By Shannon Chant, P.Ag., Crops Extension Specialist, Swift Current
Driving around Saskatchewan in summer and fall, it is easy to find kochia in many parts of the province. Unfortunately, a combination of kochia's biology and herbicide resistant populations makes it a difficult weed to control. Acting early to address the issue starting in the spring to avoid plants establishment helps. The best start to a weed control plan is to know the enemy! Let's get started.
Kochia is an annual weed that has a type of photosynthesis known as C4. C4 plants, such as corn and kochia, produce energy more efficiently than C3 plants, like wheat and soybean. C4 plants are tolerant to hot, dry conditions like we had this summer.
Germination of kochia can occur under a range of conditions:
- Temperature: Seeds can germinate in soil temperatures as low as two to four degrees Celcius and as high as 40 degrees Celcius.
- Timing: In Western Canada, rapid germination occurs from mid-April to early-May, but can extend into June.
- Salinity: Seeds can germinate in saline soils, but germination may be slower.
- Seed depth: The optimal depth for emergence is from the soil surface to two centimetres deep.
- pH: Seeds are tolerant of extremes in pH.
- Longevity: Seeds are viable in the soil seedbank for one to two years.
Considerations for control with herbicides:
- Timing: Herbicides in the 2019 Guide to Crop Protection registered to control or suppress kochia have a range of application timings, from before kochia emergence to plants that are six inches high. Post-emergent herbicide application timing may miss the seeds that germinate well into the growing season.
- Herbicide resistance: Populations in Saskatchewan are typically resistant to Group 2 herbicides. Several fields with suspicious lines of kochia have been surveyed for glyphosate tolerance (Group 9) and resistant weeds were found. There has also been one field found that has a kochia population that is resistant to dicamba and fluroxypyr (Group 4 products). Two examples of herbicides with dicamba as the active ingredient are Banvel II and Oracle. Products that have fluroxypyr and 2,4-D as the active ingredients include Attain XC, OcTTain XL, Flurox-24 and Rush 24. Products that have fluroxypyr and MCPA as the active ingredients are Rush M and Trophy. 2,4-D and MCPA are also Group 4 herbicides.
- Plant characteristics: Herbicides can have trouble getting into the kochia plant because the leaves are covered in a soft, downy hair and have crystalline wax on the surface of the leaf. If a herbicide droplet gets stuck above the surface of the leaf, it won’t be absorbed into the plant. Surfactants can help overcome this for some products and should always be included if recommended. High temperatures can reduce the absorption or translocation of certain products. Some herbicides have a recommended minimum or maximum temperature for application. Spraying using these guidelines will help get the best results from the application.
Mechanical options can be used to help control kochia populations:
- Kochia is associated with no-till production systems; seedlings germinating from the seed bank can be four times higher in a no-till system than a system with tillage. This does not mean that farmers should change to a production system with more tillage over the long term, but, in patches or over the short term, tillage may help control populations. Tillage to bury kochia seeds below four centimetres after a year with a very high kochia population may reduce seedling emergence in the next year. In a greenhouse study, there was no emergence from seeds that were buried deeper than four centimetres.
- Mowing in ditches and other areas that do not have crops to control plants.
- Cutting a crop for green feed before kochia sets seed can be effective.
Kochia plants can produce 10,000 to 25,000 seeds per plant that are spread by tumble weeds rolling across fields and these seeds can easily establish in the spring. Any practice that can remove plants before seed set is an important part of control.
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