Brrr. Those soybeans got cold
Abnormally cold temperatures across several states May 9-10 have soybean farmers concerned about the status of their young crop.
Where temperatures dropped to 32°F. – or below – agronomists recommend waiting several days before seeing whether the plants have freeze damage. From Colorado east to Ohio and north into Canada, temperatures on May 10 ranged from 6°F. to 20°F. cooler than the average for the past 69 years, according to National Weather Service data.
With farmers planting soybeans earlier than typical because of good planting conditions, they worry that soybeans may have been nipped by frost. It’s a legitimate concern, says Emily Huber, field agronomist for Corteva Agriscience, near Peoria, Illinois.
“Soybeans are a little more at risk than corn because the growing point is above ground as soon as they pop out of the ground,” she says.
Soybeans just emerging should be less vulnerable than those plants that have the first trifoliate leaves showing, says Brad Mason, field agronomist for Corteva Agriscience in western Illinois.
Where soybeans are just beginning to emerge, the cotyledons should help insulate against cold. “These are filled with a buffer solution, a combination of wax and fat, that helps insulate the plant,” Mason explains.
If the main stem were to get injured, there are two other growing points next to the cotyledon. Those can grow up and become one or two main stems, Huber adds.
Soybeans can tolerate cold – to a degree. “If the temperature gets below 28°F. for three or four hours, the crop is more susceptible,” she adds.
As hard as it is to wait to see if there’s damage, growers will have to wait several days to see if the soybeans will grow out of it.
“Don’t jump the gun and begin replanting a day or two after the freeze,” Mason says.
Huber agrees. “We have to have time for the symptoms to show. And then, wait for the crop to recover and evaluate which plants do recover. If we go out earlier, we won’t see a lot of growth,” Huber says. “Patience is the name of the game.”
What to watch
There are clues to look out for in your soybean fields, the agronomists agree.
- High residue cover. “Tillage is the first thing I look at. Conventional tillage allows soil to warm up faster and dry out. That provides a benefit when we see cold temperatures, especially when it’s been warm the day before,” Mason says. No-till fields don’t have the benefit of a dark surface to absorb heat, but they do retain moisture better, and that can insulate the soybean seedlings.
- Low organic matter. Coarse soils, which typically have low organic matter, don’t radiate nearly as much heat, Mason says.
- Lower-lying areas. Valleys, or low areas in upland fields, tend to get colder than higher elevations. Watch these areas for potential soybean damage, Huber says.