Manitoba has its first cases of palmer amaranth, a weed well known for production hits in the U.S.
Manitoba Agriculture and Resource Development has confirmed two plants of the noxious weed in the RM of Dufferin as of the second-last week of September. Plants were found in a black bean field in the region.
“They have both been removed,” provincial weed specialist Kim Brown-Livingston said. “Completely — roots dug out of the soil, that type of thing.”
Why it matters: The two plants represent the first time the noxious weed has breached Manitoba.
The plants, one male and one female, were sampled for DNA testing by the Pest Surveillance Initiative (PSI) lab in Winnipeg for confirmation. Tests for herbicide resistance — something the weed has become infamous for in areas where palmer amaranth has gained a foothold — were sent to labs in Ontario, while testing is also being done in-province.
Results on herbicide resistance have not yet been reported.
Weed experts say news of the spread is unfortunate, but not surprising. In 2018, palmer amaranth was discovered in southern North Dakota, and is now reported in a long list of counties. With seeds able to travel through human traffic, wildlife, wind or waterways, weed specialists in Manitoba had braced for a possible case on this side of the border.
The weed, described as one of the largest weed problems in the U.S. due to its fast growth, large size and significant yield impact, can drop soybean production by 79 per cent, according to research out of Iowa State University. Other academic researchers commonly cite losses up to 91 per cent in crops like corn.
According to information from the North Dakota Department of Agriculture, the weed can grow between two and three inches a day in ideal conditions, topping out at six to eight feet tall. Seed production is prolific, with up to a million seeds being produced per plant in long seed heads.
An even greater danger, however, comes with the plant’s well-known tendency to shrug off herbicide.
It is for all of those reasons that Rich Zollinger, former extension weed scientist with North Dakota State University, described palmer amaranth as “the most pernicious, noxious, and serious weed threat that North Dakota farmers have ever faced.”
Pigweeds in general are difficult to differentiate, Brown-Livingston said. In particular, palmer amaranth has been noted for its similarity to water hemp, another nasty weed, although with a lower implication for yield hit. Both plants are described as smooth-stemmed, compared to its hairier cousins, like red-root pigweed.
Producers are told to look out for spikes that may appear at the end of leaves, as well as petiole matching or longer than the length of the leaves themselves, to help identify palmer amaranth. Leaves tend to be less elongated in shape than waterhemp, with the widest part at the base of the leaf.
Time to scout
Brown-Livingston is urging producers to scout their fields for the pest and send suspicious plants for testing.
“If you do see anything in those fields, please be careful and be vigilant and be watching for these weeds,” she said.
The weed specialist suggested producers keep spare garbage bags in the cab for removal and sample collection.
“If it is a pigweed, you don’t want it going through the combine,” she said. “You don’t want that seed spread because there’s hundreds of thousands of seeds on there. If there’s any kind of green tissue left on it, then it can be sent to the PSI lab for species identification.”
Tissue must be living in order for DNA to be extracted. The lab requires only a few grams for a valid test, she added.
Brown-Livingston noted that free testing is available for Manitoba Canola Growers Association members.
“I would strongly urge that if you’ve got material that still could be tested, get it tested, and then we’ve got some idea of what’s coming at us for next year,” she said.