With >70% of mature corn and harvest season just started it is time for a brief update on dry down and potential lodging issues post-recent storms. Cooler than normal temperatures and wetter than normal precipitation can impact corn drydown. We recently transitioned to cooler temperatures as well as ample precipitation in many parts of the state.
Corn Dry Down and Calendar Dates
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 mid‑September to late September). By early to mid‑October, dry-down rates usually drop to 0.5 to 0.75% per day. Between late October to early November, field dry‑down rates drop to 0.25 to 0.5% per day. Finally, by mid November, drydown rate is estimated at about 0 to 0.25% per day. The later it gets, drying rates go lower and at times drying can be negligible.
Corn Dry Down and Growing Degree Days
On the other hand (outside of calendar dates), estimating dry‑down 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; a hybrid’s requirements for actual drydown 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 Dry Down and Past Research in Ohio
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.
Summary
Overall, grain moisture losses (drydown rates) are lower under cool & wet weather than under warm & dry weather. We need warm and dry days to speed up corn harvest progress this year. The general recommendation is to harvest corn for dry grain storage at about 25% of field grain moisture or less. However, allowing corn to dry down (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 (in the farm or at the elevator) should be also considered as part of making harvest decisions.
For instance, recent storms raised questions and concerns for corn lodging. When lodging damage happens during the grain filling stages (R2 and later), flattened plants will likely remain that way through harvest. Most of the recent lodged corn was at the dent stage (R5) or phisiological maturity (R6). Yield losses from lodging are most severe when it occurs during pollination time or early reproductive stages (R2-R4). However, if corn becomes lodged during the later part of the season, ears might be non-harvestable if the damage is severe and no harvest accommodation can be made to pick ears from affected plants on a field (e.g. use of a reel, snout cones). Concerns may also be elevated with downed grain corn, as often the lodged plants will decrease air circulation and could lead to more ear disease formation and possible kernel sprouting.
To read more about these and other issues associated with strong storms, consult OSU Factsheets AC-1054 (https://ohioline.osu.edu/factsheet/ac-1054) and ANR-0151 (https://ohioline.osu.edu/factsheet/anr-0151).
References
Lindsey, A. J., Ortez, O. A., Thomison, P. R., Carter, P. R., Coulter, J. A., Roth, G. W., Carrijo, D. R., Quinn, D. J., & Licht, M. A. (2024). Severe storm damage and short-term weather stresses on corn: A review. Crop Science, 64, 1129–1166. https://doi.org/10.1002/csc2.21212
Thomison, P. 2017. Cool Weather and Corn Dry Down. C.O.R.N. Newsletter. Link: https://agcrops.osu.edu/newsletter/corn-newsletter/2017-30/cool-weather-and-corn-dry-down [accessed Oct. 16, 2023].
Nielsen, R.L. 2013. Field Drydown of Mature Corn Grain. Corny News Network, Purdue Univ. Link: http://www.kingcorn.org/news/timeless/GrainDrying.html [accessed Oct. 16, 2023].