Identification is first step when keeping out new weeds

Weed watch | Several new weeds are creeping up to Ontario’s border

RIDGETOWN, Ont. — Producers are encouraged to hone up on their weed identification skills, and with good reason.

“If you misidentify something, you may not be able to control it, and some of the weeds are a huge problem outside of the Ontario because of herbicide resistance,” Dave Bilyea, a research technician at the University of Guelph’s Ridgetown Campus, told a Diagnostic Day held in Ridgetown July 9-10.

“We need to recognize the weeds before they become a problem.”

Palmer amaranth is a prime example in Ontario. It looks a lot like other pigweed species but there are physical distinctions, the most obvious being petioles that are as long as or longer than the leaves. Petiole refers to the stalk that attaches the leaf blade to the stem.

“It’s a weed we don’t want to see in Ontario, but it’s not far from the border. It’s in the furthest east county of Michigan,” Bilyea said.

“If you see these long-petioled pigweeds, you need to take action.”

Palmer amaranth was originally known as a desert species in U.S. Southwest.

It has migrated across the United States and has become a major concern because of its ability to develop herbicide resistance.

That includes resistance to glyphosate, ALS inhibitors and several other herbicide types, according to the International Survey of Herbicide Resistant Weeds.

All weed species relying on male and female plants for reproduction can readily develop resistance. Their offspring tend to be genetically diverse, and those that thrive are best adapted to their environment. Resistance to the chemicals develops quickly if that environment includes herbicides.

Along with pigweed species, Bilyea displayed other look-alike weeds including annual sowthistle, which looks like spiny sowthistle. It has developed resistance to ALS inhibitors in Alberta and Washington state.

Apple of Peru, an escaped ornamental, has become big problem next door to Ontario in Ohio. It was displayed next to its look-alike, eastern black nightshade.

Bristly foxtail, which has developed atrazine resistance in Spain, was displayed next to giant green foxtail, a common weed species in southwestern Ontario.

Biannual wormwood has become a concern because of the conversion of Ontario pastureland. It is similar in appearance to common ragweed and thrives once pastureland is tilled for row cropping.

Other look-alikes include:

  • lady thumb and pale smartweed
  • green pigweed and water hemp
  • goose grass, hairy crab grass and wooly cupgrass, an invasive from Asia

Hairy crabgrass has become a concern in Ontario corn fields because of its ability to thrive in low light conditions. Goosegrass is present in the province but not widespread.

Wooly cupgrass is found in Quebec but not Ontario. It’s viewed as a highly competitive problem In the U.S. Midwest.

“It’s listed as a prohibitive noxious weed in Ontario. I’ll have to burn this example when I’m done,” Bilyea said.

Water hemp is viewed as a potentially troublesome plant because, like Palmer amaranth, it’s highly adaptive. It’s now abundant in parts of southwestern Ontario.

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