The potential for cold injury to corn seedlings is influenced by growth stage, air temperature, soil moisture, and soil texture. Freezing temperatures above 28 °F may damage seedling leaf tissue without injuring the growing point. Temperatures below 28 °F may injure or kill the growing point even if it is below the soil surface. Farmers should wait 3 to 5 days after a freeze to accurately assess plant damage.
Freezing temperatures can damage corn seedlings, particularly if the temperature drops to or below 28 °F. Within the first 24 hours after freezing temperatures, the leaves may turn yellow, silver, or brown and may become wilted or water-soaked (Figure 1 and Figure 2, top). After several days, the leaves may die. The stem may also turn brown; however, if the growing point is not damaged, there is a good chance the seedling can recover, particularly if there is new green tissue in the whorl (Figure 2, bottom).1 A firm, white or cream-colored growing point is a good indication that the seedling is alive and the probability for recovery is very good. Seedlings with soft and dark-colored growing points are likely to die. Under favorable weather, a new leaf should develop and appear 3 to 4 days after the frost. Occasionally, decaying leaf tissue may inhibit the growth of new leaves from the whorl, giving the seedling a twisted appearance.
Typically, the growing point will be below the soil surface from the time the seedling spikes until the V5 growth stage. Growth stages in corn are identified by the number of leaf collars showing (Figure 3). A pictorial guide to the location of the growing point at different corn growth stages is available online at http://kingcorn.org.2 If the growing point is below the soil surface and the soil temperature remains above 28 °F, the seedling can usually recover rapidly from a moderate frost. Temperatures at or below 28 °F for a few hours can be lethal and may kill the growing point even if it is below the soil surface. The loss of 4 to 5 leaves may have minimal impact on corn yield potential.3 The amount of green tissue a seedling has available to support regrowth helps increase the likelihood of recovery. Multiple frost events or cool, damp weather following a frost event can compromise recovery.
The best management practice is to exercise patience and scout the field 3 to 5 days after a cold temperature event to accurately assess plant survival. While scouting, look for evidence of new leaf growth from the whorl and split stems to evaluate the condition of the growing point. Cool days following a cold temperature event may delay recovery and the diagnosis of the extent of injury. Corn yield potential is primarily affected by stand loss, not the degree of leaf damage.1 After assessing the condition of several plants, stand counts should be taken to estimate the potential number of surviving plants. The estimated yield potential of the existing stand should be compared with the estimated yield potential of a replanted stand to help determine if replanting would be economical.
1Nielsen, R.L. 2001. Frost and low-temperature injury to corn and soybean. Corny News Network. Purdue University.
2Nielsen, R.L. 2008. Growing point location in corn at different growth stages. Purdue University. Corny News Network. Purdue University. http://www.kingcorn.org
3Elmore, R.W. 2015. Impact of early season frost (before V4). Iowa State University. http://www.agronext.iastate.edu.
Web sources verified 2/2/18