When is cold too cold for young corn?
A couple of pages on Mother Nature's calendar must have been out of order. In much of the Corn Belt, March was mostly dry and unseasonably warm. Now, April's turned wetter and cooler. Though the moisture's been welcome in a lot of areas, the dipping mercury isn't exactly just what the doctor ordered for young corn seedlings getting started on the land.
"The talk among some of the regulars is...that some of their neighbors who were feeling so smug a week ago about having planted so much corn so early are now feeling less certain of the wisdom of their actions in light of the recent cold temperatures and frost this week," says Purdue University Extension agronomist Bob Nielsen. "Should they be concerned about the health of their newly planted and, in a few cases, newly emerged crops? Well, we’ll know for certain come harvest time. But in the mean time, we can talk about possibilities."
The biggest threat to newly planted corn right now is a combination of cool soils and moisture called "imbibitional chilling." The time window for this to happen is relatively short -- about a day or 2 -- but because of the damage it can inflict on corn kernels yet to germinate, it is important to think about it when you're considering planting conditions.
"One of the risks that newly planted corn faces is that of imbibitional chilling injury due to cold soil temperatures during the initial 24 to 36 hours after seeding when the kernels imbibe water and begin the germination process," Nielsen says. "In response to the imbibition of water, kernels naturally swell or expand. If the cell tissues of the kernel are too cold, they become less elastic and may rupture during the swelling process. Symptoms of imbibitional chilling injury include swollen kernels that fail to germinate or arrested growth of the radicle root and/or coleoptile following the start of germination."
If you suspect this may have happened to some of your newly seeded corn, check for "corkscrew" mesocotyl formations or delayed or total failure in emergence. If you're looking to avoid imbibitional chilling, waiting until your soils are consistently above 50 degrees is a good way to stay safe.
"It is not clear how low soil temperatures need to be for imbibitional chilling or subsequent chilling injury to occur," Nielsen says. "Some sources simply implicate temperatures less than 50 degrees [Fahrenheit]. Others suggest the threshold soil temperature is 41."
If you're a few days out from planting, you can still get an idea of whether you've suffered damage from imbibitional chilling, according to Ohio State University Extension crop scientist Peter Thomison. Even if it has been a few days since you suspected seed may have been affected, it doesn't mean you're out of luck yet.
"Check plants about 5 days after the freezing injury occurred. New leaf tissue should be emerging from the whorl," Thomison says. "You can also observe the condition of the growing point by splitting seedlings lengthwise. If the growing point appears white to light yellow and firm several days after the frost, prognosis for recovery is good."