Recent wet, cool weather slowed dry-down.
By early to mid October, dry-down rates will usually drop to 50% to 75% per day (from rates of up to 1% per day in September when drying conditions are usually more favorable). By late October to early November, field dry-down rates will usually drop to 25% to 50% per day and by mid November, probably 0 to 25% per day. By late November, drying rates will be negligible.
Estimating dry-down rates can also be considered in terms of Growing Degree Days (GDDs). Generally, it takes 30 GDDs to lower grain moisture each point from 30% down to 25%. Drying from 25% to 20% requires about 45 GDDs per point of moisture. In October, we accumulate about 5 to 10 GDDs per day. However, note that the above estimates are based on generalizations, and it is likely that some hybrids vary from this pattern of drydown.
Past Ohio research evaluating corn drydown provides insight on effects of weather conditions on grain drying. During a warm, dry fall, grain moisture loss per day ranged from 0.76% to 0.92%. During a cool, wet fall, grain moisture loss per day ranged from 0.32% to 0.35%. Grain moisture losses based on GDDs ranged from 24 to 29 GDDs per percentage point of moisture (i.e., a loss of one percentage point of grain moisture per 24 to 29 GDDs) under warm dry fall conditions, whereas under cool wet fall conditions, moisture loss ranged from 20 to 22 GDDs. The number of GDDs associated with grain moisture loss was lower under cool, wet conditions than under warm, dry conditions.
Agronomists generally recommend that harvesting corn for dry grain storage should begin at about 24% to 25% grain moisture. Allowing corn to field dry below 20% risks yield losses from stalk lodging, ear rots, insect feeding and wildlife damage. This year growers should be prepared for localized root lodging and stalk lodging that may slow harvest and contribute to yield losses.