Soil Still Cool from Last Week’s Cold Snap

University of Missouri Extension specialists say corn planting in cool soils increases risk of poor emergence, weak stands and disease.

MU Extension agronomist Bill Wiebold’s research shows that planting too soon can slow emergence and reduce stand numbers.

After a week of temperatures in the 20’s and 30’s, Missouri farmers are going full-bore with corn planting, says MU Extension agronomist Greg Luce.

The April 20 USDA Crop Progress Report said that during the previous week, temperatures in Missouri averaged 43.5 degrees, 12.7 degrees below average, and hardly a warm welcome to corn planting. The state’s corn planting rose to 11 percent, 14 percentage points below the five-year average.

Wiebold’s two-year study on planting date's effect on corn emergence shows why planting into cool soils may not be the best strategy. Wiebold completed the study about 10 years ago, he says, so it does not consider the effect of today’s seed treatments.

Wiebold planted six hybrids of corn in test plots at MU’s Bradford Research Center on different dates between the end of March and the middle of June. He took counts of emerged plants. His data showed that corn took longer to emerge when air temperatures were low. Stand counts also dropped.
Corn planted in late March took as much as 27 days to emerge. Mid-June corn popped through in four days. Not only did cold-planted corn seed take longer to emerge, fewer plants emerged—71% compared to 93% on warmer days.

Luce cautions farmers to avoid shallow planting during cooler weather. Guidelines suggest a 2-inch depth for uniform emergence.

Wiebold says it is still early to talk about replant decisions, but farmers may want to review the MU Extension guide “Corn and Soybean Replant Decisions.”

The guide tells how to count and calculate stands, figure replant costs and compare yield potentials. The guide, available for free download at extension2.missouri.edu/g4091, provides worksheets to help growers make decisions for different regions of Missouri.

MU Extension plant pathologist Kaitlyn Bissonnette says corn planted in cool, wet soil also faces risk of Pythium root rot.

Conditions that delay seedling development and emergence can result in seed decay. Pythium species can cause the seed to rot before germinating or cause pre- or post-emergence damping off. Affected seeds may be discolored and soft and rot rapidly. Roots also may be discolored and break off easily when removed from the soil.