Farmers Should Assess Corn and Soybeans for Frost and Freeze Damage

By Clair Keene and Ana Carcedo

Many areas of North Dakota experienced their first fall frost of the season the weekend of Sept. 5-7. While most North Dakota Agricultural Weather Network (NDAWN) stations stayed close to a minimum temperature of 32 degrees Fahrenheit, a few stations recorded lower temperatures with some upper 20s observed. The Dickinson NDAWN station fluctuated between 32 and 33 degrees Fahrenheit for five hours between 3 and 7 a.m. the morning of Sept. 6. The Hettinger station ranged between 32 and 30 degrees Fahrenheit for four hours early Saturday morning.

“Today marks five days out from the frost and freeze events of last weekend,” says Clair Keene, NDSU Extension small grains agronomist. “Based on the temperatures observed, farmers should assess their crops for damage now in order to make timely harvest and marketing decisions going forward.”

Corn assessment

Corn can be killed at 32 degrees Fahrenheit if the temperature stays at freezing for a few consecutive hours, usually thought to be three to four hours, says Keene.

Corn plant death occurs more quickly at colder temperatures, with exposure at 28 degrees or less for just 15 minutes being sufficient to kill most tissues. When temperatures are just above freezing, 33 to 40 degrees Fahrenheit, for multiple consecutive hours, damage is likely to be highly variable and strongly influenced by the topography of the field. Cold air is heavier than warm air, and as air cools, it flows to lower positions on the landscape. If a corn field has rolling hills or is adjacent to a low creek bed, farmers should expect to find more damaged plants in the swales or along the drainage points.