To make sure your silage corn is at the right moisture level for ensiling, send a sample to a lab for testing, suggests Joe Lauer.

A moisture test is the only way to determine the whole-plant moisture content, and a lab test is likely to be more accurate than an on-farm test, says this University of Wisconsin corn agronomist.

Using the kernel milkline to indicate whole-plant moisture doesn't work with today's hybrids, according to Lauer.

For many years, farmers were told to chop corn at the kernel black layer stage for optimal silage fermentation. More recently, the Wisconsin recommendation was to start chopping at 50% milkline and finish by 25% milkline. But Lauer and his colleagues have found wide variations in plant moisture content at any kernel milkline stage.

“Every time we harvest a corn silage plot, we take two measurements: kernel milk and whole-plant moisture,” he reports. “So we've got a very large database — over 2,000 hybrids and fields — where we've measured both.”

At 50% kernel milkline, whole-plant moisture has ranged from 50% to 74%. Lauer figures kernel and whole-plant moisture no longer match up because breeders have added a stay-green trait to improve standability. Those hybrids' stems and leaves stay green after the ear is mature and drying down.

So he discourages farmers from using the kernel milkline to determine when to harvest. Instead, he recommends using the milkline as a “trigger” to begin monitoring whole-plant moisture, starting with a moisture test.

At the suggested trigger milkline levels (see table), corn plants probably will be too wet to start chopping. But they lose about 0.5% moisture per day in September. So the moisture test will help you predict when the crop will be ready.

“It'll get you closer than just using the milkline,” says the agronomist.

Several methods are available for determining forage moisture on-farm. Their results are faster and can be as accurate as lab test results. But few farmers have the time needed to follow proper procedures. That's why Lauer recommends having a lab do it.

Harvesting corn silage at the right moisture level is critical, he adds. A corn crop can generate more income when harvested for silage than for grain. That's if you choose the right hybrid, plant it on your best land, control weeds, etc. But if you do a good job of producing the crop, then your harvest timing is off, you'll lose the silage advantage.

“Everything you did before will be for naught if you don't do it right,” says Lauer.

Kernel Milk Triggers For Checking Plant Moisture

Type of Silo Recommended
Moisture Content
Kernel Milk
Horizontal bunkers 65 to 70% 80%
Silage bags 60 to 70% 80%
Upright concrete staves 60 to 65% 65%
Upright oxygen limiting 50 to 60% 40%