Milk line starting to appear at top of kernel
Grain Moisture: ~50-55%
~400 GDUs remaining to maturity
Yield loss from killing frost at this stage: ~ 35-40%
1/4 milk line
Grain Moisture: ~45-50%
~300 GDUs remaining to maturity
Yield loss from killing frost at this stage: ~ 25-30%
3/4 milk line
Grain Moisture: ~35-40%
~100 GDUs remaining to maturity
Yield loss from killing frost at this stage: ~ 5-6%
1/2 milk line
Grain Moisture: ~40-45%
~200 GDUs remaining to maturity
Yield loss from killing frost at this stage: ~ 12-15%
Black layer or no milk line
Grain Moisture: ~30-35%
0 GDUs remaining to maturity
Yield loss from killing frost at this stage = 0%
Figure 3. Kernel growth stages and approximate grain moisture, GDUs to maturity (black layer or no milk line), and yield loss from a hard, killing frost that stops kernel development.
Corteva Agriscience research indicates that it takes approximately 15 to 20 GDUs to lower grain moisture each point from 30% down to 25%, 20 to 25 GDUs per point of drydown from 25% to 22%, and 25 to 30 GDUs per point from 22% to 20% (Corteva Agriscience, unpublished). If a hard freeze occurs that stops corn development prior to maturity, these field drying rates may be affected. For example, corn frosted as early as the dough stage may require 4 to 9 extra days to reach the same harvest moisture as corn not frosted (Maier and Parsons, 1996).
Grain moisture at harvest affects the time and cost required to dry the grain to acceptable storage moisture levels, as well as grain quality. Wet grain can incur damage during combining, handling and drying. If grain quality is significantly reduced during harvest and drying, allowable storage time is also reduced, dockage may result, and losses of fines and broken kernels can trim bushels of saleable grain.
In seasons with delayed corn crop development, many growers will have to deal with wetter than normal grain at harvest. Several steps can be taken prior to harvest to make this job go more smoothly (Lauer 2009).
Combine Adjustments: Grain above 30% moisture can be difficult to remove from the cob and is easily cracked and damaged by over-threshing in the cylinder or rotor of the combine. Cylinder/rotor speed and concave clearance are the adjustments most critical to reduce grain damage and threshing losses. At high grain moisture growers may have to strike a balance between damaged grain and higher than normal grain loss from unshelled cobs.
With very wet grain, some ag engineers suggest beginning harvest with combine settings that would likely under-thresh a typical, lower moisture crop (Brook and Harrigan, 1997):
Properly drying very wet, lower quality corn is essential to avoid further quality reductions. Growers should screen lower quality grain prior to drying, using a rotary screen, gravity screen or perforated auger housing section. This will help prevent foreign material and broken kernel fragments (or “fines”) from blocking air flow essential to uniform grain drying and storage. Next, growers should plan to dry lower quality grain 1 or 2 points lower than the normal 14 to 15% often recommended for long-term storage. This is because of greater variations of moisture content within the grain mass and increased physical kernel damage and broken cobs, which could magnify mold problems.
According to extension specialists at North Dakota State University, energy efficiency is increased at maximum temperatures in high temperature drying systems, but these temperatures could scorch very wet or immature kernels. In addition, high temperature drying causes stress cracks in the kernel, which allows more breakage during handling and storage. The amount of stress cracking depends on initial grain moisture, rate of moisture removal, maximum grain temperature reached in the dryer, and rate of grain cooling. Therefore, drying temperatures need to be limited on corn of 25 to 30% moisture content (or higher).
With natural-air or low-temperature drying systems it will be difficult to adequately dry corn wetter than 26% grain moisture. The maximum moisture content for natural air dry-ing of corn is 21 percent using an airflow rate of at least one cubic foot per minute per bushel of corn (Hellevang, 2009).
Consider these investments to help manage harvest, drying, and storing wet, lower-quality grain:
The University of Wisconsin gives these additional grain drying tips (Lauer, 2009):
To reduce drying time and speed harvest, some growers have discussed partially drying and aerating corn while holding it for further drying after completion of harvest. This strategy requires skill and intensive management, especially with low-quality grain. For more tips on grain drying to maximize grain quality, see Appendix I.
Low test weight, lower quality grain is harder to store because it is breakage-prone and subject to mold and “hot spot” occurrence in the bin. Because the storage life of this grain may be only half that of normal corn at the same moisture content, consider selling this grain early rather than storing long-term.
To minimize storage problems, begin by screen-cleaning grain before binning to remove as much of the fine material, cob pieces and broken kernels as possible. After filling, “core” the bin (remove up to 10% of the total bin capacity) to eliminate broken kernels and fines that accumulate in the center. Next, level the grain in the bin to minimize moisture accumulation at the top of the grain. Finally, cool grain as soon as it is dry to within 10 degrees of air temperature, and continue to aerate for 10 to 14 days to ensure grain moisture “equilibrium” has been achieved.
Monitoring lower quality grain on a twice-monthly basis is essential to ensure that grain condition is maintained. For more tips on grain storage and monitoring procedures, see Appendix I and II.
When growers have fields of wet or immature corn in October, deciding when to start combining is difficult. Experiences during several late harvest years suggest that excessive delays may not be a good idea, for these reasons:
For these reasons, timely harvest is usually advantageous, even though drying costs may be increased.
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.
Brook, R. and T. Harrigan, 1997. Harvesting and handling high moisture, frost-damaged grain. Harvest Alert Fact Sheet #5. Field Crops Team, Michigan State University.
Hellevang, K. 2009. NDSU Extension Service to provide corn drying information at Big Iron. North Dakota State University Extension Service News Release.
Lauer, J. 2004. Guidelines for handling corn damaged by frost prior to grain maturity. In Issues in Agriculture. University of Wisconsin Extension.
Lauer, J. 2009. Will corn mature in 2009? Agronomy Advice – Field Crops 28:491-70. University of Wisconsin Extension.
Maier, D. and Parsons, S. 1996. Harvesting, drying, and storing frost-damaged corn and soybeans. Grain Quality Task Force Fact Sheet #27. Purdue University.
Thomison, P. 2011. Corn drydown: what to expect? Crop Observation and Recommendation Newsletter 2011:34. Ohio State University Extension.
The foregoing is provided for informational use only. Contact your Pioneer sales professional for information and suggestions specific to your operation. Product performance is variable and subject to any number of environmental, disease, and pest pressures. Individual results may vary. Pioneer® brand products are provided subject to the terms and conditions of purchase which are part of the labeling and purchase documents.
Operating Plenum Temp.2
Grain Temp. Maximum
Wet Milling Corn
1To maintain high capacity and grain quality, keep your grain dryer clean!
2Temperature ranges must be within 15-20 ºF anywhere within your plenum.
If ambient air temps fall below 40 F at night, then DO NOT operate cooling fans.
All stored grain should be checked every two weeks!