Silage Harvest Timing: Be Ready, By Adam Parker, Maizex Seeds


The 2023 corn crop season got off to a timely start across the country this spring. This will hopefully allow for a full growing season and provide producers with ideal quality and yield potential for their corn silage. With the timely planting, CHU accumulation was off to a good start. However, cool wet weather in the late summer has slowed the maturity process. Harvest is coming up quickly, and we need to monitor maturity and harvest corn silage at the right moisture content.

It is absolutely critical to get the silage harvest crop in the silo, bag, or bunker at the correct moisture content! When corn silage matures in the early part of the fall, it will dry faster than later in the fall. In the past, we have seen hot, dry days in early September take whole plant moisture content down by over 1% per day.

Determining the Correct Silage Moisture for Your Farm

The type of storage you use is the main factor that will determine the ideal moisture content to harvest your corn. Since you already have your storage in place, it is easy to match the ideal moisture content to your storage type.

The principle on proper silage storage is to pack the silage tight enough to remove as much of the oxygen as possible out of the silage. This helps reduce the amount of aerobic bacterial growth. The goal is to begin anaerobic fermentation as quickly as possible. Higher moisture silage will pack tighter; however, too much moisture can cause seepage from the silo. The taller the silo, the larger the bunker pit, and the heavier the packing tractor will allow you to move to the lower end of these moisture ranges, as the weight of the silage will help compact and displace air pockets. See the chart below to determine your ideal silage moisture content and some guidelines for moisture testing and drydown.

How to Determine Moisture Content of Your Standing Corn Silage

Milk-line Estimate

The milk-line is a physical line that marks the separation between solid starch and milky starch. It progresses from the top of the kernel at early dent down to the tip of the kernel where it will eventually black layer at maturity. This is a guideline that helps producers estimate whole plant moisture while in the field. There will be some variation on accuracy depending on weather and the individual hybrids. Note that ½ milk-line is approximately 65% moisture. This should only be used as a guideline. Actual sampling to determine moisture content is much more precise.

Chipper Test

This is a great way to get an accurate sample of your whole plant moisture. Take 6–12 representative stalks of corn from your silage field and process them through a woodchipper or silage harvester. Collect the sample and mix thoroughly so that the sample contains a homogenous blend of cob, leaf, and stalk. Use a Koster tester, microwave, or accredited lab to determine the moisture content of the silage. This needs to be done prior to harvesting (see milk-line targets above) to give an estimate of how long to wait until the corn has reached a desired moisture. For example, if the sample came back at 68% but the producer wants their silage to be 65%, then the corn will reach the desired moisture content approximately six days from the sample being taken (0.5% moisture loss per day on average).

Physical Appearance of the Corn Plants

Generally, the visual appearance of corn plants can provide some indication of moisture content. However, this is very subjective to each individual and varies from year to year. There are many different factors such as hybrid characteristics, leaf diseases, fertility, and environment that can alter the appearance of corn plants. Modern hybrids also have better stay-green traits that make them appear ‘wetter’ in the fall than they may actually be. The improved stay-green will allow the plant to stay alive longer while starch accumulates in the kernels and the cob moisture content decreases.

Factors Affecting Drydown in Corn Silage

Silage-specific hybrids are selected and bred for corn silage production. Generally, these hybrids will have a slower drydown curve to allow for a wider harvest window in the fall. This is generally due to kernel texture and the husk on the cob.  Some of these hybrids will have a longer and/or tighter husk, which slows down the grain content drydown.

Dual-purpose hybrids are generally grain-corn hybrids that have suitable characteristics for silage production. Because these hybrids are generally selected primarily for grain production, fast drydown is often sought after. For silage, this can narrow the ideal harvest window, which can prove challenging to target the correct harvest date. Producers using dual-purpose varieties need to be diligent to catch the rapid drydown curves of these hybrids at the right point.

Hybrid Maturity for Your Area

The drydown of a corn plant is a physiological process. Today, we have hybrids that range from 1950 CHU to 3300 CHU. It is important to know the maturity of your hybrids and how they will adapt to your area. Matching up maturity with planting date, maturity zone, and expected harvest date will all help you target the ideal moisture for harvesting your silage. Generally, the recommendation is to grow a silage variety that is 150–200 CHU longer than adapted grain corn for the area. If your silage hybrid tends to be close to adapted grain hybrids, you should expect to harvest early in the season. If you have an ultra-long maturity hybrid, you should expect to be toward the end of the season for harvesting.

Fungicides on Corn Silage

When fungicides have been applied to corn silage fields, this also needs to be considered when evaluating harvest date. Fungicides will tend to keep the corn plants healthier and alive longer, essentially delaying their maturity and drydown. Side-by-side comparisons of corn treated with fungicides and without will show that the treated corn will be approximately 3% wetter on average. During some harvest periods, this may add a week’s delay in harvest to get to the ideal moisture content.


As farmers, we are always at the mercy of the weather. The weather that we encounter each harvest season will greatly affect how fast your silage dries down. Hot, dry weather can greatly accelerate drydown to over 1% loss per day. And cool, wet weather can virtually stall drydown. On average, we tend to say that corn silage will drop 0.5% moisture per day or 3–4% per week.

Why It is Important to Have the Right Moisture Content

Final Thoughts

It is critical for you to know your ideal moisture content for corn silage—and even more important for you to harvest at your preferred moisture. As outlined above, there are several ways to determine the moisture content of your corn silage, with a physical test being the most accurate. Patience and attention to detail at harvest time will pay dividends as you feed through the next year.