MSU Extension Corn

The current corn growing season is gradually drawing to a close, and in the coming weeks, growers will begin corn harvest. Proper planning and timing of harvest is critical for multiple reasons. Harvesting corn too early can result in high moisture, increased drying costs (moisture price discount, drying fee and shrink factor), and decreased efficiency of harvest equipment. Harvesting too late can result in harvest losses due to lodging, reductions in grain quality, and delays in fall field work.

Weather conditions during the growing season drives corn development. The U.S. Department of Agriculture National Agricultural Statistics Service crop progress report from Sept. 15, 2025, indicated that 75% of corn fields in Michigan are at the dent stage with 15% already at physiological maturity. These numbers are about the same compared to the five-year average even though they lagged earlier in the season. Nonetheless, these numbers will change significantly, and most growers will see black layer formation in their fields over the next few weeks. Once black layer is formed, corn yield is already determined but additional time is needed for grain to dry down to optimal moisture levels for harvest to proceed.

Weather elements including air temperature, precipitation, solar radiation, humidity and wind greatly affect how kernels dry down in the field. Other factors such as ear angle, husk leaf senescence, husk leaf thickness and tightness, and husk leaf number also play significant roles.

Typically, kernel dry down is rapid when corn maturation coincides with dry and warm weather conditions but is slower under wet and cold conditions. Planting time and hybrid relative maturity (RM) have an impact on how quickly corn reaches maturity. Early planted corn hybrids generally mature earlier than late planted corn but that depends on the hybrid RM. Short and mid-maturity hybrids under early planting mostly mature before long maturity hybrids but under delayed planting, short, mid- and long maturity RMs mature about the same time due to a phenomenon referred to growing degree compression.

What we want growers to know

Our goal at Michigan State University is to help growers estimate the rate of kernel dry down after black layer formation to help facilitate harvest planning. We have provided data in this article for multiple corn hybrid maturities (89, 99, 109 RM) planted between early and late May across four years (2021, 2022, 2023 and 2024) from field trials conducted by the Cropping Systems Agronomy lab in East Lansing, Michigan. Additionally, temperature and precipitation data during the dry down period is included to provide some context on the impact on weather conditions during kernel dry down. The kernel dry down estimates provided will be most suitable for corn growers in central Michigan, but growers in other areas of the state can still use them as a general guide.

Kernel dry down patterns and significance

Figure 1 shows kernel dry down patterns for each year. In 2021, 2022 and 2024, the dry down patterns were similar, although the rates differed. In these years, all hybrids reached plateau moisture during the dry down period. Plateau moisture is the point beyond which no further drying is expected. Timing and value of plateau moisture is important because it can potentially affect storage quality, drying costs, and potential discounts at elevators.

In 2021, 2022 and 2024, plateau moisture for all hybrids planted in early May was 20% or lower, with some reaching as low as 14%. Under delayed planting, most hybrids still plateaued around 20%, except for the 109 RM in 2021, which plateaued at 23%. In contrast, the 2023 dry down pattern differed from the other years. Under early planting, only the 89 RM and 99 RM reached a plateau around 20% or greater while no hybrids reached plateau moisture when planting was delayed until late May. When kernels do not reach a plateau, additional dry down may still occur if weather conditions are favorable.

For early-planted hybrids in 2021, 2022 and 2024, plateau moisture occurred between Sept. 27 and Oct. 18, while late-planted hybrids plateaued between Oct. 16 and Nov. 4. Practically, this suggests that corn growers in central Michigan should aim to harvest early planted corn no later than Oct. 18. This timing is particularly important for growers intending to plant fall cover crops, as it helps ensure sufficient growing degree days for emergence and fall biomass accumulation.

Kernel dry down rate and weather impacts

Dry down rates differed numerically among hybrids and planting dates in all years (Table 1). The highest rate observed was 1% per day for the 89 RM hybrid planted in early May during the 2021 season. In 2021, 2022 and 2024, all hybrids dried at rates greater than 0.5% per day, except for the late-planted 109 RM, which averaged 0.34% per day. The average dry down rates across all hybrids and planting dates were 0.63, 0.73 and 0.72% per day in 2021, 2022 and 2024, respectively. In contrast, in 2023 only the 89 RM planted in early May exceeded 0.5% per day, while all other hybrids averaged 0.42% per day.

The higher dry down rates in 2021, 2022 and 2024 were primarily due to more favorable weather conditions (dry and warm) from September to November. While monthly temperatures from September to October were similar across all years (Fig. 2A), precipitation varied considerably (Fig. 2B). October 2023 was particularly wet, with rainfall on many days, and a total of 5 inches for the month. Although November 2023 was somewhat drier, daily maximum temperatures only reached 52 degrees Fahrenheit, and these cold conditions slowed subsequent kernel dry down rates.

As mentioned earlier, not all late planted hybrids in 2023 reached plateau moisture levels, but if November weather had been warmer, additional dry down would have been expected. The poor drying conditions likely resulted in higher harvest moisture in some fields in 2023.

Table 1. Kernel dry down rates, kernel moisture at black layer, and plateau moisture measured for two corn hybrids planted on two dates over four growing seasons in East Lansing, MI.

¹ Moisture at black layer is the kernel moisture content at the time of black layer (i.e., maximum yield).
² Moisture at plateau is the kernel moisture content beyond which significant additional dry down is not expected. Moisture did not plateau for 109 RM in early May planting and all hybrid RMs in late May planting.
Note: Data range for moisture at black layer and plateau is across hybrids and planting times. Corn is sold at a threshold of 15.5% moisture.

What number should you use to estimate dry down this year?

Weather plays an important role in field dry down of grain, resulting in differences in observed rates across years. For a more conservative estimate, Michigan State University Extension recommend growers to first use the average dry down rate across all four years to make an estimate for this year. This would mean a rate of 0.64% for early May plantings and 0.57% for late May plantings for typical hybrid maturity (99 RM) in central Michigan. If weather stays dry and warm, dry down rates will be more rapid. In that scenario, we will recommend growers to use the average dry down rates for 2021, 2022 and 2024 to estimate for this year. This would result in a rate of 0.70% for early May plantings and 0.61% for late May plantings for typical hybrid maturity (99 RM). Growers in lower southern Michigan could use slightly higher rates while those further north could use lower rates.