Farmers Evaluate Corn After Frost, Excess Moisture

May 12, 2010 07:00 PM

Rhonda Brooks, Farm Journal Technology & Special Projects Editor
Watch and wait are verbs that most farmers find challenging to put into practice.
Yet, that's exactly what agronomists are recommending farmers do, for the next three to five days, in order to evaluate the final impact from freezing temperatures that nipped corn and soybean crops in northern parts of the Corn Belt earlier this week.
Agronomists contend that because the growing points for soybeans are above ground, their survival rate, whether good or bad, is fairly straight-forward and easy to predict.

Farm Journal Associate Field Agronomist Missy Bauer and Farmer Leon Knirk count corn plants last Thursday in one of Knirk's fields near Quincy, Mich., to determine the final stand population.

But that's not true for corn. Because its growing point is below ground until the fifth- or sixth-leaf stage, corn often can survive and grow through light frost damage.
That's what Paul Kassel hopes will occur in northwest Iowa, where he serves as an Iowa State University Extension Field Agronomist.
"We'll have to see what kind of new leaf growth there is,” he says. "It may be this time next week (May 17) before we know how well the corn has recovered.”
Kevin Gale agrees.  Gale, an AgriGold Field Agronomist based in northern Illinois, says he is just beginning to check fields today and expects most of the corn in his area to survive since it was not beyond the V3 growth stage when the frost occurred.
He is unsure, though, about corn that was planted at depths of less than 1.75 inches. Shallow planting can contribute to greater levels of injury from frost or freezing temperatures, resulting in corn that is unlikely to survive.
In addition, Gale says young corn crops are sometimes vulnerable to wicking. The term refers to frost damage that occurs when extreme cold travels down the plant stem, below the soil surface, and into the growing point or crown. When the crown is damaged, corn has little to no chance of survival.
So far, Gale says he has seen no evidence of wicking this year in Illinois.
 "When it's 28 to 32 degrees for several hours at a time and freezing temperatures occur two or three nights in a row is when we tend to see wicking occur,” he explains.
Farmers can evaluate frost-damaged corn by digging up individual plants and splitting the stems to examine the growing point and the tissue just above the growing point, notes Jeff Coulter, University of Minnesota Extension Corn Agronomist.
"Healthy growing points will be firm and white to yellow in color,” writes Coulter in the May 1 issue of Minnesota Crop News. "If the growing point or plant tissue within 0.5 inches above the growing point is damaged, it will be watery and orange to brown in color, and the plant will not likely recover.”
Kassel says farmers can determine plant populations per acre by measuring out 1/1000 of an acre (this equals 17 feet, 5 inches in 30-inch rows) and then counting the number of healthy corn plants. If they count 32 healthy plants, that translates into an established population of 32,000 plants per acre. 
Assessing plant populations is a useful practice any year, but particularly after destructive weather when farmers need to determine plant survival rates. "It can help minimize the emotion in the decision-making process,” Kassel says.
He also encourages farmers to place flags by the rows of corn plants they evaluate, so they examine plants in the same areas of a field repeatedly to obtain consistent results.  
Yield loss that does occur from inclement weather is influenced by the reduction in plant population and the severity of plant damage, Coulter says. "In Minnesota, growers can expect yield losses of 5, 12, and 24% when the final plant population is reduced to 28,000, 22,000 and 16,000 plants per acre, respectively,” he reports.
On top of frost issues earlier this week, much of the Corn Belt is now experiencing cold, wet weather which can weaken already damaged plants. 
"Most seed these days is treated with a fungicide which helps prevent rot, but there's a lot of water out there,” says Ned Birkey, Michigan State University Extension Educator. "In fields with low areas, where the water has ponded, plants may not survive.”
Birkey says southeast Michigan fields have received more than 4 inches of rain in the past three weeks.
He adds that the excess rain means corn and soybean crops there will be subject to early-season root diseases, such as pythium and phytophthora.
That's all the more reason farmers need to do nothing to their corn crop for now, recommends Mike Toohill, Channel Agronomist, based in central Illinois. In his May 10 issue of Stalk Report, Toohill says doing nothing means no mowing, no side-dressing and no cultivating. He contends: "This down time gives damaged corn plants an opportunity to recoup without being burdened with additional stress.”

For More Information
Hard Freezes and Emerged Corn, Iowa State University
Frosty Corn, Toasted Plants, Purdue University

You can email Rhonda Brooks at

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