The saying “If it ain’t broke, don’t fix it” doesn’t work for weeds. People promoting effective weed management have their own expression that is pretty much the exact opposite. Tammy Jones, weed specialist with Manitoba Agriculture, shared the catchphrase for a Canola Watch article back in June.
“If something is working, change it.”
Jones credited Australian Stephen Powles with this keep-weeds-on-their-toes quip.
Later that month, at canolaPALOOZA, I was hosting a podcast on integrated weed management (IWM) and we got into a discussion on prevention tips for herbicide-resistant weeds. I shared my version of the quote: “If it works, change it.”
On the spot I couldn’t remember who said it, but Breanne Tidemann, the Agriculture and Agri-Food Canada research scientist who participated in the podcast, bailed me out with an immediate response: “That’s a Stephen Powles quote.”
Powles is a professor at the University of Western Australia. I tracked him down and asked, by email, if the attribution is correct. Powles confirmed. He started using that line, or a slightly more Australian version, in the 1980s.
“In Australia, there used to be a well-known TV ad which stated, ‘When on a good thing, stick to it.’ For herbicides, I thus used ‘When on a good thing, don’t stick to it.’ This had really good resonance in Australia,” Powles says. “In North America, I have stated ‘When on a good thing, change it.’” (The way the phrase keeps morphing, it reminds me of an agronomy version of “telephone.” At least the meaning stays the same.)
He says the change-it approach will minimize the likelihood and impact of herbicide resistance. “Avoiding and minimizing resistance is all about diversity, and this starts with herbicide diversity,” he says.
Diversity comes from a continual shake up of herbicide groups and spray timing (spring, in-crop, fall) for each field. Use tank mixes with more than one “effective” herbicide group. Effective means the weeds aren’t resistant to it. Some populations of wild oats on the Prairies now have resistance to five herbicide groups, so the list of “effective” herbicides left is getting short. Kochia is resistant to Group 2 and now Group 9. There are many other resistant weeds and the list gets longer. Tidemann says Group 9-resistant palmer amaranth is rapidly moving north and is now along the Canadian border in North Dakota.
Other ways to add diversity are to use perennial crops or winter cereals in the rotation to increase competition at other times of year. Use narrow row spacing, shallow seeding and higher seeding rates to improve crop competition. Hand weeding (which is being done on a large scale in the U.S. because farmers are out of options) is a good technique for small patches of suspicious weeds.
Tidemann is researching combine weed-seed destroyers, including Australia’s Harrington Weed Destructor, and says the $85,000 to $100,000 after-market add-ons have a good place in weed management. “The herbicide-resistant weeds are the ones most likely to be there producing seed at harvest time,” she says.
Current WEEDit technology, which can see green weeds on brown soil and spot spray them on the fly, is the just the beginning of optical technology. Next-generation systems will spray weeds in-crop (green on green) and eventually identify specific weeds and give each species an effective spray mix.
Herbicide-tolerant canola has been an excellent tool for weed management. With Liberty Link and Roundup Ready stacks and TruFlex coming on the market in 2020, growers continue to see expanded options.
Weed competition, if uncontrolled, is a bigger threat to crop profitability than any insect or disease. Diverse approaches to weed management are not about the weeds per se; they are about profitable crop production in general. Powles, who has been encouraging these IWM practices for decades, says effective extension of these ideas has to be about the crop first.
“I don’t talk about IWM,” he says. “For growers, I know the emphasis is on the crop, therefore I talk about good farming, good cropping practices.”
Integrate integrated weed management into great farming.