Linda Geist, University of Missouri Extension
COLUMBIA, Mo. – Corn growers should stick with their normal hybrid maturities rather than switch to earlier-season maturities through the end of May, says a University of Missouri Extension corn specialist.
Frequent, excessive rainfall has delayed planting statewide. But Brent Myers advises growers to hold steady.
"A shortened growing season does not necessarily translate into a need for a lower maturity rating," he said, noting that research has shown that late-planted corn matures in fewer calendar days than early-planted corn of the same hybrid.
"Relative maturity ratings apply to corn adapted or selected for a specific region that is planted ‘on time,’" he said.
The timing of corn growth and development is mainly controlled by the temperature. Corn needs to accumulate a minimum number of "thermal units" across the growing season to reach physiological maturity.
"But there is a big difference between the effective thermal units in a typical late-April day than in a typical late-May day," Myers said. "Later-planted corn is developing in a different thermal environment than its relative maturity was designed for."
In a study published in 2002, researchers in Indiana and Ohio planted corn on three dates between late April and June. The later-planted corn, both short- and long-season hybrids, matured an average of nine days before earlier-planted corn.
Myers said that corn’s yield potential has begun to decline slightly because of planting delays, but opportunity remains for a good growing season.
After the end of May, yields begin to drop by 20 percent, and by 40 percent by mid-June. When corn planting is delayed past mid-June, corn growers may want to consider other crops, Myers said. But until then, stick with plans to plant corn.
For more information, see the article "Corn Maturity Ratings and Delayed Planting," by Brent Myers and William Wiebold. It is available online at ipm.missouri.edu/ipcm.