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Harvesting Corn at Maturity Before Fall Frost

Categories: HARVEST, CORN

The question of, “Will my corn reach maturity before frost?” is soon to follow if planting is delayed. Although corn growing degree units (GDUs) required to reach maturity shortens with delayed planting, there can still be significant frost risk depending upon planting date, hybrid relative maturity and seasonal GDUs accumulated. 

Potential damage from fall frost prior to reaching maturity depends on the corn growth stage, how low temperature dropped below freezing and amount of time exposed to temps below freezing. This season, it’s particularly important to understand if your crop is on schedule to mature before frost. If it's not, it’s helpful to know potential impact and frost management practices.

Forecasting first frost
Estimating first killing frost with high accuracy is impossible. However, historical weather data can help calculate when frost typically occurs. The map below shows the median date of a 28°F killing frost based on 29 years of historical weather. Premature death can still occur at temperatures at or just above 32°F, depending on duration of exposure.


A healthy crop canopy can buffer overall temperature and protect the stalk and ear for continued normal development. Temperatures of 30–32°F for 1–2 hours often only results in leaf loss, while 4–5 hours typically kills the entire corn plant. Clear skies, low humidity and no air movement can also result in leaf temperatures dropping lower than actual air temperatures, potentially causing damage with temps slightly above freezing. This is observed more in low areas of fields, and usually only results in minor damage to upper leaves.

After estimating your local frost date, determine remaining days until typical occurrence. Use this to compare against the number of days still needed to reach physiological maturity.

Days to reach maturity
Depending on the current crop stage, a different number of days are required to reach maturity. Table 1 illustrates days remaining to reach black layer from different development stages. As a rule of thumb, it takes roughly 10 days to advance to each respective reproductive stage. From silking, it usually takes 55–60 days to reach physiological maturity. At maturity, a black layer forms at the base of the kernel, indicating it has achieved maximum dry matter accumulation and is no longer at frost risk. The kernel moisture content at black layer can range from 25–40%, but averages around 30%. 

Frost impact
Fall frost damage depends on crop stage and severity, as illustrated in Table 2. Potential yield loss is reduced by 50% or more in the time the milk line starts to form, until it reaches ½ milk line. If light frost occurred at ½ milk line, there may be no impact other than leaf damage. When frost occurs just prior to reaching black layer2, yield loss is minor.

In addition to frost-associated yield loss, test weights can fall below 52 lb/bu, and test weights less than 45 lb/bu may also reduce protein levels.3  When drying frost damaged corn, there are typically no gains in overall test weight, which is normally observed with undamaged grain. When corn death occurs prior to maturity, it often registers lower grain moisture values than actual due to surface drying. After drying, grain moisture content can deceptively read 1–2% lower than actual values. Along with reduced test weight, frost-damaged kernels are more susceptible to breakage and can be less digestible as feed corn. 

Grain harvest management
If harvesting frost-damaged corn for grain, consider the following practices to minimize further yield and quality loss:3

  • Adjust combine cylinder speed to reduce broken corn and foreign material that could cause storage mold problems, given grain will be more susceptible to breakage.
  • Dry frost-damaged grain at reduced air temperatures of less than 160°F, and store at 14% or less moisture.
  • Anticipate grain to be wetter than meter reading, due to surface drying.
  • Use slow cooling methods after gas drying.
  • Aerate stored grain frequently.
  • Expect shortened storage life of grain, and plan to haul grain to market before summer.

Silage management
In some cases, frost-damaged corn may be better used for silage. If frost occurred prior to dent, corn moisture will be too high for immediate cutting and require waiting until plant moisture reaches 70–75% before harvesting.2  If frost occurred in the dent stages, additional field drying may be necessary. Keep in mind if kernels are near ½ milk line, corn is at or close to ideal moisture for storage, and should be harvested immediately with little impact on quality or tonnage.

Contact your Golden Harvest Seed Advisor with questions or for additional agronomic insights.


  1. 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.
  2. Carter, P.R. and Hesterman, O.B. 1990. Handling corn damaged by autumn frost.  National Corn Handbook 57 April 1990. Michigan State University Cooperative Extension Service
  3. Charle R. Hurburgh, C.R., R. Elmore and P. Pedersen. 2007. Frost Damage to Corn and Soybean. PM 1635:
  4. Lauer, J. 2004. Guidelines for handling corn damaged by frost prior to grain maturity. Wisconsin Crop Manager 11 (23):148-149 August 26, 2004.  The University of Wisconsin Cooperative Extension.
  5. Stewart, G. 2009.Corn and cold September nights. Ontario Ministry of Agriculture, Food and Rural Affairs.
  6. University of Wisconsin. 2016. Corn Development.
  7. University of Wisconsin. 2014. Frost.                                                        

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