CORNversations with Kaur #4

With more than 75% of the corn in Wisconsin already silking, harvest is just around the corner for many of the silage growers. The USDA crop progress report shows that more than 80% of the crop is under good to excellent condition, however, there are numerous factors such as silage moisture, dry down, other risk factors to consider for ensuring the right harvest decisions.

Understanding the silage dry down process

Peer-reviewed research shows that acceptable moisture range for harvesting silage corn is between 62% to 70% whole plant moisture. The moisture content also impacts ensiling method and efficiency for silage corn. Harvesting silage corn at 65 to 70% of whole plant moisture is consider the more optimum practice for upright silos. For bunkers and piles 63 to 68% is acceptable while for silo bags 60-65% is also workable.

In any case, harvesting silage corn that is too wet (>70% moisture), may lead to seepage and fermentation issues, poor packing, increased risk of acetic acid-based fermentation, growth of bacterium such as Clostridia resulting in rancid smelling silage which is lower in quality and livestock palatability. On the other hand, if silage corn is too dry (<60%), it may lead to issues like increased porosity, reduced packing efficiency, greater risk of kernel shatter and eventually poor fermentation.

It roughly takes about 42-48 days for most corn hybrids to reach from silking to mid-dent (R5.5) stage and be at 65-70% moisture content. It would also coincide roughly with the 50% kernel milk line (Figure 1); however, this relationship has become increasingly debatable with newer and stay green hybrids. Therefore, it becomes critical to sample the crop and directly measure % dry matter for the whole plant.

Furthermore, silage corn does not dry down at a steady rate. It is reported that after pollination, whole-plant moisture loss begins at a rate of 0.5 to 1.0% per day depending on following factors:

• Temperature and solar radiation
• Hybrid traits (stay-green vs. non-stay-green)
• Plant health and stress factors (foliar disease, drought etc.)

     

Figure 1: Corn ear showing kernels at half milk line at silage corn harvest at Arlington Research Station, UW-Madison. (Photos taken in September 2024)

In hot, and dry weather, fields can lose moisture very quickly, jumping from 70% to 60% in less than 10 days. Conversely, wet and humid conditions slow the process down, sometimes stalling it altogether. Therefore, it is important to track the moisture content and dry down to make timely harvest decisions. It could be tedious for the growers to have moisture meters at hand or have a quick access to a forage quality lab. But here is how growers can track their crop for moisture and dry down trends following few simple steps:

1. Start sampling at around ¼  milk line. Take plant samples at random spots from the field at the normal chopper length. About three to five plants from each representative field area (1/1000 of the acre) does the trick.
2. Chop the samples down so that you can draw a sub sample from it.
3. Weigh the sub sample.
4. Heat the sub sample in the microwave for five minutes.
5. Weight the sample again.
6. Reheat the sample in the microwave for another five minutes and weigh again.
7. Repeat the process (step 6) until the two consecutive weights are equal.
8. Subtract the final weight from #3 to estimate water weight in the sample.
9. Moisture content is then estimated by dividing the water weight to sample weight from #3.
10. Repeating the steps #1 to #9 weekly will give you an estimation of dry down rate and plan your harvest timing.

Pro tip: Monitor multiple areas in the fields, especially when hybrid RM or planting dates differ. Fields often vary more than expected. Growers can also collaborate with University of Wisconsin Extension dry down events being held in the fall to understand their crop moisture and dry down better. They can reach out to their local extension educators to learn more.

Risks to watch for in 2025 growing season

While the 2025 corn crop looks promising and is ahead of five-year averages in most part of the state, there are some variables to look out for a good havest strategy:

• Rapid dry down may occur in case abnormally high temperatures are observed following milk line development.
• Tar spot and other foliar stresses: There are few reports of low severity of tar spots in some southern counties of the state with few high risk areas in the northern part. Increased severity of these plant stresses may result in faster dry down.
• Ear rot infections may result in accumulation of toxic compounds in silage corn making it unfit for consumption by the livestock.
• Lingering smoke haze may temporarily reduce solar radiation and slow moisture dry down followed by a sudden moisture loss once the skies are clear.
• Lodging risks from late-season storms may accelerate moisture loss.

Final Tips on the go:

• Scout the fields periodically for any foliar or corn ear stresses and harvest fields that show higher levels of severity.
• Begin sampling for estimating moisture content early, especially if the smoke haze lingers.
• Prepare storage and ensiling systems in advance to avoid any packing delays.
• Log moisture and yield data for your hybrids to refine future decisions.

Literature Referred:

Abendroth, L.J., R.W. Elmore, M.J. Boyer, and S.K. Marlay. (2011). Corn growth and development. PMR1009. Iowa State University. https://www.researchgate.net/publication/280092215_In_Corn_Growth_and_Development

Guindon, C. (2023) How do I know when it’s time to harvest my corn for silage? Penn State Extension. Retrieved August 1, 2025, from https://extension.psu.edu/how-do-i-know-when-its-time-to-harvest-my-corn-for-silage

Kaur, H., Singh, M.P., Phillips, P., and Chilvers, M., 2023, Fungal infections in corn and management strategies. Spartan Dairy Newsletter Winter 2023. Vol 3, No. 1, 14-17. https://www.canr.msu.edu/news/fungal-infections-of-corn-and-management-strategies

Kung, L. Jr., Shaver, R. D., Grant, R. J., & Schmidt, R. J. (2018). Silage review: Interpretation of chemical, microbial, and organoleptic components of silages. Journal of Dairy Science, 101(5), 4020–4033. https://doi.org/10.3168/jds.2017-13909

Lauer, J. (2016). Harvesting corn silage. Corn Agronomy. University of Wisconsin-Madison, Agronomy Department. Retrieved August 4, 2025, from https://corn.agronomy.wisc.edu/Management/L059.aspx

Smith, D. (2025, July 22). Mid-season Wisconsin corn and soybean disease update: July 22, 2025. Badger Crop Network. https://badgercropnetwork.com/mid-season-wisconsin-corn-and-soybean-disease-update-july-22-2025/

Smith, D. (2025, July 25). Revisiting mycotoxins and silage: How to feed the dairy. Badger Crop Network. https://badgercropnetwork.com/revisiting-mycotoxins-and-silage-how-to-feed-the-dairy/

USDA National Agricultural Statistics Service. (2025, July 28). Wisconsin crop progress and condition report: Week ending July 28, 2025 (WI-CW3025). https://www.nass.usda.gov/Statistics_by_State/Wisconsin/Publications/Crop_Progress_&_Condition/2025/WI-Crop-Progress-07-28-25.pdf

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