Kentucky Corn, Soybeans: Assessing Freeze Damage on Seedling Crops

    This seedling has damaged tissue that was at or near the soil surface. The rest of the plant is in good health and the plant should survive. Photo: University of Kentucky

    Corn and soybean plants were emerged in many fields when freeze events occurred last week across Kentucky and the surrounding region.  Farmers want to walk fields now and likely walked fields over the weekend. That is a normal reaction to freeze events.

    We need about 5 days of warm weather before freeze damage symptoms are clearly evident on plants and we can either see new growth or none. You may see hints of damage earlier than 5 days, but you won’t be able to identify the extent of damage in most fields.

    Soybeans

    We need about 5 days of warm weather before the freeze damage is evident on the crop. Any freeze damage below the cotyledons will kill the plant. If the cotyledons survive, then the soybean plant has full to nearly full yield potential. 

    Soybeans in the crook stage, where the plant is just emerging and the stem looks like a shepherd’s crook, are extremely sensitive to freezing weather. We can almost assume that soybeans at this stage are killed from the freeze.

    If most of the field was at this stage, then the farmer should plan to replant. Scouting the field about 5 days after the freeze is warranted, but one should expect to need to replant in these fields.

    For soybeans that had not emerged or soybeans with at least unifoliate leaves, the soybeans have a better chance of surviving. Sometimes, the upper leaves will insulate and protect the lower leaves. If the node at the cotyledon survives, the plant should survive.

    Corn 

    We need about 5 days of warm weather before the freeze damage is evident on the crop. I expect minimal yield loss on corn. I do expect nearly all aboveground growth to be frozen and dead, but I expect corn plants to survive.

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    For corn planted at the proper depth, the growing point is at least a half-inch below the surface. If that growing point survives, corn has 100% yield potential, even if all aboveground growth dies.

    The soil often buffers the freezing temperatures and insulates the growing point. Look for areas in the fields where:

    1. seeds are shallow – shallow seeds put the growing point closer to the soil surface
    2. furrows are not fully closed – open furrows allowing freezing to get to the seed quickly.
    3. areas of the field that are saturated: the higher water content will often freeze deeper in the soil than fields as field capacity
    4. expect there to be more damage in tilled fields, including “vertical tilled” fields. The reside from no-till provides a temperature buffer. I expect fields with cover crop residue to be buffered as well.

    Other Thoughts on Scouting and Assessing Damage

    When scouting either crop about 5 days after the freeze event, look for plants or plant structures that have turned brown or black. Look for signs of loss of turgor pressure. I think most aboveground damage will be easy to see in a few days.

    For corn, take a shovel and dig up a few plants to evaluate the growth above the seed. If there are no signs of brown/black areas on the plants, and if turgor pressure is good, then the seedlings are very likely to survive.




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