Data from Beck’s Practical Farm Research (PFR)® (https://www.beckshybrids.com/PFR/About-PFR) and many universities have shown that over time, early planting is a good strategy to achieve high yields. Early planting carries risks of delayed germination due to cold soil, compaction from high soil moisture, and frost damage just to name a few. Here, we talk through frost damage: where to look, symptoms, and how to assess the long-term impact.
Early-season frost damage is a stressful physiological event that can slow plant development. The net impact of early-season frost on a corn or soybean plant will depend on the health of the plant before the frost, the extent and duration of the freezing temperature, and the growing environment following the frost event.
In general, corn seedlings are at a lower risk of death from freezing temperatures than are soybeans because the growing point of corn remains below ground later in the spring until the V5 to V6 growth stage.
Here are common areas where frost occurs:
- Low lying areas: Even a 1- to 2-in. depression is more vulnerable to frost.
- High residue areas: Residue slows the springtime soil warming processes.
- Dry, loose soils: They tend to lose heat more rapidly than moist or compacted soils.
Freeze damage on most plant tissue creates water within the leaf freezes and ruptures cells.
Frost Damage to Corn
Frost damage on emerged corn plants has been observed from April until mid-June. Corn plants will not be killed by frost unless temperatures drop low enough to drive the cold into the soil and kill the growing point that is positioned 0.75 in. below the soil surface. Corn that has not emerged is typically well insulated from frost damage.
Corn is most vulnerable when it’s recently emerged or early vegetative growth with tender leaves, and anytime air temperatures dip below 32°F for extended periods.
Frost damage to corn can show up one to two days after the freeze event. It results in water-soaked leaves, and limp and brown leaves. Three to four days later, new green leaves will emerge from the whorl.
If, after three or four days, new leaves are not visible or emerging, check the growing point for discoloration. Carefully dig the young plant from the soil and split the plant lengthwise to observe the growing point. Healthy tissue will be white, cream or light-yellow color – any other color indicates that the growing point is damaged. A common complication of a strong frost or light freeze on V2 to V3 growth stage corn is that the leaf-tips get “tied-up” and further restrict new leaf emergence. Under subsequent cloudy, cool and moist conditions, visual recovery can take 7 to 10 days.
Corn plants with damaged leaf tissue will often get “tied up” when they grow new, healthy tissue.
In this picture, the growing point is water soaked and dark- this plant will not recover from this damage. Photo: Luke Schulte
Frost Damage to Soybeans
Although subject to frost as well, soybeans often escape similar injury due to plant development and to typical planting dates past the average last frost date.
Upon emergence, the growing point of a soybean plant is above the soil surface and less insulated against frost. Soybean cotyledons are thick compared to leaves. Therefore, cotyledon stage soybeans are more tolerant to freezing temperatures than older soybean or young corn leaves. When the frost only affects the top of the soybean plant, those plants with one or more intact cotyledons recover from surviving axillary buds.
Soybeans are most vulnerable if the air temperature stays at or below 28 to 30°F for several hours. Additionally, hooking stage soybeans will be killed if the hypocotyl tissue below the cotyledons is killed.
Symptoms of frost damage include water-soaked lesions on the cotyledons, leaves or hypocotyl.
Check for firm, healthy hypocotyls, cotyledons, and growing points. In soybeans, the growing points are above ground at emergence and are exposed after the cotyledons open. Freezing of all growing points is fatal. However, soybeans can compensate better for partial stand losses than corn.
Soybean cotyledons damaged by frost.
The hypocotyl (stem below the cotyledons) is damaged, so this plant will not recover. Photo: Luke Schulte
Frost damage is often visible immediately. Assessment to occur damage should occur three to four days after the frost event when plants have had an opportunity to show new growth. During this field scouting, if a significant portion of the stand is not showing signs of recovery, you may need to consider replanting. Your local Beck’s Representative (https://www.beckshybrids.com/Quick-Links/Contact-Us) can provide more information about evaluating a stand for replanting, and the Beck’s 100% free replant policy.
An early frost can have an impact on grain yield, but the trade-off between planting date impact on yield is generally greater than the frost damage impact on yield. Delayed planting further impacts profitability due to management delays, and higher harvest moisture and increased drying costs with corn.
The benefits of early planting can often outweigh the risk of frost damage. If you have more questions about assessing frost damage or other early season risks to your corn and soybean crops, reach out to your trusted advisor.
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