CORN Newsletter: 2009-28, August 24, 2009

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C.O.R.N Newsletter 2009-28
August 24, 2009 - August 31, 2009

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Assessing the Risk of Frost Injury to Late Maturing Corn
by Peter Thomison, Allen Geyer


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Visual inspection of kernel development stages in research plots at the Western Agricultural Research Station near S.Charleston this past Friday (8-21-09), revealed that corn planted in late April and early May was in the dent stage, corn planted about May 20 early dough, whereas corn planted in early June was in the milk stage; at the Northwest Agricultural Research Station near Custar, corn planted the second week of May was in the dough stage whereas corn planted the first week June was in the late blister stage. These observations are fairly consistent with what OSU Extension Ag Educators are reporting across the state. This year’s delay in corn development is not surprising given the record low temperatures experienced in July and reduced accumulation of heat units. What’s the likelihood that this slower than normal crop development will result in frost damage?

Physiological maturity (when kernels have achieved maximum dry weight and black layer has formed) occurs about 7 to 8 weeks after silking. At physiological maturity (kernel moisture approximately 30-35%), frosts have little or no effect on the yield potential of the corn crop. Results from Indiana and Ohio research on corn development with delayed planting suggest that corn planted in mid- to late-June in Indiana and Ohio will typically mature from 68 to 71 days after silking The number of days from silking to maturity increases with later-planted corn primarily because growing degree day (GDD) accumulation per day decreases dramatically toward late summer and early fall and so it simply requires more calendar days for a late-silking crop to accumulate a minimum number of GDDs to reach physiological maturity (Nielsen, 2008).

Table 1 shows the average number of calendar days and growing degree days (GDD) required to reach physiological maturity after silking. With average daily high and low temperatures of 80 and 60 degrees F, 20 GDD accumulate each day. At these temperatures, 65 days from silking to maturity are required (1300 divided by 20). With "cooler" high and low temperatures of 75 and 55 degrees, only 15 GDD accumulate daily, requiring more than 87 days from early August silking to maturity.

Table 1. Relationship between kernel growth stage and development.

Stage	Calendar Days To Maturity*	Growing Degree Days To Maturity
	(days)	(GDD)
Silk	65	1300
Blister	52	1040
Late Milk/Early Dough	39	775
Early Dent	25	510
Fully Dented	12	250

* Based on average daily high and low temperatures of 80 and 60 degrees F, respectively, during grain fill

Source: National Corn Handbook. Chapter 40. Growing Season Characteristics and Requirements in the Corn Belt. R.E. Nield and J.E. Newman, 1986.

How many GDD can be expected from now until an average date of a killing frost? To answer this question (approximately), estimate the expected GDD accumulation from August 26 until the average frost date (50% probability) for different regions of the state (Table 2). These GDD expectations are based on 30-year historical normals reported by the OASS. The growing degree day accumulation was calculated using the 86/50 cutoff, base 50 method.

If you want to determine the "youngest stage of corn development" that can safely reach black layer before the average frost date at a given weather station, use the information in Table 2 on remaining GDDs in conjunction with Table 1 which indicates GDD requirement to reach black layer at various stages of grain fill. Compare "GDD remaining" for the site with the GDDs required to achieve black layer depending on the corn's developmental stage.

Table 2. Estimated GDDs remaining from August 26 to the first fall frost for Ohio.

Region	Average Frost Dates (50% Probability)	Estimated GDD Remaining From August 26 to Fall Frost
Northwest	Oct 10 – Oct 20	538 – 622
North Central	Oct 10 – Oct 25	523 – 608
Northeast	Sept 30 – Oct 25	472 – 618
West Central	Oct 10 – Oct 15	577 – 634
Central	Oct 5 – Oct 15	527 – 653
East Central	Sept 30 – Oct 15	507 – 625
Southwest	Oct 10 – Oct 15	673 – 719
South Central	Oct 15 – Oct 20	693 – 745
Southeast	Oct 5 – Oct 15	511 - 634

If your corn is in the early dent stage as of Aug.26 will it be safe from frost? Table 1 indicates that it needs about 510 GDDs to reach black layer from the early dent stage and Table 2 indicates that except for northern areas, most regions of the state will accumulate sufficient GDDs to escape frost injury.

If your corn is in early dough stage as of Aug. 26 will it be safe from frost? Maybe, it needs about 775 GDD to reach black layer based on the kernel development - GDD accumulation relationships indicated in Table 1. While Table 2 indicates no region of the state with that number of GDDs remaining until the 50% frost date, 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.

Although written with 2008 Indiana growing conditions in mind, the following article by Dr. Bob Nielsen, corn extension agronomist at Purdue University, provides a good perspective on assessing the likelihood of frost damage to late corn plantings.

Nielsen, R.L. (Bob). 2008. Late Planted Corn: Enough Time to Mature? Corny News Network, Purdue Univ. [On-line]. Available at http://www.kingcorn.org/news/articles.08/DaysAfterSilk-0729.html
[URL verified 8/26/09].

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C.O.R.N. is a summary of crop observations, related information, and appropriate recommendations for Ohio Crop Producers and Industry. C.O.R.N. is produced by the Ohio State University Extension Agronomy Team, State Specialists at The Ohio State University and Ohio Agricultural Research and Development Center. C.O.R.N. Questions are directed to State Specialists, Extension Associates, and Agents associated with Ohio State University Extension and the Ohio Agricultural Research and Development Center at The Ohio State University.

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Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Keith L. Smith, Director, Ohio State University Extension.

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