Corn and soybean harvest has started across many parts of Iowa. Some areas of the state have swung between warm-dry and cool- wet weather within the last few days. With more rain in the forecast, a few producers may be wondering about how fast corn will dry down in the field in the coming weeks. Last fall we wrote an ICM News article highlighting the factors associated with corn grain dry down. In a nutshell: after the crop has reached maturity, the rate of grain dry down is largely driven by air temperature and relative humidity.
Corn grain dry down is typically not a concern during a warm, dry fall. Grain moisture often reaches near 15% by mid-October. However, with cool, wet weather it may take until early to mid-November to reach 15%.
Simulated dry down of hypothetical mid-September maturing crops during two contrasting weather years 1999 (warm-dry) and 2009 (cool-wet).
Measurements from our field experiments in Ames, Iowa show corn grain moisture to be between 23 and 30% as of September 20th. Assuming 34% grain moisture at black layer, early-September maturing corn should be getting close to 20% moisture, while mid-September maturing corn should be just below 29%. Our projections using historical weather data puts grain moisture in Ames between 18 and 22% by October 1 (Table 1 and Figure 2). Corn grain may not reach 15% moisture until the second week of October. In order to avoid harvest delays, we recommend making plans to dry corn post-harvest, especially if weather shifts back to cool and wet.
Anticipated corn grain moisture dry down for Ames Iowa.
Cooler, wetter weather conditions not only have implications on grain moisture but also grain quality. It should be expected that ear molds will increase and may lead to mycotoxins. Because of this, it is recommended that farmers scout fields and prioritize for early harvest those at highest risk of ear mold proliferation. This is extremely important for late planted, late maturing crops where attaining grain moisture near 15% in the field will become less likely as we move into late October and early November.