By DENNIS BOWMAN
It is hard to believe that a year ago at this time corn planting was well underway. Little did we know that the dry and warm spring was going to extend into a very dry and hot summer.
One of the risks of early planting is frost damage. I have been told in the past that young corn plants are at relatively low risk from frost. Corn is a grass and it starts out with its growing point below ground. The young leaves expand from the growing point and push up and out into the sunlight.
As long as the growing point is undamaged, the plant will continue to produce new leaves. The lengthening stalk does not push the growing point above the soil surface until the V4 stage — four fully exposed leaves.
In 2012, mid-March-planted corn and an April 11 frost/freeze provided me with an opportunity to evaluate this in the field. Emerson Nafziger at the University of Illinois Crop Science Research and Education Center was conducting corn planting date studies, and his team took advantage of the good conditions last year to include very early planting. When the freeze hit, the corn planted in mid-March was at the V2-3 stage, where the growing point should still be about three-fourths of an inch below the ground surface.
On the morning of April 11, the Illinois State Water Survey network recorded temperatures of less than 28 degrees for about four hours. Soil moisture plays a big role in heat storage and heat retention. This is not something we normally even think about, but last year's dry soils did not provide much protection from the cold.
By the next day, it was obvious the damage had been severe. Nafziger and I decided it would be interesting to follow a group of these plants all the way through the season to evaluate what recovery might occur.
A week after the freeze, I rated all the plants in one of the plot rows. Fifty-five percent exhibited significant damage. Twenty-eight percent were almost or completely destroyed. We were very curious about whether these damaged plants would contribute to yield or just be "weeds."
I followed these plants throughout the season and took lots of pictures and measurements. At harvest, I collected ear samples representing the different levels of damage observed from the frost.
Plants with the lightest damage, less than one leaf of damage, averaged about 200 grams of grain per ear. Plants with up to two leaves damaged averaged 195 g per ear. Plants with more than two leaves damaged but with an undamaged green whorl averaged 182 g per ear. Plants where the whorl was heavily damaged but some green tissue was still visible averaged 93 g per ear. Of the plants that were totally wilted or had less than an eighth inch of green tissue visible, only one survived and developed an ear, weighing only 56 grams.
If you do find yourself looking at frosted corn plants, give them five to seven days to exhibit signs of regrowth. If the whorl is not showing significant signs of regrowth, don't include those plants in your population count as you evaluate replant options.
Maybe you have questions like: "In recent years, what is the latest calendar date for a 28-degree spring freeze in the Monticello area?" That and much more is available on the Midwest Regional Climate Center's new Frost and Freeze webpages at http://mrcc.isws.illinois.edu/cliwatch/NWS/. There are some great maps and data that illustrate the likelihood of killing temperatures.
Dennis Bowman is a crop systems educator for the University of Illinois Extension, Champaign County.