CORN Newsletter: 2008-31, September 15, 2008

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C.O.R.N Newsletter 2008-31
September 15, 2008 - September 23, 2008

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


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According to the Ohio Agricultural Statistics Service (OASS), as of September 7, 63 percent of the state’s corn acreage was in the dent stage compared to 76 percent last year and 70 percent for the five-year average. This year’s delay in overall crop development is not surprising given the significant corn acreage planted late. In a May 27 report, the OASS estimated only 64 percent of the crop planted as of May 25 compared to 85 percent for last year and 78 percent for the past five-year average. Delays might have been greater this year if not for the drought stress that has hastened senescence and contributed to premature plant death in many fields. However, in areas of the state where corn is still green and/or in some stage of grain filling, what's the likelihood of frost damage?
Physiological maturity (when kernels have obtained maximum dry weight and black layer has formed) occurs 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.
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* (days)	Growing Degree Days To Maturity (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 September 16 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 GDD 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 GDD required to achieve black layer depending on the corn's developmental stage.

Table 2. Estimated GDDs remaining from Sept. 16 to the first fall frost for
Ohio.

Region	Avg. Frost Dates (50% Probability)	Estimated GDD Remaining From Sept 16 to Frost
Northwest	Oct 10 – Oct 20	204 – 254
North Central	Oct 10 – Oct 25	197 – 282
Northeast	Sept 30 – Oct 25	147 – 293
West Central	Oct 10 – Oct 15	225 – 282
Central	Oct 5 – Oct 15	233 – 294
East Central	Sept 30 – Oct 15	158 – 276
Southwest	Oct 10 – Oct 15	240 – 303
South Central	Oct 15 – Oct 20	315 – 367
Southeast	Oct 5 – Oct 15	164 – 227

If your corn is in the early dent stage as of Sept. 16, will it be safe from frost? Probably not, because it needs about 510 GDD to reach black layer based on the kernel development - GDD accumulation relationships indicated in Table 1. Table 2 indicates that there is no region of the state with that number of GDDs remaining until the 50% frost date.
If your corn is in the fully dented stage as of Sept. 9 will it be safe from frost? Table 1 indicates that it needs about 250 GDD to reach black layer from full dent stage and Table 2 indicates that most regions of the state will accumulate sufficient GDD to escape frost injury. The warm temperatures we've experienced recently are helping with heat unit accumulation. Moreover, 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.
Regions in which corn is at greatest risk to frost damage are those with late September/early October frost dates, especially sites in northeast and east central Ohio.
For more on this topic check out the following:
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

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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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