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Frost Damage In Small Grains And Corn

By Joel Ransom
Extension Agronomist for Cereal Crops
Air temperatures recently dipped below freezing in much of Northern midwest. Since most of the small grains had been planted and emerged and some of the corn, there is concern about the type of damage this cold weather may have caused. Temperature below freezing certainly have the potential to damage emerging crops. Nevertheless, the amount of damage is influenced by crop tolerance, growth stage, moisture content of the soil, duration of the sub-freezing temperature, location in the field, and environmental conditions before the occurrence of the sub-freezing temperature
Factors affecting frost damage
Crop – Cereal crops are generally considered to be frost tolerant early in their growth cycle. There is considerable variation for tolerance between crops, however. In general terms for the cereals grown in ND (and provided they are at the same stage of development), tolerance to freezing temperatures can be ranked in the following order: winter rye (most tolerant to frost) > winter wheat > oats > barley > wheat > corn (least tolerant).
Growth stage – One reason that cereals tolerate frost early in the season relative to broadleaf crops, is that their growing points remain below the surface of the soil for several weeks after emergence and are therefore protected from the extremes in the temperature of the air above. In small grains the growing point extends above the soil’s surface at about the six leaf stage or just prior to jointing and in corn at about the five leaf stage. Fortunately, all of the spring sown cereals in the state were still relatively young and their growing points were below the soil’s surface during the recent cold weather. Some winter wheat, however, has jointed and is potentially more susceptible to frost damage than its spring sown counterpart.
I would recommend that you carefully inspect growing points in your winter wheat if you had temperatures below 25 degrees for any extended period of time as the growing point is more susceptible to damage than leaf tissue during jointing. A damaged growing point will appear brownish or water soaked. A dead leaf may appear in the whorl if the growing point has been damaged. Prolonged (or very low) sub-freezing temperatures can kill growing points of cereal crops even if they are below the surface of the soil. Corn is the most sensitive and temperatures of less than 28 degrees can be lethal.
Environmental factors – Temperatures change more slowly in wetter soils than in dryer soils. Therefore, there is more risk of low temperatures killing plants if your soils are also dry. Plants are capable of hardening themselves against freezing and plants that had previously been exposed to near freezing temperatures are more likely to tolerate lower sub-freezing temperatures than those that have not. Most of the cereal crops were probably at least partially hardened before the arrival of the coldest weather last week. This may provide an additional level of protection. Cold air is heavier than warm air, so cold air will flow towards the lowest parts of your field, making frost damage more severe in these areas. When assessing frost damage, I would suggest that you visit the lowest spots of your farm first.
Inspecting for damage – Foliage that has been damaged by frost will initially appear yellow and within a few days turn black usually towards the tips of the leaf first. If the growing point was not damaged, after 3 to 5 days of reasonably warm weather, new growth should appear from the whorl. If this occurs, then you can be assured that the growing point was not killed. Loss of leaf tissue at this early stage will have little if any effect on yield.

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