CORNversations with Kaur #5

With Wisconsin and the upper Midwest already experiencing cooler days and nights in late August and early September, a resounding question corn producers face is that will this help or hurt? Unfortunately, the short answer is, “it depends” and it hinges mostly on how long the cool temperatures prevail and whether we avoid an early frost. There are many scenarios that may be possible, it is critical to monitor the temperature changes and figure out the management plan accordingly.

Temperature Conditions (mid-August to Early-September)

The temperature drops have been significant since mid-August. Mean temperatures recorded at the Wisconet Arlington weather station have ranged between 52 to 70°F with minimum temperature being as low as 39°F (Figure 1). A comparison with the historical normal and 30-year averages, shows that the temperatures in the last three weeks have been consistently one to twelve degrees cooler (Figure 2).

Figure 1: Daily mean, maximum and minimum temperatures recorded at the Wisconet Arlington weather station from August 18, 2025, to September 5, 2025.

 

Figure 2: Departure of the observed temperatures from 30-year normals in Wisconsin from Mid-August to Early-September in degree Fahrenheit. Maps created from https://mrcc.purdue.edu/CLIMATE/

How will the low temperature conditions affect corn growth?

1. Slower heat-unit (GDD) accumulation = later maturity.
   Corn development is driven by growing degree days (GDDs). When temperatures fall, GDD accumulation is slower, resulting in delay for both whole-plant silage moisture targets and grain physiological maturity (black layer). If the night temperatures drop further, corn development almost comes to a standstill. This means that the plants may stay green, and the crop will reach harvest maturity later than expected.
2. In grain, a longer, cooler fill can pay, only if frost holds off.
   Assuming everything else remains steady, cooler grain-fill conditions tend to slow the rate of dry-matter deposition per day but extend the duration of grain fill. The elongation of this window often yields heavier kernels hence providing better yield potential than hot, hurried fills. Multiple agronomy syntheses and experiments tie greater kernel weight to a longer, less-stressed grain-fill period. In short, cool temperature period is a net positive unless an early frost truncates the finish.
3. …but an early frost before black layer is costly.
   Cool temperature may be beneficial but if leaves are killed due to frost before physiological maturity, kernel filling stops immediately resulting in lighter test weights and yield loss. The yield penalties are larger when the frost hits within dent.
4. Field dry-down slows in cool weather.
   Cool, short days reduce natural dry-down. As a rule of thumb, corn in September sheds about 5–1.0 percentage point moisture per day (lower in October). During the extended cool periods, the per-day drop is toward the low end of that range, meaning higher harvest moisture or added dryer time. This would imply higher drying costs and a higher budget for more propane if this pattern persists.
5. Silage quality: fiber often improves while starch is critical.
   Slower maturation can reduce lignification, increasing neutral detergent fiber digestibility (NDFD), which may improve the feed intake and milk yield. However, on the flip side, if cool weather pushes silage harvest late (or if frost intervenes), kernels may be less mature, reducing starch concentration and digestibility unless kernel processing is extremely efficient. Therefore, aiming to chop at ~65–70% whole-plant moisture (storage-structure dependent) and confirming with actual moisture tests, not just milk-line will help preventing any major losses.

Overall, cooler late-August and early-September weather in Wisconsin is a tricky situation. At one hand, it can extend grain fill, increase kernel weight, and improve fiber digestibility in silage. On the other, it delays maturity, heightens frost risk, and slows dry down creating management challenges.

Take homes:

• Monitor silage moisture with actual tests, not just milk-line stage.
• Stay alert to frost forecasts, especially during dent.
• Plan for higher grain harvest moisture and increased dryer fuel needs.
• Be flexible with harvest timing as the conditions can shift quickly.

Careful field monitoring and flexible harvest planning will be key to turning this weather pattern into an opportunity rather than a setback.

Literature Referred

Borreani, G., Tabacco, E., Schmidt, R. J., Holmes, B. J., & Muck, R. E. (2018). Silage review: Factors affecting dry matter and quality losses in silages. Journal of Dairy Science, 101(5), 3952–3979. https://doi.org/10.3168/jds.2017-13837

Iowa State University Extension and Outreach. (2017, September 13). Corn grain dry down in the field. Integrated Crop Management, Iowa State University. https://crops.extension.iastate.edu/cropnews/2017/09/corn-grain-dry-down-field-maturity-harvest

Nielsen, B. (2019, October 11). Frost or freeze damage to immature corn. Pest & Crop Newsletter. Purdue University Department of Entomology. Retrieved September 8, 2025. https://extension.entm.purdue.edu/newsletters/pestandcrop/article/frost-or-freeze-damage-to-immature-corn/

Thomison, P., & Lauer, J. (2019, October). Late-season frost effects on corn: Grain production (Adapted from Dr. J. Lauer, Univ. of Wisconsin). C.O.R.N. Newsletter, 33. The Ohio State University Agronomic Crops Network. https://agcrops.osu.edu/newsletter/corn-newsletter/2019-33/late-season-frost-effects-corn-grain-production-adapted-dr-j

Zhou, B., Yue, Y., Sun, X., Wang, X., Wang, Z., Ma, W., & Guo, T. (2017). Maize kernel weight responses to sowing date-associated variation in weather conditions. The Crop Journal, 5(1), 43–51. https://doi.org/10.1016/j.cj.2016.07.002

Note: This post is a part of blog series, CORNversations with Kaur. Please stay tuned for periodic updates!!