Soybean success: timing matters

A clean soybean field early in the season can make all the difference to your yield

Soybean Field

With some events, like a clearance sale or your own wedding, the need for punctuality is obvious. For tasks like controlling soybean weeds, the value of getting there early may be more subtle, but it’s no less important. As any successful grower can attest, when and how you address weed issues can be the difference between soybean success and a weedy mess.

Keeping it clean

“Weed control is especially important early in the growing season for Roundup Ready soybeans, and it’s important for yield as well,” said Dennis Lange, industry development specialist, pulses, with Manitoba Agriculture. “The cleaner you can keep the field early on, the better it will be in the long run.”

That advice is seconded by Ernie Sirski, a long-time farmer and a director with the Manitoba Pulse & Soybean Growers.

“In the early stages, soybeans are a very uncompetitive crop until they reach the third trifoliate,” said Sirski.

Not only do they have a limited ability to compete, but Sirski said there is research showing soybeans can actually sense when there are weeds nearby.

“The presence of weeds affects the way soybeans grow and affects the whole plant going forward; if you don’t have a clean field early on it impacts the plant at maturation.”

While there are a variety of weeds to watch for, wild buckwheat and volunteer canola are two of the biggest threats to soybeans.

“The majority of grasses are fairly easy to control, but wild buckwheat can be a challenge as it’s a harder weed to kill,” said Lange.

For that reason, most growers “go in twice and spray glyphosate at the first and third trifoliate, as it will give them the control they need.”

And as with many aspects of weed control, timing is everything.

“You don’t want to be going in too late,” said Lange. “Glyphosate is typically registered from the first trifoliate through to flowering. Once you have podding you shouldn’t spray anymore, as by that time the crop has a dense canopy and you could affect the yield.”

The need to act early also applies to the other leading soybean killer.

“Volunteer Roundup Ready canola can be a big problem and becomes a management strategy as you have to look closely at your rotation,” said Lange. “If there is any volunteer canola coming out you need to look at other products. Controlling volunteer canola early is crucial because if you wait until you see yellow flowers popping up, it’s too late; the yield has already been robbed.”

Be nice to the neighbours

Timing is critical, but there are other factors to consider.

“When spraying, consider what types of soybeans are growing on the adjacent farm so you don’t have drift problems. Are they Roundup Ready, conventional, Xtend Soybeans or another type that may not be Roundup Ready?”

If in doubt, Lange advised asking your neighbour what variety they’re growing while you keep one eye on the wind speed and direction.

“One of the biggest errors farmers make is waiting for all the weeds to come up before spraying,” said Lange. “You need to keep the field clean until the third trifoliate so you get the crop off and running; early control is critical. Spraying your first application of glyphosate early around the first trifoliate is ideal.”

As Sirski put it, “don’t let the weeds get ahead of the soybeans. In most cases, you’re better off spraying a day early than a day late.”

It also pays to expect the unexpected.

“Other than Round Up Ready Canola issues, soybean weed control is pretty straightforward IF you can get into the fields,” said Lange. “But sometimes you have the best laid plans and then get three inches of rain, so early weed control doesn’t get done.”

Scouting trip

No one is perfect, so some mistakes are inevitable; that’s okay, said Lange, as long as you learn from them.

“In addition to monitoring your fields as the crop is emerging to see if you have things like volunteer canola coming up, you should also scout after application to see what kind of weed control you achieved.”

While you’re scouting, watch for weed escapes and consider whether they’re due to missed applications or a sign of weed resistance issues.

Clearly, there’s a lot more to weed management for soybeans than “plant; spray; repeat”. In Sirski’s opinion, however, it’s worth the trouble.

“It’s exciting to see what soybeans have done in the last five years, especially in Western Canada. I also sit on the board of Soy Canada and we see the west as the main place for soybean growth in this country.”

Just in Manitoba, soybean acres have doubled from 800,000 to 1.6 million since 2012.

“The growth we see is amazing,” said Sirski, “and we see that growth continuing as earlier varieties are developed.”

So whether you’re weeding or wedding, late starts are best avoided. And if you happen to be the tardy groom, weeds will be the least of your worries.

About the author


Geoff Geoff Geddes is a freelance agriculture and business writer based in Edmonton. Find him online at or email [email protected]

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