Can My Crops Take These Cold Temperatures?

By Sara Berg

SDSU Extension Agronomy Field Specialist

It has been unseasonably cold and snowy…now what? There are a few things to keep in mind as Mother Nature temporarily brought back the wrath of winter. Many farmers in Southeastern South Dakota began corn planting within the last two weeks. According to the USDA NASS, 7% of corn and 2% of soybean was planted across the state of South Dakota as of May 1. Small grain planting is wrapping up with 84% of spring wheat and 84% of oats planted. Depending upon planting date and growing degree-days, some corn may have reached germination, causing concern for cold damage. About half of South Dakota spring wheat and oat crops have emerged, raising similar questions. Alfalfa has emerged and in most areas, is well on its way to development.

How does frost damage work?

A killing or “lethal” frost can have a much different effect on your crop than a “simple” frost. If temperatures reached 32°F or lower in your area for a few hours, you have experienced a simple frost; however, if temperatures dipped to 28°F for a measurable period, you may have experienced a lethal frost.

In corn, the growing point remains underground until about the 5-6 leaf stage (V5-V6 stage), so there is some protection from frost due to air temperature. In a simple frost, plants may experience die-off of above ground plant parts. Corn can be quite resilient to this, and recover in early growth stages with minimal to no yield loss. However, a killing or lethal frost can produce much different results. If the air temperature was at or below 28°F for several hours, your germinated corn seedling may have experienced damage or death, even though its growing point is underground.

Small grains are much more resilient to such temperatures. Even with loss of above ground tissue due to a lethal frost, plants can survive, but may see injury. However, after jointing, the growing point is above ground and from boot to flowering temperatures below 28°F can be lethal. Overall, plant damage depends upon the planted variety/hybrid, soil temperature, air temperature, length of freeze, crop growth stage, field topography, and soil moisture.

How do I tell if I have injury to my crops?

Be patient. No one likes to hear “Let’s wait and see” but it is imperative to do so. At this point, your best management strategy is to wait approximately 1 week following concerning temperature events to check plants for injury. With current cold temperatures, corn and small grain development can be significantly slowed from what many perceive as the “norm” this time of year, so patience in checking seedling development is vital.

When scouting for injury, be sure to check different parts of fields, low-lying areas and field edges may be more prone to cooler temperatures than other areas. In corn or small grain, if no plant tissue is visible, split seedlings lengthwise, and check the growing point, if it is brown/grey and soft, the plant will likely not survive. Yellow or white/cream growing points indicate a healthy corn or small grain plant, respectively, with recovery potential. If there was tissue development, surviving plants will show new green tissue but there may be some root curling or malformation. Those that are highly effected or dead will show no improvement after the frost.

After cold injury, most yield loss is due to stand loss rather than leaf damage. If a stand is deemed significantly impacted after the weeklong wait period, replanting options should be carefully considered.

Other Considerations

Be sure to consider the effect of damp, cold weather on plant disease risks as well as regular growth and development. At this point, farmers are wrapping up small grains and the focus is moving to row crops. Remember that many soil borne pathogens can substantially affect both corn and soybean emergence due to cold, wet soils, with root and seedling rots being a major factor. These conditions may compound plant health issues if factors such as soil crusting, ponding, compaction, or potential herbicide injury exist as well.