Corn silage values will be at record highs this fall, and the Upper Midwestern corn crop is maturing unevenly.

Those two facts make it more important than ever for growers to monitor the crop's drydown rate to ensure that it will be harvested within the recommended moisture range, says Joe Lauer, University of Wiscon-sin extension corn agronomist.

Lauer figures this year's corn silage will be worth $40-55/ton. That's for 150-bu/acre corn, which averages 7.5 bu of grain per ton of silage. At $5/bu (a rough estimate of the harvesttime corn price), silage is worth $37.50/ton just for the grain. Add at least $15-20/ton for the fertilizer value of the stover, Lauer advises.

“Growers need to consider that they're removing fertilizer and organic matter, and that's worth something,” he says. “And they need to keep that in mind as they negotiate a price.”

Even at this year's prices, corn silage is a good buy, he adds.

“It's a valuable commodity, but it's still one of the better things that can be fed to dairy cows.”

It's a valuable commodity only if it ferments and stores properly, so harvesting at the right moisture content for the storage structure is critically important. The recommended ranges are 65-70% moisture for bunkers, 60-65% for concrete stave silos, 60-70% for bags and 50-60% for oxygen-limiting silos.

To hit the moisture target, Lauer says growers should begin monitoring drydown when the crop reaches maturity. In Wisconsin, that's usually around Labor Day, but the crop is progressing a bit slower than normal this year and is more variable.

“Corn is all over the place, within fields and between fields, too,” says Lauer. “There's been so much cool weather that the crop is very uneven throughout the state.”

In addition, 5-10% of the acreage in southern Wisconsin had to be replanted because of flooding. That corn will mature late, and most of it will be chopped for silage.

Lauer recommends two or three moisture tests as the crop dries down, starting when a milk line forms at the top of the kernels. Multiple tests will tell you the daily drydown rate, so you can predict when the crop will be ready to harvest. On average, corn plants lose about 0.5% moisture per day in September, but that varies with weather and other factors.

Collect three or four plants that best represent the whole field and have the moisture measured, choosing plants from the same parts of the field for each test.

“You can measure it through a lab, in your oven or with a microwave. It doesn't really matter as long as you use the same way of doing it,” says Lauer. “The important thing is to know that relative change and let it be a guideline.”

He urges Wisconsin growers to take advantage of Silage Drydown Days, when they can take corn samples to central locations throughout the state for moisture testing. The results of those tests, posted on a Web site, can also be used to find out how the crop is progressing by region. Go to and click on Silage Drydown.