Early planted corn growth has slowed with cool soil temperatures.

Corn takes about 100 to 120 growing degree days to emerge. Corn growing degree days (GDD) are calculated by subtracting the plant’s lower base or threshold temperature of 50 °F, that is 10 °C, from the average daily air temperature in °F or °C. Average daily air temperature is calculated by averaging the daily maximum and minimum air temperatures measured in any 24-hour period. This provides a way to determine how fast corn moves through growth stages. If there is no GDD above 50 then corn plant stays still and does not grow. With average air temperatures of 45 degrees F, research has shown in may take three to four weeks to emerge. Monitoring soil temperatures will provide insight into how fast corn will emerge.

Soil temperatures are measured at the University of Missouri weather stations located at the Buchanan County Extension office in St. Joseph and the Hundley-Whaley Research Center in Albany and track weather in real time. Graves Chapple Research Center weather is uploaded and then reported daily.

Cold soil temperatures can cause other corn emergence problems. Cold soil temperatures after planting within the first 24 to 48 hours can cause what is known as “inbibitional chilling.” Corn seed is typically at eight percent moisture and when seed is placed into the soil, it hydrates. If soils are cold, the cells are not as elastic and may break. This does not happen very often but when it does, it results in extremely poor corn stands.

Low soil temperatures can cause other corn emergence problems. Heavy, wet snow in northwest Missouri may lead a compacted soil surface which may restrict corn emergence. The coleoptile can rupture as it tries to push through dense soil surface and causing the leaves to unfurl under the soil surface. In addition, as soil temperatures swing up and down, this can result in the same type of injury. Corn may have corkscrewed mesocotyl.

The severity of any kind of corn emergence damage will require time. Scout fields a week to ten days after the injury event to determine if there is any injury to your fields. If soil temperatures warm, you may be able to assess fields earlier.

For more information, contact Wayne Flanary, Extension field specialist in agronomy at 816.279.1691.

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