By Shannon Chant, PAg., Crops Extension Specialist, Swift Current
Kochia is showing up in fields in a lot of areas and the combination of kochia’s biology and herbicide resistance makes it a difficult weed to control.
Kochia biology:
- An annual weed;
- A C4 plant (produces sugars for a longer period of time during hot or dry conditions than C3; plants, like wheat and soybean);
- Seeds can germinate in soil temperatures from two to 40 C;
- Seeds are tolerant of extremes in pH;
- Rapid germination occurs from mid-April to early-May but can extend into June;
- Seeds can germinate in saline soils, but germination may be slower;
- The majority of seeds are viable in the soil seedbank for one to two years;
- Downy hair and crystalline wax on the surface of the leaves can reduce the effectiveness of herbicides if they prevent the herbicide droplets from entering the plant. Surfactants can be used to overcome this;
- Optimal depth for emergence is from the soil surface to two centimetres deep;
- Plants can produce 10,000 to 25,000 seeds per plant; and,
- Spreads by tumble weeds rolling across fields.
Herbicide resistant kochia is one of the herbicide resistant weeds surveyed for by Agriculture and Agri-Food Canada. In Saskatchewan, the surveys and other testing have found:
- All kochia is Group 2 resistant;
- Kochia resistant to Group 4 was confirmed in 2015;
- In 2019, 87 per cent of kochia surveyed was resistant to glyphosate (Group 9);
- In 2021, a kochia population resistant to saflufenacil (Group 14) was confirmed;
- Recently resistance to carfentrazone and sulfentrazone (Group 14) has been confirmed; and,
- Many kochia populations have resistance to multiple herbicide groups.
A kochia management project, proposed by Ministry of Agriculture specialists and funded by the Strategic Field Program, took place from 2019 to 2023 at Swift Current and Scott, Saskatchewan. The project looked at crop rotation, weed wiping with glyphosate, weed clipping and herbicide layering. Because of the dry conditions during this time, the germination of kochia was variable in some trials and data collected on kochia was impacted. The results of the project showed that:
- Lower kochia populations in peas when compared to lentils, possibly because the herbicide applied in peas had a mix of Group 2 and Group 6 active ingredients and the herbicide applied in lentils only had Group 2 active ingredients;
- Weed wiping and clipping above the lentil canopy reduced kochia populations that year and seed returned to the seed bank. These practices did not increase lentil yield and in some cases, lowered yields;
- Herbicide layering using a fall applied soil residual herbicide with a Group 14 active ingredient alone, or a herbicide that has Group 14 and Group 15 active ingredients followed by spring-applied glyphosate and an in-crop herbicide provided the best lentil yield and the best control of kochia in lentils;
- Having winter cereals in the rotation as the only control measure was not effective for reducing kochia populations; and,
Mechanical and cultural options should be used with herbicide applications to manage kochia populations. This can include:
- Diverse crop rotations with varying seeding dates and harvest dates;
- Increase crop competition with higher seeding density and/or narrower rows;
- Seed salt-tolerant perennial forages in areas with lots of kochia and no other plant growth;
- Using equipment to destroy weed seeds that end up in the combine;
- Tillage to control any lines of kochia that appear across fields. The operation should be done as soon as possible but the whole field does not need to be cultivated;
- Tillage to bury kochia seeds below four centimetres may reduce seedling emergence in the next year;
- Mowing in ditches and other areas that do not have crops to provide competition.
- Cut a crop for green feed before kochia sets seed;
- Pulling isolated, individual plants before they tumble can reduce the impact of resistance; and,
- If possible and economically feasible, tile drainage can remove some of the salts from the soil and allow less salt tolerant crops to be grown.
Integrated weed management with several different approaches is needed to deal with herbicide resistant kochia in the short and long term. Any practice that can remove plants before seed set is an important part of control and management.
For more information:
- Check out Saskatchewan Agriculture’s information on glyphosate resistant kochia;
- Visit Manage Resistance Now’s website Managing Herbicide-Resistant Kochia;
- See the 2023 Guide to Crop Protection;
- Contact the Crop Protection Laboratory about Herbicide Resistance Testing; or
- Contact your local crops extension specialist.