Chances are, there will be corn planting delays this spring. And you will start hearing scare talk about switching to earlier hybrids.

Tune it out.

Nature's on your side. Full-season corn hybrids can overcome considerable planting delays.

"There is evidence from both research and late-planting experience that growing degree unit (GDU) requirements for late-planted corn are usually less than for corn planted early," says University of Illinois agronomist Emerson Nafziger.

"In general, this decrease in GDU requirements is about five GDUs for each day of planting delay from late April to mid-June."

Nafziger explains that the reduction is probably due to the fact that grain-fill stops as temperatures decline late in the season. The crop reaches black layer earlier, although with somewhat less kernel fill and yield.

"This acts as a safety factor for late-planted corn," notes Nafziger. "It suggests that we not rush into changing to an earlier hybrid."

Purdue University agronomist Bob Nielsen and Ohio State University agronomist Peter Thomison, with former Purdue graduate students Greg Brown and Tony Halter, recently researched when to switch to earlier hybrids.

"Greg and Tony investigated the effects of delayed planting on the relationship between corn hybrid development and thermal time," Nielsen reports. "Their research was at 12 environments across Indiana and Ohio. The bottom line is that pollination and especially grain maturation occurs in less thermal time as planting is delayed."

Nielsen uses the term growing degree day (GDD) instead of GDU, and estimates the decrease in GDD requirements at about 6.5/day of delayed planting beyond May 1.

For example, a 2,700 GDD hybrid planted May 31 - 30 days beyond May 1 - will likely mature in 2,505 GDDs (30 x 6.5 = 195 fewer GDDs).

The conclusion, says Nielsen, is that there is no need to switch to an earlier hybrid anywhere in Indiana until early June plantings.

In Minnesota, there's an urgency to plant as soon as practical due to early frost dates in fall. But even if planting is delayed, growers should not be quick to switch from full-season hybrids, points out Dale Hicks, a University of Minnesota agronomist.

"Hang in there as long as possible," Hicks advises. "For Minnesota and most of the Corn Belt, a grower will come out ahead by planting a full-season hybrid later, even if it means lighter test weight. There will not be a major penalty."

What's more, Hicks notes, the best earlier hybrids often are sold out by the later planting dates.

Seed companies also urge growers to go slow on maturity switching.

"In the central Corn Belt, I would stay the course until at least the end of May with full-season hybrids," advises Pfister Hybrids' Rick Lohnes. "A farmer selects hybrids for certain reasons. Even if planted late, they will normally accomplish their purpose."

Pioneer agronomists estimate that switching too soon can result in a 1- to 2-bu/acre yield loss for each day earlier in the maturity of the replacement hybrid.

A Pioneer study in northern Indiana, northern Ohio and southern Michigan involved 110-day, 106-day and 103-day hybrids planted in early, mid- and late May. The 110-day hybrid averaged a 13-bu/acre better yield and $21/acre better income than the 103-day hybrid in the early May planting.

But even in the late May planting, the 110-day hybrid had a slight edge in yield and a comparable income to the other hybrids.

"Except in the northern-most states, hybrid maturity switches should not be considered until late May or early June," notes Steve Butzen, agronomy information specialist. "In northern states, recommendations vary from May 15 to May 25, depending on local conditions."