Extension Corn Agronomist
Corn Maturity and Frost
Due in part to late planting and cool temperatures this year, much of Minnesota's corn crop will reach maturity (black layer) a little later than normal. In southern Minnesota, a lot of the corn is expected to reach maturity around September 20. In and around the Red River Valley, much of the corn will not reach maturity until the last week of September. As a result, there is a decent chance some corn will receive a frost before reaching maturity, especially in northern Minnesota.
Corn grain and silage characteristics at various stages of development and the effects of an early frost are summarized in Table 1. It should be noted that days to maturity are relatively consistent among hybrids. This is because hybrid maturity mainly influences the amount of time spend in vegetative development, with late maturing hybrids requiring more time from planting to tasseling than early maturing hybrids.
Table 1. Reductions in corn grain yield due to frost, along with corn grain and silage characteristics at various stages of development.
1 Derived from Behnken and Breitenbach, 2004
2 Derived from Hicks (2004), and Afuakwa and Crookston (1984)
3 Derived from and Lauer (1997), and Schmidt and Hallauer, 1966
4 Derived from Lauer, 1996
For those interested in assessing the developmental stage of corn and determining whether black layer has been reached, an excellent set of pictures have been compiled by Bob Nielsen at Purdue University, and are available at http://www.agry.purdue.edu/Ext/corn/news/timeless/GrainFill.html.
The extended forecast for both northern Minnesota (Crookston) and southern Minnesota (Redwood Falls) predicts daily low temperatures at or above 40⁰ F through September 18, with a low in the upper 30s predicted for September 19. Assuming that corn maturity would be reached around September 27 in northern Minnesota, a first frost on September 19 (8 days before maturity) would reduce grain yield by about 8-15% if it is a killing frost (leaves and stalk killed), or by 5-8% if it is a light frost (Table 1). A frost-free window through September 18 would extend the growing season almost long enough for corn maturity to be reached in much of southern Minnesota.
Another concern with delayed maturity is harvest moisture. This is because the rate of field drying slows as we move further into the fall (Table 2). Assuming that the crop reaches maturity before the frost, and that the average grain moisture at maturity is 31.5% (Table 1), one can come up with a rough estimate of grain moisture for various maturity and harvest dates (Tables 3 and 4). Harvest moisture values in Table 3 were estimated using the maximum dry-down rates from Table 2, while harvest moisture values in Table 4 were estimated using the average dry-down rates from Table 2.
Table 2. Field drying rates for corn in Minnesota.
|September 26-October 5|
|After October 31|
Table 3. Predicted grain moisture at harvest for various maturity and harvest dates, using the maximum dry-down rates in Table 2 and assuming 31.5% grain moisture at maturity.
Table 4. Predicted grain moisture at harvest for various maturity and harvest dates, using the average dry-down rates in Table 2 and assuming 31.5% grain moisture at maturity.
According to the estimates in Tables 3 and 4, corn that is expected mature on September 20 would be 19% moisture on October 5 if there is a rapid rate of drying, and 19% moisture on October 10 if there is an average rate of dry down. For corn that is expected to mature on September 28, these estimates indicate that harvest moisture will be 19.6% on October 20 if dry down is rapid, and 21.7% on October 25 if there is an average rate of drying.
Overall, it appears that corn harvest in Minnesota may be delayed a little later than normal to allow drying in the field. It also appears that much of the corn in Minnesota will need to be dried before storing. For corn in northern Minnesota that is not expected to mature until late September, these estimates indicate that the grain will be quite wet at harvest, and that significant drying will be needed.
Managing corn dryers and storage: http://www.bbe.umn.edu/Post-Harvest_Handling_of_Crops
Drying, handling, and storing wet and frost-damaged corn: http://www.extension.umn.edu/cropenews/2004/04MNCN22.htm
Harvesting frost-damaged corn for silage: http://www.extension.umn.edu/cropenews/2004/04MNCN23.htm
Afuakwa, J.J., and R.K. Crookston. 1984. Using the kernel milk line to visually monitor grain maturity in maize. Crop Sci. 24:687-691.
>Behnken, L., and F. Breitenbach. 2004. Minnesota SE region Ag newsletter. Available at http://www.extension.umn.edu/cropenews/RegNews/SESept242004.pdf (verified 10 Sep. 2008). Univ. of Minnesota, St. Paul.
Hicks, D.R. 2004. The corn crop - frost and maturity. Available at http://www.extension.umn.edu/cropenews/2004/04MNCN28.htm (verified 10 Sep. 2008). Univ. of Minnesota, St. Paul.
Lauer, J. 1997. Corn replant/late-plant decisions in Wisconsin. Available at http://corn.agronomy.wisc.edu/Publications/A3353.pdf (verified 10 Sep. 2008). Univ. of Wisconsin, Madison.
Lauer, J. 1996. Corn harvest in Wisconsin during cool growing conditions. Available at http://corn.agronomy.wisc.edu/AA/A009.html (verified 10 Sep. 2008). Univ. of Wisconsin, Madison.
Schmidt, J.L., and A.R. Hallauer. 1966. Estimating harvest date of corn in the field. Crop Sci. 6:227-231.