Freezing temperatures in spring can present problems for wheat and early-planted corn.
Last week’s cold spell saw overnight lows in the 20s and brought snowfall to the northern tier of Missouri counties. It created calls to University of Missouri Extension regarding potential damage to wheat and corn already in the fields.
This is not the first time for a spring freeze in the state. “The worst year in my recollection was in 2007, and on Easter Sunday, that year it was April 7,” says Greg Luce, University of Missouri Extension agronomist. “We had a severe freeze and, in fact, the temperatures got down to 20 degrees all the way down into southwest and southeast Missouri, so it was much colder. We did see some injury to wheat that year.”
No wheat damage
However, this year resembles the 2017 freeze. The state saw little injury that year as the crop was not far along. Luce says that wheat can tolerate extremely low temperatures. Ultimately, freeze damage depends on growth stage.
Across Missouri, wheat growth varies from very late tillering and early jointing in the north to near boot stage in the southwest. Sustained temperatures in the mid-20s can create injury at the boot stage.
For the most part, temperatures in southern counties remained in the 30s. For those in the north, the wheat crop was not as far along and tolerated the cold. “We’re probably in pretty good shape,” Luce says. But he, along with MU Extension agronomist Bill Wiebold, says freezing temperatures could pose a risk for early-season corn emergence.
Corn seed concerns
If the corn is up and out of the ground, it's tolerant of freezing temperatures, Wiebold explains. It is the seed planted in the ground that is susceptible to injury.
If farmers plant the corn and then experience cold weather, particularly cold rain with temperatures near the 40-degree mark, it can damage seed. He says what happens is the corn seed dropped in the ground is 8% moisture, so water will rush into that seed.
“If the water is cold, it damages parts of the cells; it will damage membranes, which will make the cells leaky,” Wiebold says. “The contents of seed will come out, and it can kill the young seedling.”
The first 48 hours are critical, Luce adds, as the seedling starts to germinate. After it has germinated and then it turns very cold, the seed can tolerate that well. “It is that initial intake of the water that is killing or disfiguring the seed," Luce says.
Plant corn when warm
Wiebold says corn farmers need to look at the risks associated with planting early in an unstable weather pattern. He conducted research on planting date's effect on corn emergence at MU’s Bradford Research Farm. The two-year study looked at six hybrids planted on different dates, starting at the end of March and lasting until the middle of June. He logged air temperature for that day.
Wiebold watched for individual corn plant emergence. “We're just talking about that little spike meeting up above the soil surface,” he says. “We would record that day.”
The research found that when the temperature is cold, it takes longer for that plant to emerge. The year he planted in the latter part of March, the temperatures were cold during the entire corn emergence process, between 46-47 degrees F.
“It took about 27 days for that corn to come up out of the ground,” Wiebold explains. When the crop was planted in mid-June, it was up and out of the ground in four days, which he says “is about as fast as corn or almost any crop will emerge.”
Wiebold notes that today’s seed treatments may improve emergence. Still, he was amazed that despite early-season planting into cold conditions, the mid-March corn still saw 71% emergence. However, waiting for warmer temperatures saw emergence at 93%.
The bottom line: Corn farmers who planted early and experienced cool, wet conditions should make a point to take stand counts this year to determine if replant is required this growing season.