Manitoba soybeans OK after hard frost

Manitoba soybean growers dodged a bullet May 13 and 14 when much of southern Manitoba experienced a hard frost, because so few soybeans were out of the ground, according to Dennis Lange, a pulse crop specialist with the Manitoba Department of Agricuture.

“We can see temperatures as low as -2 C and they (soybeans) can tolerate it for short periods of time,” Lange said during the CropTalk Eastman webinar on Thursday. “That frost we had… was much colder (-7 C in some places), but fortunately most of the beans where under the soil surface and the ones that were poking up were just barely out of the ground so there really wasn’t much damage.”

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As of Thursday, Manitoba Agricultural Services Corporation (MASC) had received just one soybean reseeding claim as a result of that frost, said David Van Deynze, MASC’s manager of claim services.

MASC received 80 reseeding claims from farmers who believed their canola was damaged. However, as of last week, MASC wasn’t sure how many of the claims would result in farmers reseeding. MASC waits a few days before assessing the damage and in some cases damaged crops will recover.

Like with soybeans, there wasn’t a lot of canola out of the ground to freeze, Canola Council of Canada agronomist Angela Brackenreed said during the webinar.

Farmers should wait three to four days to assess both canola and soybeans after a frost. Although unlike cereal crops the growing points on canola and soybeans are above ground and therefore more susceptible to freezing temperatures. But both can lose their leaves and appear dead, but resume growing. Soybeans can start growing again from the terminal bud or from two auxiliary buds.

Determining how many plants survived by doing plant counts is key. Both soybeans and canola will branch out to compensate for lost plants. Depending on the time of year, soil moisture and the number of surviving plants it can be better to stick with the damaged crop instead of reseeding.

Seven to 10 plants per square foot is the ideal population for canola, but just two plants per square foot can produce a decent crop, Brackenreed said.

The recommended seeding rate for solid seeded soybeans is 200,000 per acre — 180,000 when seeding in rows 30 inches apart, Lange said.

“Based on seed survivability and germination you want to end up somewhere between 140,000 to 170,000 plants per acre,” he said. “(T)hat is where the best yield potential is.”

But even as few as 80,000 plants an acre can produce a decent yield, Lange said.

“I wouldn’t be working anything up at 80,000 plants per acre. I would make sure that field stays clean through the growing season — so keeping on top of your weeds.”

Lange recommends using a hula hoop 28.25 inches in diameter for easy calculations when doing plants counts. Multiply the number of plants inside the hoop to get a per acre count. Fifteen plants in the hoop means there are 150,000 plants per acre.

Unlike with smaller seed crops, deeper-planted soybeans will generally emerge so long as the soil isn’t compacted and there’s moisture for germination, but it will take longer, Lange said.

“Only go as deep as you need to go (to reach moisture),” he said, adding the ideal seeding depth is 0.75 to 1.25 inches.

“So if you have moisture at an inch and a half don’t go to two inches just because you want to make sure you are in deeper moisture,” Lange said. “You want to just get to some moisture.”

If seeding deep consider upping the seeding rate to offset potential higher seedling mortality, he added.

There’s also a risk some soybeans will just get enough moisture to start germination, but not enough to produce a seedling — a condition referred to as “dry seed.” But don’t panic if you find some dry seeds because they turn up in most fields, he said.

Usually farmers prefer to roll their soybeans, creating a smoother surface for easier harvesting in the fall, right after seeding, Lange said. However, because of dry soil some are waiting until they’re out of the ground. Lange recommends waiting until the soybeans are in the trifoliate stage.

“You don’t want to do it at the hook stage,” he said.

Rolling should only be done in the afternoon when it’s 23 to 26 C when the plants are their most pliable.

“Check for damage,” he said. “Make sure you don’t do a 160-acre test strip.

“Make sure that you are not snapping any hypocotyls. If you are, those plants are goners. You won’t have any regrowth from that.”

Look for damage to the hypocotyl when assessing frost damage in soybeans.

Look for damage to the hypocotyl when assessing frost damage in soybeans.
photo: Dennis Lange, Manitoba Department of Agriculture


About the author


Allan Dawson

Allan Dawson is a reporter with the Manitoba Co-operator based near Miami, Man. Covering agriculture since 1980, Dawson has spent most of his career with the Co-operator except for several years with Farmers’ Independent Weekly and before that a Morden-Winkler area radio station.



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