The Agronomists, Ep 98: Battling herbicide-resistant beasts with Drs. Charles Geddes and François Tardif
by RealAgriculture Agronomy Team
The advent of herbicide-resistant weeds was bad enough, but the expansion of type, area, and mode-of-action resistance has left nearly no field untouched across the all regions of Canada.
What can we do and how did we get here? To tackle that question, host Lyndsey Smith is joined by Dr. Charles Geddes, Agriculture and Agri-Food Canada at Lethbridge, and Dr. Francois Tardif, University of Guelph, to discuss resistance occurrence, development, and management.
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Summary:
We start with herbicide-resistance highlights of Tardif’s career — never assume!
Field-level testing must be utilized to be sure if resistance is present or not
Crop rotation is a key area of managing herbicide resistance
Need fall-seeded and perennials in the mix to get the full benefit
Increasing crop diversity decreases likelihood of resistant weeds
Lack of herbicide diversity also increases likelihood of resistant weeds
Broadleaf vs. grass weed resistance — is one worse than the other?
Weed-type and resistance rates is location specific
Resistant weed rankings, what has the greatest impact?
Controlling threats during off-season rotations, i.e. fleabane and fall rye
Cultivar and season effects
Clip from March 2020 Kelvin Heppner and Tammy Jones addressing herbicide-resistant kochia in Manitoba, Soothsaying?
Populations with low level resistance, overlooked in the past due to the expectation of some weeds being left over following herbicide application
Current state of herbicide-resistant kochia
Maps of Alta. over time showing progression of herbicide-resistant kochia
As time progresses larger proportions of weed populations are herbicide-resistant and more species are developing resistance
Managing herbicide-resistant populations, are we missing a step?
Seed destructors on combines, still not a perfect solution
Back to kochia!
Methodology has remained the same for detection of resistance but different results are clear: resistance is spreading
What contributes to spread of herbicide-resistant kochia
Combine cleaning: who’s job is it? Is custom work spreading weeds?
High rate vs. low rate application explanation
Cutting rate saves money but results in lower control rate of weeds, speeds resistance
Higher rate application will eliminate weeds with low grade resistance mechanisms
Cross pollinated vs. self pollinated, effects herbicide application rate decisions
Resistance building is on an exponential scale, one season there may be slight resistance and next year the resistance rates rapidly increase
Cross pollination vs. self pollination: how we get stacked resistance
Are grasses less resistant due to higher self pollination rates?
Other methods of control: Tillage and plowing, zappers!
You can’t spray your way our of resistance but multiple modes of effective action may stave off resistance development
Spot spraying, see and spray technologies, an exciting frontier but not the silver bullet
Now that herbicides are failing, there is opportunity for innovation in other fields
The next challenge is collaboration across disciplines to work out new methods of weed management
How long would it take for weeds to develop resistance to a novel MOA? A wide range
Rate of resistance development is driven by many factors
Can weeds “forget” resistance to herbicides? Removing selection pressure may result in loss of resistance, but sometimes for a completely different reason (plant fitness)
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