporation at Scott and Wheatland Conservation Area at Swift Current. The project is funded through the Strategic Field Program. There were three trials within this project. Unfortunately, when you want kochia to grow it doesn’t always cooperate and the results from the 2019 growing season were not statistically significant. Issues with kochia establishment again in 2020 at the Scott location, resulted in this site no longer being part of the project. There were significant results at the Swift Current location during the 2020 growing season.
The first trial looked at herbicide layering in lentils. Herbicide applications included Valterra, Fierce, Focus, Heat and Edge harrowed in or Edge not harrowed in the fall before the lentil crop is seeded or a spring pre-seeding application with glyphosate. All treatments had a pre-seeding glyphosate application and an in-crop Solo application. The control treatment was no fall herbicide application, glyphosate applied in the spring before seeding and an in-crop Solo application. In 2020, kochia counts were conducted in all plots before seeding and later on in the growing season. The lowest counts at both timings were where Valterra was applied the fall before. The second lowest counts were where Fierce had been applied. For lentil yield, the plots that had Fierce applied in the previous fall and the plots that Valterra applied the previous fall had the highest yield. Lentils that only received a spring glyphosate application and an in-crop Solo application had the lowest yield. Please keep in mind that these results are from one year at one location. This trial was repeated in the fall of 2020 and will be repeated in the 2021 growing season.
The second trial looked at winter cereals in the crop rotation. In 2019, six plots were seeded to Liberty Link canola and six plots were seeded to RoundUp Ready canola. In the fall of 2019, winter wheat and fall rye were seeded into both types of canola stubble. In 2020, spring wheat was seeded into both types of canola stubble. In 2019, there were no significant differences between canola type for any of the measurements taken. In 2020, the highest average yield was in the plots seeded to fall rye, followed by spring wheat. The plots with winter wheat had the lowest average yields.
The third trial looked at seed bank reduction. Potential practices to reduce the seed return to the seed bank looked at are in-crop weed clipping, weed wiping with herbicide and destruction of weed seeds at harvest by crushing. Clipping occurred when kochia plants were 20 cm taller than lentils, at the first timing, 15 days later and at the first timing and 15 and 30 days later. Wiping treatments were herbicide application when kochia was at 80 per cent bolting, 21 days after bolting or a combination of the two. Instead of sourcing equipment to crush the weed seeds, 98 per cent weed control will be used in the final report. This value has been determined by research with the Harrington Seed Destructor in Western Canada.
In 2020, as expected, the no wiping or clipping treatment had the highest kochia counts. For wiping and clipping, all treatments resulted in reduced kochia populations except the clipping at two timings and clipping at three timings. For yield in 2020, yield was not increased with any of the treatments and some treatments, including clipping at two timings and clipping at three timings, resulted in lower yields. At harvest, all seeds were collected and lentil seed and weed seed were separated and weighed. For amount of kochia seed in the harvested sample, the clipping treatments at one, two and three timings had the lowest percentage.
More information will be available in the final report that is compiled after this project is completed.
If you have questions about weed control or other crop questions, contact your local crops extension specialist or call the Agriculture Knowledge Centre at 1-866-457-2377.