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Impact of Freeze on Corn

Take note of the impacts these conditions might have on a germinating and emerging corn crop.

Early-planted corn emerged in some parts of Midwest before the recent frost and freeze advisory hit the region. On Monday, the USDA Crop Progress Report noted that 34% of the corn crop was in the ground, equal to the five-year average.

It’s important to take note of the impacts these conditions might have on a germinating and emerging corn crop, say Justin McMechan, University of Nebraska (U of N) crop protection and cropping systems specialist and Roger Elmore, U of N Extension cropping systems agronomist in a Crop Watch article.

“Now that the weather is improving, it’s good to start thinking about what the consequences might be and what to look for,” says Mark Licht, Iowa State University Extension cropping systems specialist, in an Integrated Crop Managment post.

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
  • Environmental conditions that follow the event

Yield Impacts from Freeze Damage

Early-season freeze damage results in a range of potential yield impacts, say McMechan and Elmore. 

Where is freeze damage likely? Severe damage is often limited to low-lying areas within a field because cool air is heavier than warm air, say the Extension researchers. 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, say McMechan and Elmore. However, if your area received a hard frost that penetrated the ground, it may have killed those plants as well. Regrowth of corn following freeze damage is often impeded by dead leaf tissue that can entrap new leaves. Plants significantly impacted by frost may experience delayed silking by seven to 10 days, say the Extension specialists. If conditions following the frost are wet and cool, plants may die from bacterial soft rot infections reducing plant stands.

Slow Emergence

“Heat unit accumulation has been negligible since April 26,” says Licht. “Rainfall had been near the climatological average prior to the recent rains. The effect of this weather pattern has resulted in April-planted corn taking more days to emerge. And that will be no different from corn planted the last week of April. All that matters is the day of emergence, not of planting.”

The impact of low temperatures and 2 inches of rain last weekend on yield potential is minimal according to a simulation model (FACTS) that accounts for biophysical factors on seedling emergence and crop growth, he says.

“While much of April had 4-inch soil temperatures above 50°F., for a good portion of the state there is concern about how much fluctuation there was at the 2-inch seed placement depth and what effect the fluctuation may have had,” says Licht.

If you don’t have freeze damage, there’s still an impact from cooler soil temperatures on your corn crop. Cooler temperatures lead to vigor loss (lower crop growth rates) which effect stand establishment, make the seedling more susceptible to herbicide (ALS) and insecticide (organophosphates) injury, more vulnerable to disease pathogen infection, and reduction in yield potential.

“The best way to assess the full impact of the weather on April-planted corn is to get into the field and conduct a thorough stand establishment assessment,” says Licht. “Determining the plant population is the first step. While determining the plant population, make note of emergence delays and any skips where plants should be.”

Plant skips should be evaluated to determine:

  1. If there was no seed due to planter error.
  2. If the seed did not germinate.
  3. If the seedling died before emergence.

Management Options

There are few management options after a major freeze event. Depending on the level of damage, options are to leave the crop, replant, or clip the dead plant tissue to prevent plants from becoming wrapped or tied, say McMechan and Elmore. 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 with nonclipped plants,” say the researchers.

Other studies found that post-frost clipping of corn plants reduced yields by 15% to 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, noted the U of N researchers.

Research conducted in south-central Nebraska by Elmore and Ben Doupnik evaluated three frost-damaged fields at V3 to V4 growth stage with varying levels of defoliation (100%, 70%, and 55%) for replant, clipping, and no treatment.

Results showed replanted corn yielded 22% to 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, but it did reduce yield and plant stands at the 100% defoliated site and reduced plant stands at the 70% defoliated field.

The variability could be due to numerous factors ranging from the temperature during clipping, cool conditions following frost leading to continued plant mortality as a result of Pseudomonas flourescens, or other pathogens such as bacterial stalk rot diseases also causing continued losses in early-season frost-damaged cornfields.

Considering Replanting?

The success of replanting corn depends on both the calendar date and prevailing environmental conditions, say McMechan and Elmore.  

Research in central Illinois found yield losses of 18% with replanting dates between May 9 and May 29. Planting in mid-June caused yields to decline rapidly with losses as high as 50%.

Research in Wisconsin found similar yield reductions for replanting after May 9:

  • 0.5% to 1.1% per day (0 to 2 weeks later)
  • 1.3% to 1.9% (2 to 4 weeks later)
  • 2.0% to 2.8% per day (4 to 6 weeks later)

Data from southern Iowa showed planting dates from April 17 to May 8 likely will result in 98% yield potential. Data from northwest and central Iowa indicates planting dates from April 15 to May 9 will likely result in 98% yield potential, according to McMechan and Elmore.

“Yield losses with later planting dates indicate the importance of properly evaluating the yield potential of the existing crop before replanting,” say the researchers. “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.”

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