It’s not the worst news, but it’s certainly not the news you want to hear for newly emerged corn and soybean plants: this weekend will feature low temperatures and frost risks. Soybeans tend to fare better than corn, but each has risk and will require scouting into next week.
“I’m not that concerned about a frost—both beans and corn will be able to handle your garden version of a frost,” says Ken Ferrie, Farm Journal Field Agronomist. “What really concerns me is a freeze for a prolonged period—we’re talking for more than one hour.”
This weekend’s temperature is expected to bottom for about four hours—putting corn and soybeans in the risk zone. Windspeeds are expected to drop to just 2 mph or 3 mph.
“If we have a freeze we tend to fare better—only the rows that are out there next to the grass on the headland tend to get hit,” Ferrie explains. “The grass stops the air from flowing through. Or, if you’re running your row cleaners too aggressive and you kind of plow a furrow and your beans are sitting down into that residue in the soil and they’re blocking the breeze, they are the one that tend to get hit.”
In addition, cloud cover can help offset prolonged low temperatures. In Ferrie’s area they’ll go from 40% coverage on Friday, to just 2% coverage during the freeze event.
What to expect from corn and soybeans
“On a scale of one to 10, with 10 being the worst we’re gonna call this a seven,” he says. “Best case scenario is the forecast is off by three or four degrees to the warm side and we’re back to worrying about normal farming practices. Worst case, the forecast of off three to four degrees to the lower side. All that corn that is up will be blown off at the ground and it’ll need to rebuild from there.”
In his area, corn is just at V1, and most corn doesn’t completely die from freeze events until about V4 when the growing point is out of the ground. Wetter soils will protect the growing point underground better than dry soils. Farmers in areas that need rain will need to dig plants to check for growing point damage.
“For you guys in Iowa who are dry and looking for water, this could be a problem if the corn sprouts are within half an inch of the surface,” Ferrie says. “Dry soil will allow the freeze to go deeper and you have the possibility of damaging the spike, causing the corn to leaf out underground.”
With soybeans, anything that hasn’t emerged will be okay. The emerged plants you’ll need to monitor for a few days to check for damage.
“The hypocotyl and cotyledon are the tough part, they can handle frost better than corn,” he says. “Any plants past the cotyledon stage will have leaf injury. If the first node survives it’s just cosmetic damage and we can rebuild the plant from there.”
Check for damage
In corn, you’ll know in less than 24 hours if it’s emerged and been hit. The corn will first turn dark green and then get pale. With soybeans you’ll know in the first 24 to 48 hours if you have damage, but it’ll take five to six days before you can assess how bad the damage is. Wait for new growth on the first node, if you have that the soybeans are in the clear.
Soybeans with PPO damage are more susceptible to low temperatures and will require closer monitoring.
Learn more from Ken Ferrie, including wheat tips, in this week’s special Boots in the Field Report: