The mood uptown at the Downtowner Cafe is not good these days. Recent cool spells have further set back a corn crop that was already behind schedule because of the delayed planting this past spring (or was it early summer?). Reports from the crop scouts that some of the guys hire to walk fields for them is that very little of the corn has reached the dough stage of development, some is at the roasting ear stage, a little bit more is at the blister stage, and some hasn't even pollinated yet. (See my other article on Grain Fill Stages in corn in this issue of the P&C Newsletter.)
With all the concern about the risk of a killing fall frost damaging corn before it is mature (See my article my other article on fall frost risk assessment in this issue of the P&C Newsletter.), many growers are asking what potential yield loss could result. Well, as usual it depends. The following thoughts are paraphrased from an excellent publication on the topic, NCH-57, Handling Corn Damaged by Autumn Frost, available from your local Purdue Cooperative Extension Service office.
What Is A Killing Frost? A frost event that damages only the corn plants' leaves decreases yield potential less than a true killing frost that obliterates the leaves, stalk, and husks. Considerable whole plant damage can occur when temperatures fall below 32 degrees F for four to five hours or below 28 degrees for even a few minutes. Less damaging frost can also occur at temperatures greater than 32 degrees when conditions are optimum (clear skies, low humidity, no wind) for rapid heat loss from the leaves to the atmosphere (radiational cooling).
Potential Yield Losses. A killing frost prior to normal black layer formation will force the premature development of the kernel black layer, resulting in incomplete grain fill and lightweight, chaffy grain. Grain moisture content will be greater than 35 %, requiring substantial field drydown before harvest.
Yield losses from total plant death prior to kernel black layer are estimated to be 55, 41, and 12 % for soft dough, full dent, and half-milk line stages of development, respectively. Yield losses from death of leaves only (not stalk) prior to kernel black layer are estimated to be 35, 27, and 6 % for soft dough, full dent, and half-milk line stages of development, respectively. Yield losses are less when only leaves are killed because the surviving stalk can remobilize carbohydrates from the stalk tissue to the developing ear for some time after the damage occurs.
Grain Moisture Concerns. Frosted grain will dry fairly normally, after an initial delay in moisture loss. Remember that even if a corn crop barely reaches black layer before a killing frost occurs, the grain moisture content will still be 30 to 35 %. Some field drydown will need to occur before the corn can be safely harvested. Drying rates in the field typically drop to 1/2 to 3/4 percentage points per day in early October, so field-drying grain from 35 % to 25 % grain moisture content could require 2 to 3 additional weeks.
Return to the the Chat 'n Chew Cafe.
The Corn Growers Guidebook , a WWW resource for corn management systems in Indiana and the eastern CornBelt.
Purdue University Agronomy Extension WWW Home Page.
Purdue Agronomy On-Line! , Purdue's Agronomy Department WWW Home Page.