Drydown is defined as the rate at which moisture leaves the kernel after black layer has been achieved. Some factors that determine dry down are husk looseness, flowering, stay green and test weights. When husks loosen early, air is allowed to carry moisture away from the grain. Higher test weight hybrids, drydown slower because it is harder for moisture to leave high density grain with the harder seed caps. The more flinty the grain, that is smooth capped, the slower the drydown will be. Staygreen is also a factor in drydown, because the longer plant stays alive and healthy the slower the moisture will leave the kernels. What you give up in drydown with good staygreen hybrids, you gain in test weight because the longer the plant stays alive, the more completely they fill the grain. Flowering is a factor, because the sooner the plant flowers (pollinates) the sooner it can start filling the ear with grain and the longer the period of grain fill is before frost occurs.