Drydown is the rate at which moisture leaves the kernel after black layer. Factors influencing drydown include husk looseness, test weight and staygreen. Drydown is hastened when the husk loosens early, allowing air to dry the grain. Northern and Eastern genetic types have looser husks. With husks loosening one week earlier in September, warmer grain-drying temperatures can make a dramatic difference in drying expense compared to mechanical grain drying.
Western hybrids tend to have a tighter husk that slows the rate of drydown. Drydown is slower in high-test-weight corn because it is more difficult for moisture to leave high-density grain with harder seed coats. Hard-grained Flint and Tropical types have a slower rate of drydown. Northern, Eastern and High Yield types have lower-test-weight grain and faster rates of drydown.
Consider stalk quality and drydown together. Strong staygreen hybrids tend to dry slower because they stay alive for a longer period of time. The longer they stay alive, the more completely they fill the grain and the better the test weight. However, staying alive longer and better test weight mean slower drying. Strong staygreen makes it possible to gain four weeks of stalk quality and superior test weight in exchange for giving up five days of grain drydown. This is usually a favorable cost-benefit proposition.