As corn kernels mature, corn grain moisture is lost through plant mechanics (cob and ear shank), through the exposed ear tip, and some through the husk leaves. These rates of loss vary among hybrids, and can be a relative measure of maturity for seed companies.

It is often said that hybrids from a company that are rated one day apart in maturity will differ by 0.5% in grain harvest moisture if planted and harvested together.

Many factors influence how fast a particular hybrid dries down, explains Clarke McGrath, ISU Extension area agronomist at Harlan, Iowa. McGrath, who is manager of ISU's Corn and Soybean Initiative, provides the following list.

"Research shows that field dry down is pretty steady, and linear, from 40% down to around 20%, then tails off to very little field drying after that in most years," says McGrath. "The rate of dry down is closely tied to air temperatures."

The other big factor is when your field hits the "black layer" stage, or physiological maturity. Fields that hit maturity in early September will generally dry faster than those that hit black layer mid to late September.

In years with the earlier planting and quicker heat unit accumulation, you may have better-than-average field dry-down rates. Numbers tossed around indicate early maturing corn (around Sept 1) will average around eight-tenths of a percent of moisture loss per day, while the corn maturing around Sept 20 will average about fourth-tenths of a percent loss per day. Here are some other common rules of thumb - looking at dry down by time frame rather than maturity date.

How long will the corn stand? "This question is debated all the time, with good points on both sides," says McGrath. "The stress from early season cold, wet weather coupled with the hot, dry weather during grain fill may set us up for stalk rot."

This year in early September, he saw a lot of plants that had the beginnings of some stalk problems. It seems to vary by area and by hybrid. He says to keep in mind that plants with small ears will probably stand better than the fields with better yields and larger ears.

"We have this factor in our favor this year - plant maturity has advanced and the drydown rates are high, so we may be able to get the crop out of the field earlier," notes McGrath. "Scout your cornfields now. If 10% to 15% or more of the plants have soft stalks or collapse when pushed on, get that field taken out quickly.