Cooler than normal temperatures and wetter than normal precipitation can impact corn drydown (figure 2). Once corn reaches physiological maturity (when kernels have obtained maximum dry weight and black layer is formed), it will dry approximately 0.75 to 1% per day during favorable drying weather (sunny and breezy) during the earlier part of the harvest season (from mid‑September to late September). By early to mid‑October, dry-down rates usually drop to 0.5 to 0.75% per day. Between late October to early November, field dry‑down rates drop to 0.25 to 0.5% per day. Finally, by mid November, drydown rate is stimated at about 0 to 0.25% per day. The later it gets, drying rates go lower and at times drying can be negligible.
An excerpt from: Ohio Crop Progress: Precipitation, Cool Weather, and Corn Dry Down