By Peter Thomison, Ohio State University Extension corn specialist
Recent wet, cool weather slowed drydown. By early to mid‑October, dry-down rates will usually drop to 1/2-3/4% 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 1/4-1/2% per day and by mid November, probably 0-1/4% 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 25-20% requires about 45 GDDs per point of moisture. In October, we accumulate about 5-10 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 0.76-0.92%. During a cool, wet fall, grain moisture loss per day ranged from 0.32-0.35%. Grain moisture losses based on GDDs ranged from 24-29 GDDs per percentage point of moisture (i.e., a loss of one percentage point of grain moisture per 24-29 GDDs) under warm dry fall conditions, whereas under cool wet fall conditions, moisture loss ranged from 20-22 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 24-25% grain moisture. Allowing corn to field dry below 20% risks yield losses from stalk lodging, ear rots, insect feeding damage 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.
To minimize losses for stalk lodging rot damage, avoid harvest delays. Identify fields that are at greatest risk for stalk lodging and harvest these fields first. Fields that experienced late season drought stress or extensive northern leaf blight or grey leaf spot would be prime candidates for early harvest. This is not the year to allow corn to dry in the field to 15% to save on drying costs.