What, Me Worry?
While it doesn't do any good to worry about the immature corn crop as frost approaches, planning for various eventualities can help. So, what are those eventualities?
"Well, as usual, it depends," says Purdue corn expert Bob Nielsen. "Yield loss to fall frost damage depends on the severity of plant tissue death and grain fill stage at the time of frost."
Nielsen says a frost event that damages only corn plant leaves decreases yield potential less than a killing frost that obliterates the leaves, stalk, and husks.
"Considerable whole-plant damage can occur when temperatures fall below 32 degrees Fahrenheit for four to five hours or below 28 degrees for even a few minutes," he says. "Less-damaging frost also can occur at temperatures greater than 32 degrees when there are optimum conditions for rapid heat loss from the leaves, such as clear skies, low humidity, and no wind."
A killing frost prior to normal black layer formation will force black layer to develop prematurely. That results in incomplete grain fill and lightweight, chaffy grain. Grain moisture will be greater than 35 percent, requiring substantial field drydown before harvest.
Nielsen says yield losses from total plant death before maturity, or kernel black layer stage, are estimated to be 55 percent, 41 percent, and 12 percent for soft dough, full dent, and half-milk line stages of development, respectively.
Yield losses due to leaf death only before kernel black layer are estimated to be 35 percent, 27 percent, and 6 percent for soft dough, full dent, and half-milk line stages of development, respectively.
"Yield losses are lower when only leaves are killed because the stalk can remobilize carbohydrates from the stalk tissue to the developing ear for some time after frost damage occurs," Nielsen says.
Frosted grain will dry fairly normally after an initial delay in moisture loss, according to the Extension specialist.
Drying rates in the field typically drop to .5 to .75 percent per day in early October, so field-drying grain from 35 percent to 25 percent grain moisture content could require 2 to 3 weeks.