An Agronomic Approach to Evaluating Early Frost Concerns for Corn
The overall cooler summer conditions have farmers and agronomists looking forward and wondering if corn fields will mature safely before the arrival of a killing fall freeze. A killing freeze is generally recognized as 28F for 5 or more minutes, or 32F for several (>4 hours). Frosts that occur at higher temperatures/shorter durations may damage leaves, but typically do not kill the whole plant.
Let’s take a look at a few ears of corn I pulled from some trials in Van Wert on August 27.
There are a few things to discuss in the photos. 402 and 404 were planted April 27, 2009, @ 30,000 seeds/acre. 409 and 410 were planted May 12, 2009 @ 34,000 seeds/acre. Note the 4/27/09 planted corn is filled nearly to the tip (especially 402), whereas the 5/12/09 corn is not. The comparison relevant to this article is that both the 4/27/09 and the 5/12/09 are at nearly the exact same growth stage visually (early dent). I did not shell the corn for moisture samples due to time constraints.
Peter Thomison, Ohio State University Corn Specialist, wrote an in-depth article in the August 24, 2009 CORN Newsletter. Peter answers the million dollar question.
Is your corn in early dent as of August 26? If so, it is likely that your corn will escape frost injury. Research indicates that corn needs about 510 GDDs to reach black layer from the early dent stage and except for Northeastern area of Ohio, most regions of the state will accumulate sufficient GDDs to escape frost injury.
Is your corn in early dough as of August 26? If so, it is not as clear cut as to whether your corn will escape frost injury. Corn at early dough in late August needs about 775 GDD to reach black layer based on the kernel development. There is no region of Ohio with that number of GDDs remaining until the 50% frost date. HOWEVER, late planted corn has shown the ability to adjust its maturity requirements. Corn planted in early June compared to early May requires 200 to 300 fewer GDDs to achieve physiological maturity. Therefore, this physiological “adjustment” may allow corn presently in the early dough stage to reach physiological maturity before frost. However the grain moisture of the corn will be much higher than is typical.
All three plots (101, 102, 103) were the same hybrid, planted on May 18, 2009. 101 is the untreated check, 102 is a late application of a fungicide at VT, and 103 is an early application of a fungicide at V5. The takeaway message is that there are no visual differences in maturity. Again, though, I did not shell the corn to determine moisture due to time constraints.
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