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Agronomic Crops Network

Ohio State University Extension


Ohio Crop Progress: Precipitation, Cool Weather, and Corn Dry Down

Shelled Corn

USDA Update
Corn harvest progress is slow but coming along (figure 1). On the last USDA report (10/16/2023), the average statewide temperature for the week ending on October 15 was 53 degrees (1 degree below normal). As far as precipitation, weather stations recorded an average of 0.65 inches (0.09 inches above average).

Eighty-six percent of corn was reported as mature, and 17 percent was reported as harvested. Harvest progress is 6 average points behind last year and 7 average points behind the 5-year average for this time of the year. The harvest moisture was reported at 26 percent.

Corn harvest progress in Ohio is in its early phases.


Corn Dry Down
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 midSeptember to late September). By early to midOctober, dry-down rates usually drop to 0.5 to 0.75% per day. Between late October to early November, field drydown 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.


On the other hand (outside of calendar dates), estimating drydown rates is possible by looking at Growing Degree Days (GDDs). Available literature has indicated that it generally takes about 30 GDDs to lower grain moisture each point from 30 to 25%. Drying from 25 to 20% requires about 45 GDDs per point of moisture loss. Note that these estimates are general and not hybrid specific. Hybrid’s requirements may vary. By this time of the year (October), and with the current weather, we are accumulating about 5 GDDs per day (assuming Tmax = 60F, Tmin = 50F).

Corn drydown is affected by precipitation and cold weather.

Past research in Ohio evaluating drydown provides insights on effects of weather conditions:

  • During warm & dry fall conditions, grain moisture loss per day ranged from 0.76 to 0.92%.
  • During cool & wet fall, grain moisture loss per day ranged from 0.32 to 0.35%.
  • Under warm & dry fall conditions, 24 to 29 GDDs were needed for each percentage point of moisture loss (that is 24 to 29 GDDs needed to decrease 1% of moisture).
  • Under cool & wet conditions, 20 to 22 GDDs were needed for each percentage point of moisture loss.  

Overall, grain moisture losses (drydown rates) are lower under cool & wet weather than under warm & dry weather. We need warm and dry days to gain harvest progress this year. The general recommendation is to harvest corn for dry grain storage at about 25% of field grain moisture. Allowing corn to dry (e.g., below 20%) while it stands in the field risks yield losses from stalk lodging, ear drops, ear rots, insect feeding, and other wildlife related causes. If one of those is a concern, consider harvesting those fields earlier (even if at higher moisture). The costs associated with drying grain (on the farm or at the elevator) should be also considered as part of making harvest decisions.


Thomison, P. 2017. Cool Weather and Corn Dry Down. C.O.R.N. Newsletter. Link: [accessed Oct. 16, 2023].

Nielsen, R.L. 2013. Field Drydown of Mature Corn Grain. Corny News Network, Purdue Univ. Link: [accessed Oct. 16, 2023].

Crop Observation and Recommendation Network

C.O.R.N. Newsletter is a summary of crop observations, related information, and appropriate recommendations for Ohio crop producers and industry. C.O.R.N. Newsletter is produced by the Ohio State University Extension Agronomy Team, state specialists at The Ohio State University and the Ohio Agricultural Research and Development Center (OARDC). C.O.R.N. Newsletter questions are directed to Extension and OARDC state specialists and associates at Ohio State.