Take a closer look – it may be waterhemp

Waterhemp has set down roots across Ontario, from Essex and Lambton County, and reports indicate it may have migrated as far east as Quebec.

Controlling the invader poses several challenges for growers, says BASF agronomist Richard Anderson. The first problem is a high level of herbicide resistance. Some waterhemp is resistant to up to three herbicide modes of action – Group 2, 5, and 9 – explains Anderson who notes that 45 percent of the waterhemp plants that have been tested at the University of Guelph’s Ridgetown campus have shown resistance to all three groups.

Visually, waterhemp can easily be confused with a redroot pigweed.

“It’s becoming a concern because we don’t have a full complement of products to control it anymore because of the multiple stacked resistance,” says Anderson.

In this interview, Anderson tells RealAgriculture that the weed is also hard to identify, which makes it difficult to get a clear picture of its actual presence in the province. He explains that waterhemp can easily be confused with redroot pigweed.

Farmers who suspect they have waterhemp on their farm should use a hand lens to take a closer look, says Anderson. “The main difference that you need to look for when you pick up the weed is small hairs. If you can find hairs at the base of the leaf coming into the stem it’s a pigweed species… if you don’t find any hairs at all, it’s likely waterhemp.”

Anderson says the best control strategy for waterhemp is a good burndown combined with strong residual control. “The big problem with this weed is it has a very long germination period. Seeds can start germinating in May and continue into September.”

Crop canopy also plays a key role in controlling the invader. Anderson cautions growers to be careful when buying used combines. “Once a waterhemp plant passes through a combine it can have up to a quarter million seeds and those seeds will basically go everywhere in a combine,” he says.  “If you are looking at purchasing a combine from an area of the U.S. that may have waterhemp it would be a concern of mine. Be very careful with that because it may contain seeds that you don’t want to bring on to your farm.”

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