Corn is often described as a diva. It can thrive in the right conditions, but it does not like competition.

That’s especially evident when corn plants have to compete with weeds for moisture in dry conditions, as seen in Western Canada and the Northern Plains of the U.S. in 2021.

“There have been many studies done, including [Peter] Sikkema’s work from eastern Canada talking about a 50 per cent yield reduction from competition from weeds early in the season. We have that critical weed-free period where we want to protect the crop, up to the six-leaf stage in corn,” explains Harold Brown, technical services specialist with BASF in eastern Manitoba, in the video below.

The impact of early season weed control on corn in a drought is evident, both in plant size and yield potential, as Brown hosts us at a plot near Winkler, Man. for this Corn School episode.

Brown compares three herbicide treatments: an untreated check, corn that received pre-emerge glyphosate followed by an in-crop glyphosate application, and corn that received a pre-emerge residual/glyphosate tank mix followed by an in-crop glyphosate application.

“There are definite differences there, not just with the weed control…but you’ll also look at the effect on the corn,” he notes. “The treatment with the residual prior to emergence is the tallest, most robust, healthiest-looking corn here.”

Corn treated with a pre-emerge residual/glyphosate tank mix.

From a rotational perspective, corn also provides an opportunity to diversify chemistries used for weed control, adds Brown.

“This is an excellent opportunity because we have a wide range of herbicides you can use with a wide range of modes of action, and we talk about multiple modes of effective action, so you can utilize Groups 5, 14, 15, 27, along with your glyphosate,” he says.

“You can have multiple modes that are effective on some of those critical weeds, for example, glyphosate-resistant kochia, volunteer canola that is resistant to different groups, and other challenging weeds, such as waterhemp, which we recently found another population of in Manitoba, most of which is glyphosate-resistant. These are all weeds we need to stay ahead of.”

Check out the video below for more on the importance of early season weed control in a dry year with Harold Brown of BASF:

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