With dry conditions the last week and a forecast for rain this weekend, corn planting is progressing rapidly in Nebraska. While warm conditions may persist through April, the potential for freeze risk can still be high when early-planted corn emerges.
A recent CropWatch article by Tyler Williams and Al Dutcher noted “Certainly elevation plays a key role in freeze risk during May, so we should not be surprised by how often freezing temperatures occur in May at higher elevations. Also… freezes have occurred in May in three of the last five years across eastern Nebraska.”
Freeze damage occurring after the 6th leaf stage, when the growing point emerges above the soil line, can reduce corn stands and yields.
Impact of Freeze on Corn Seeds and Seedlings
The extent of freeze or frost damage to corn depends on
- the low temperature,
- duration of exposure at that low temperature,
- corn development stage,
- water status of the plant, and
- the environmental conditions that follow the event.
Dry corn seeds can withstand 14°F to 23°F for two days; however, seeds that are exposed to moist conditions at 68°F and germinate one to two days prior to experiencing these same cold temperatures will be killed. One research study found that kernel uptake of water or imbibition at temperatures near 41°F can result in malformed seedlings and reduced seedling growth rate for low-moisture kernels (6%) whereas high moisture kernels (13%) appeared to be unaffected at similar temperatures.
Genetic variation exists in corn for this trait. Once emerged, young seedlings are easily damaged by freezing temperatures, but remain viable as long as the growing point is unaffected.
Early-season freeze damage results in a range of potential yield impacts. Severe damage is often limited to low-lying areas within a field because cool air is heavier than warm air. As a result, frost damage to plants can range from slight to severe in a single field. Early season survival of corn plants is attributed to growing-point protection below the soil surface; however, a hard frost can penetrate the ground and kill plants.
Regrowth of corn following freeze damage is often impeded by dead leaf tissue that can entrap new leaves; this leads to abnormal growth commonly known as “buggy whipping”. Plants significantly impacted by frost may experience delayed silking by 7 to 10 days.
Farmers have few management options after a major freeze event. Depending on the level of damage, they may decide to leave the crop, replant, or clip the dead plant tissue to prevent plants from becoming wrapped or tied. Replanting corn affected by frost will depend on numerous factors such as potential planting date, frequency of plant death, replanting cost, and seed availability.
Clipping frost-damaged plants has led to highly variable results. In one study clipping heights greater than 1 inch was found to increase grain yields by 40% compared to non-clipped plants. In contrast, Carter (1995) found that post-frost clipping of corn plants reduced yields by 15-34% at three sites with two of these sites showing no differences with unclipped plants and one showing a 10% increase in yield for clipped plants.
Research conducted in south central Nebraska by Roger Elmore and Ben Doupnik (1995) evaluated three frost-damaged fields at V3-V4 growth stage with varying levels of defoliation (100%, 70%, and 55%) for replant, clipping, and no treatment.
Replanted corn yielded 22%-90% greater than corn with 100% defoliation, no differences were observed with 70% defoliation, and a yield loss was observed when comparing replanting and a field with 55% defoliation. Clipping plants did not increase yields at any site, but did reduce yield and plant stands at the 100% defoliated site and reduced plant stands at the 70% defoliated field.
The variability of corn response to clipping could be due to numerous factors. Temperature during clipping can have a significant impact on corn plants. Johnson (1978) found that clipping corn plants under high temperatures (86-90°F) reduced stands by more than 90%. None of the previous studies noted temperature at time of cutting, but it is possible that this could influence the yield potential of cut plants.
Elmore and Doupnik indicated that cool conditions following frost could lead to continued plant mortality as a result of Pseudomonas flourescens. This bacterial soft rot disease does not typically cause a problem in corn fields; however, several days of cool and humid weather following the frost event in 1995 allowed the bacteria to cause continued stand loss. Other pathogens such as bacterial stalk rot diseases also could cause continued losses in early-season frost damaged corn fields.
In 2014 after widespread hail, corn in the early growth stages became infected with a bacterial stalk rot disease suspected to be Pectobacterium carotovorum. Clipping could provide a means of widespread dissemination of bacterial pathogens in the field leading to increased yield losses.
Herbicide Resistance Info
The success of replanting corn depends on both the calendar date and prevailing environmental conditions. Nafziger (1994) found yield losses of 18% with replanting dates between May 9 and May 29 in central Illinois. Planting in mid-June caused yields to decline rapidly with losses as high as 50%. In Wisconsin Lauer et al. (1999) found similar grain yield reductions for replanting after May 9: 0.5%-1.1% per day (0-2 weeks later), 1.3%-1.9% (2-4 weeks later), and 2.0%-2.8% per day (4-6 weeks later).
Data from southern Iowa – perhaps similar to southeast Nebraska conditions – indicates planting dates from April 17 to May 8 likely will result in 98% yield potential; data from northwest and central Iowa – perhaps similar to northeast Nebraska conditions – indicates planting dates from April 15 to May 9 will likely result in 98% yield potential.
Yield losses with later planting dates indicate the importance of properly evaluating the yield potential of the existing crop before replanting. These evaluations should only be made after the crop has had adequate time for regrowth following the frost/freeze event. Replant decisions should also consider weed competition, herbicide options, seed availability, field conditions, and the cost of equipment.