No one wants Palmer amaranth or waterhemp to become bigger weed worries in Manitoba, and there’s work focused on making sure that doesn’t happen, but local knowledge is still thin on the ground.
The two boogeymen of the weed realm were recent subjects of a successful resolution brought before the Keystone Agricultural Producers.
The motion, by ag diploma students from the University of Manitoba, seeks to have KAP lobby the provincial government for more supports into control strategies for the two noxious weeds.
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Why it matters: Palmer amaranth and waterhemp are the villains of weed horror stories in the U.S., thanks to their prolific seed production, yield damage and propensity for herbicide resistance.
Palmer amaranth has only been found twice in Manitoba, both times in the RM of Dufferin. Waterhemp has dug a wider footprint. As of 2023, the province reported it in 19 municipalities, mostly in the southeastern corner. Both weeds have reputations as yield killers, with the ability to spread rapidly and resist herbicides.
Kim Brown, Manitoba Agriculture’s weed specialist, said her department has been doing extension work on the two weeds since 2019, bringing in speakers from Ontario and North Dakota where the weeds are more widespread.
“Every single talk I’ve done this winter … every single time I talk about waterhemp,” Brown said. “We’re trying to reach as many farmers as we can.”
Her team keeps up with research on the two pigweeds from areas where they are a noted problem. However, Manitoba-specific research is limited.
That’s a good news-bad news scenario. Little research means no information rooted in Manitoba’s growing conditions, but the main reason control strategies are hard to test is because there are few of the problem weeds to test them on.
Provincial regulations require that Tier 1 noxious weeds be destroyed whenever found, and their in-field presence has been sporadic so far.
“We certainly are not going to be seeding any of this down and having plots in it,” Brown said.
Manitoba Agriculture’s prevention strategies have included municipal partnerships to improve drainage in affected areas so that seeds are not deposited by overland flooding. Farmers have been advised to clean equipment, especially if brought from the U.S., and to be cautious with cover crop mix seed. That has been one method of spread in the U.S., Brown said.
Chemical companies have been asked about future research and confirmation that strategies used in North Dakota will work in Manitoba.
Control
Enforcement of the Noxious Weeds Act is the purview of municipal governments, Brown added. Municipalities either form a weed district, with a weed board and weed supervisor, or appoint a weed inspector. The province is in touch with weed supervisors and inspectors in areas where waterhemp has been found.
More prevention could probably be done with more manpower, said Laura Schmidt, a production specialist with Manitoba Pulse and Soybean Growers.
“We need people to both monitor for this weed and to actually research the effective management strategies,” she said.
For instance, the province could benefit from a more frequent weed survey. The most recent province-wide survey results are from 2016 and the survey before that was done in 2002.
It’s hard to distinguish waterhemp and Palmer amaranth from more benign pigweeds, Schmidt added. More extension work might be needed to help producers identify the harmful plants.
“We need to be actively monitoring for these weeds and destroying them,” Schmidt said. “If you do spot a pigweed in your field, you want to be feeling that stem. If it’s smooth, we need to get your agronomist involved or get an accurate identification.”
Manitoba Canola Growers members have access to identification testing through that organization’s Pest Surveillance Initiative Lab. Schmidt also suggested contacting Brown if suspicious weeds are found.
Crop rotation strategies are also likely be important, Schmidt said. Waterhemp struggles to compete in dense crop stands, as opposed to field edges or row crops.
“We do have this kind of dependence on chemical control measures, which aren’t going to work well for these weeds over the long term. This is also going to require a bit of a fundamental change to our traditional weed management strategies.”
