Frost has damaged many late planted soybeans. The frost damage depends on the combination of how low the temperatures dropped and the stage of maturity of soybeans when the frost or multiple frost events occurred. Drilled or narrow rowed soybean may provide protection with a dense canopy compared to wider row spacing.

A killing frost (usually below 28°F for 4 hours) will kill leaves and stems. Moderate freeze will damage leaves but not kill plants. A light freeze will damage leaves only in the upper part of the soybean plant canopy.

After frost, it is best to wait two to three days to examine the crop. Waiting will provide you a more accurate assessment of the damage.

The stage of soybean maturity is important in understanding the potential impact of injury. Full seed stage, R-6, is the green bean stage and will have the most damage compared to more mature soybeans. Under these conditions, the soybean seed stops seed development, then will shrivel resulting in reduced yields.

Scout fields and start harvest at appropriate seed moisture. If you wait too long, then shattering is a possibility. However, be sure to wait until pods are mature in color before combining.

Once at the R-7 growth stage, yield reductions will be minor. Look for yellow pods which indicate physiological maturity. Split pods and look if beans have separated from the white membrane inside the pod. Pods such as these are physiological mature and fairly safe from frost injury.

Also, pods do not typically mature evenly. Pods on the lower part of the plant may be normally developed, whereas, those on top may be green beans. These wet beans are slow to dry and may have a range of dry to wet seeds in damaged fields. Drying may be a good practice to avoid spoilage. Some green beans in storage will turn yellow after 30 to 40 days of storage.

If you harvest and sell directly from the field, you will receive significant discounts when you market grain.

For further information, please contact Wayne Flanary, Field Specialist in Agronomy, at 816-279-1691, University of Missouri Extension.