MANAGING MULTIPLE HERBICIDE-RESISTANT KOCHIA

Due to the prevalence of kochia resistance, it’s essential to be proactive and have an integrated weed management plan. There are specific BMPs related to managing herbicide resistance in kochia. This includes a combination of cultural, mechanical, biological and chemical control measures:

• Plan diverse crop rotations – Crop rotations that use a combination of early- and late-seeded crops will help keep kochia populations in check. Diversifying your crop rotation will also help ensure different herbicides are used each growing season. Incorporating winter cereals or forages that will compete with kochia can also reduce weed pressure for subsequent crops.
• Mitigate saline areas – Kochia thrives in saline areas that are unsuitable for crop production. Mitigate kochia growth in these areas by seeding them to saline-tolerant perennial forage.
• Increase crop competition – Increasing seeding density and using narrow row widths will help the crop better compete with kochia and reduce kochia seed production.
• Spray early – Take advantage of kochia’s early emergence to control flushes prior to crop emergence. Pre-seed tank mixes that combine a Group 9 herbicide and a pre-emergence broadleaf herbicide (with multiple effective modes of action) will provide multiple different selection pressures on the kochia population and help to mitigate resistance development.
• Scout fields early and often – Evaluate kochia control about two to three weeks after application. Look out for suspicious patches of kochia that may be resistant.
• Use in-crop herbicides following best practices – Mix and rotate herbicides — when possible, use at least two effective modes of action and always use labelled rates and timing. Herbicide layering with pre-emergent and post-emergent treatments are recommended. See crop specific recommendations in the next section.
• Use proper application techniques – To ensure optimum control, use recommended adjuvants and adjuvant rates, check your water source to ensure it is good quality, maintain adequate spray coverage by adjusting your water volume, and pay close attention to sprayer speed and boom height.
• Prevent plants from setting seed – It’s essential to manage any kochia patches to limit weed seeds from entering the soil seedbank. This can be accomplished by spot spraying, fall burndown herbicide applications, using targeted tillage, or mowing before seed set. Kochia seed viability tends to begin around mid-August.⁵ Patches can also be grazed or hand pulled.
• Consider cover crops – Where feasible, cover crops should be considered as an alternative to fallow. Fall-seeded cover crops can be effective at suppressing kochia density and biomass in the spring.
• Use harvest weed seed control equipment – Installing a weed seed mill on your combine can help to avoid kochia weed seeds from being spread across the field. Kochia is a good target for harvest weed seed control because its seed shatters very late in the season.

CROP-SPECIFIC CONSIDERATIONS

Kochia is problematic in many crops, and while resistance management best practices apply across the board, some are crop specific.

Cereals

Multiple herbicide-resistant kochia is a challenge for wheat producers as many in-crop herbicides for wheat have Group 2 and 4 active ingredients and Group 9 is often used for pre-/post-harvest kochia management and pre-seed burn-off. Tank-mixing a Group 9 herbicide with an additional broadleaf herbicide applied pre-seed will help to fight resistance and control early flushes. Group 4 and 9 herbicides can still be useful tools for kochia management in cereal crops, but growers should consider using multiple effective mode of action products and rotating or layering with other herbicide actives, including Groups 2, 3, 14 and 15.

Other cereal herbicides available for kochia control in-crop include: Groups 2, 5, 6 and 27. Since Group 4 and 9 kochia resistance is not on every farm, farmers who are currently employing good rotation practices should continue doing so, but can enhance their management by adding products or combinations that deliver multiple effective modes of action as well as other non-herbicide best management practices. This preserves all the tools for as long as possible.

Canola

It’s a recommended practice to seed canola into fields that showed good control of kochia in the previous year’s crop. A pre-seed tank mix that includes multiple modes of action will be effective. Pre-seed or pre-emergence options include Group 3, 6, 14 and 27 herbicides. In-crop options include Groups 9 and 10. Glufosinate-resistant canola varieties provide a good option for post-emergence kochia control. It is recommended to avoid growing glyphosate-resistant canola on fields infested with kochia.

Pulses

Controlling kochia prior to pulse crop emergence is vital as there are limited in-crop management options due to wide-spread Group 2 resistance. Tank-mixing a Group 9 herbicide for spring burn-off with a pre-emerge burndown and residual herbicide is recommended. Modes of action available for kochia control before growing pulses: Groups 3, 4, 6, 14 and 15. In-crop option include Groups 5 and 6.

Note for all crops: While using a pre- and post-emergence (herbicide layering) strategy is a recommended practice, growers need to be careful to not overuse Group 14 pre-herbicides.

Proactive resistance management leads to economic benefits

A recent study reported that the long-term return to a proactive resistance management strategy for kochia in Western Canada varies by farm but can be worth as much as $20 per acre per year over 10 years (Frisvold, G. unpublished). The study concluded that although resistance management practices to control herbicide-resistant kochia can add cost in the short-term, farmers gain significant economic benefits over the long-term.

This information is brought to you by CropLife Canada, Canola Council of Canada, Manitoba Crop Alliance, Prairie Oat Growers Association and SaskWheat.