By Scout Nelson
Many farmers across southern Minnesota planted corn and soybean crops early this season because of strong field conditions during mid to late April. However, frost warnings issued on May 5 created concern as temperatures fall to 24°F in parts of southwest, south central, southeast, and northwest Minnesota. Some areas avoid freezing temperatures, but many farmers are now checking fields for possible crop injury.
Liz Stahl, Extension Educator – Crops, Seth Naeve, Extension Soybean Agronomist, and Dave Nicolai, Extension Educator-Crops, shared guidance to help farmers evaluate frost impacts, crop emergence, and replant decisions during the early growing season.
Crop emergence depends on growing degree units, often called GDUs or growing degree-days. Corn usually requires about 90 to 120 cumulative GDUs for emergence, while soybean needs about 130 cumulative GDUs using a base temperature of 50°F. Farmers calculate GDUs by averaging the daily maximum and minimum temperatures and subtracting 50. In these calculations, temperatures above 86°F are recorded as 86, while temperatures below 50°F are recorded as 50.
Soybean plants generally need temperatures between 28°F and 30°F for several hours before serious frost injury occurs. Even when air temperatures reach 28°F, some emerged soybean plants may survive. Farmers are encouraged to wait 3 to 5 days before evaluating crop damage because recovery signs may take time to appear.
Corn plants have an advantage early in the season because the growing point remains below the soil surface until the V5 to V6 growth stage. Unless freezing temperatures reach deep enough into the soil to damage the growing point, many young corn plants are expected to survive frost conditions.
Farmers are also reminded to consider weed control, stand reductions, fuel costs, and long-term crop performance before making replant decisions.
In addition, the 2026 Strategic Farming Field Notes program will run every Wednesday morning from 8:00 to 8:30 from May 13 through August 12 using Zoom and podcast recordings. Register now for the series (you only need to register one time for the whole series) at z.umn.edu/strategicfarming. The educational series is supported by the MN Soybean Research and Promotion Council and the MN Corn Research and Promotion Council.
Photo Credit: getty-images-elhenyo
Categories: Minnesota, Crops, Corn, Soybeans