Crop & Pest Report


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Cold Weather Impacts on Emerged and Emerging Crops (05/14/20)

The recent cold temperatures that have blanketed the state are nearly unprecedented for this time of the year. Monday morning, temperatures as low as 15 degrees were recorded at some NDAWN stations.

The recent cold temperatures that have blanketed the state are nearly unprecedented for this time of the year. Monday morning, temperatures as low as 15 degrees were recorded at some NDAWN stations. Moreover, most regions of the state and northeastern Minnesota experienced temperatures of 25 degrees or less. Since the rate of evaporation of soil water is largely determined by temperature, these low temperatures have dramatically slowed the rate of soil drying in regions that are still too wet to plant. This coupled with the recent rain and snow will no doubt further delay planting progress this year.

I have been asked if these sub-freezing temperatures damaged crops that have already been planted, including winter rye and winter wheat that are beginning to tiller. Small grains crops tolerate temperature as low as 25 degree. The extent of damage caused by sub-freezing temperatures depends on their growth stage, the temperature and the duration of the cold. Until the jointing stage, the growing point of small grains is partially protected from freeze damage as it is below the surface of the soil. Freeze damage most commonly results in the upper portions of exposed leaves becoming necrotic within 24 to 48 hours after the freeze event. Generally, these plants will grow out of the damage without any yield reduction. However, if air temperatures are cold enough for a prolonged period (a few or more hours depending on the soil type and moisture status), the soil temperature around the growing point can drop to the point that it will be lethal to the plant. There is greater risk of this type of freeze damage to small grains when they are grown in sandy soils and/or dry soils as these types of soils hold less heat than heavier and/or moist soils. Moreover, it is not uncommon to see more foliar freeze damage in no-till fields than in tilled fields as residues slows the movement of heat stored in the soil to the soil surface to help moderate temperature.

To determine if the growing point has been damage, dig up a few plants and remove the damaged leaves to expose the growing point. If the growing point is white in color it most likely is still alive. Growing points that appear yellow or brown are most likely dead. Winter wheat, winter triticale and winter rye are able to tolerate extremely cold temperatures after they are hardened in the fall. Nevertheless, winter cereals that have broken dormancy in the spring (started to regrow when temperatures in the spring are favorable), can be as susceptible to cold weather injury as spring cereals. See injury to winter triticale in Figure 1. Our winter wheat at Casselton did not show any freeze injury symptoms, and there were only a few damaged leaves on recently emerged spring wheat just north of NDSU. We expect these plants to develop normally once warmer weather returns.


I am not aware of any emerged corn in the state; there have been too few growing degree days this past month to permit emergence. Like small grains, however, the growing point of corn is below the surface of the soil until about the V6 stage, so corn can tolerate some freeze damage without adversely affecting yield potential. Corn, however, is more sensitive to cold temperatures than small grains as the lethal temperature for corn is 28 degrees. Though there are few planted acres in the state, the main concern with corn is the potential for mortality of the germinating seed when soils temperatures drop below 28 degrees. Keep an eye out for reduced emergence in low lying areas of fields where the bare soil temperature at a nearby NDAWN station dropped below 28 degrees.

Joel Ransom

Extension Agronomist, Cereal Crops

This site is supported in part by the Crop Protection and Pest Management Program [grant no. 2017-70006-27144/accession 1013592] from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed are those of the website author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

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