Stop kochia from setting seed

By Shawn Senko

Kochia that survived pre-seed burnoff needs to be taken out before it drops seed later in the season. The big weeds can produce at least 15,000 seeds per plant – often many more – so letting them set seed and then spreading that seed with the combine can move a herbicide-resistant population across a field very quickly.

Kochia with resistance to both Group 2 and Group 9 herbicides is found all across the Prairies in big numbers. Agriculture and Agri-Food Canada weed scientists have also confirmed kochia populations with resistance to Group 4 and Group 14 herbicides.

Kochia Seedlings. PHOTO BY CLINT JURKE

The best practice is to control small kochia plants in the pre-seed window with a tank mix of effective herbicides. If kochia is still alive after crop emergence, growers have fewer options in canola fields.

The only in-crop herbicide option that works on Group-2 and Group-9 resistant kochia is an early application of Liberty on Liberty Link canola cultivars. Group-10 glufosinate in Liberty will control all resistant kochia populations as long as plants are not too large to kill at the time of spraying.

Roundup Ready, TruFlex and Clearfield systems based on Group-9 and Group-2 weed control are no longer effective on most kochia across the Prairies.

In all cases, scout after spraying. If kochia plants survived pre-seed burnoff and the first in-crop spray, use these other measures to stop them.

Physically remove kochia plants. Options include mowing areas where kochia is the dominant species and crop yield expectations are low. Hand weeding could be worthwhile in areas where individual resistant (or likely resistant) plants are present.

Use combine seed destroyers. Combine weed seed destroyers, the mechanical hammer mills that pulverize all seeds in the chaff, can effectively destroy at least 90 per cent of kochia seeds – as long as harvest is not delayed to the point where major seed drop has begun.

Apply Edge in the fall. This won’t stop seed set this year, but could be part of the solution in fields with a lot of resistant kochia. Group-3 ethalfluralin (Edge) applied in the fall on fields planned for canola the following year can help manage kochia resistant to glyphosate and other herbicides.

Canola growers with herbicide-resistant kochia may want to look at other long-term management strategies. They could seed kochia-infested areas to salt-tolerant perennial forage rather than continue to throw inputs at acres with no hope of profitability. They could diversify the crop rotation with early- and late-seeded crops, including winter cereals and forages that provide early season competition. If poor drainage is at the root of salinity problems, localized tile drainage may remediate low productivity areas where kochia tends to thrive. Farms that prefer Roundup Ready or TruFlex canola may want to consider cultivars with stacked systems – TruFlex and Liberty Link – to give them flexibility to manage herbicide-resistant kochia.

For more on this topic, please read “How to contain herbicide-resistant kochia” and “Integrated weed management: Best practices” in the Weeds section at canolawatch.org/fundamentals.

Shawn Senko is an agronomy specialist with the Canola Council of Canada. Email senkos@canolacouncil.org.