Corn Replanting Decisions

Overview

Wet conditions and below-average temperatures can put stress on corn germination and emerging seedlings, causing concern about reduced corn stands. Before deciding to replant, evaluate the stand for population and uniformity, compare the yield potential of the existing stand with the yield potential of the replant, and consider insurance or government program restrictions. Replanting is time consuming and costly to growers, but it can be a viable agronomic practice given the right conditions.

Count and Evaluate Existing Stand

Although time is of the essence when replanting corn, it is prudent to wait a few days before evaluating plant health or loss post-weather event. Plants may recover if submerged for a short time, lightly frosted, or only partially fed on. Ultimately, a plant should be counted as having survived if it has a healthy growing point that can resume growth. Having a count of surviving plants is helpful for making replanting decisions.

One way to evaluate corn stands is to count the number of live plants in a length of row equal to 1/1000^th of an acre based on row width (Table 1) and then multiply that number by 1,000 to determine the number of plants per acre (ppa). Repeat the process in several locations in the field.

Table 1. Row length representing 1/1000^th of an acre at different row widths.¹

An alternate method is to count 150 plants in a row and then measure the distance from start to finish. Divide the number of feet traveled into the appropriate factor in Table 2 to calculate plant population. For example, if you walked 94 feet while counting 150 plants in 30-inch rows, the population is 2,613,600 ÷ 94 = 27,804 plants per acre. This may provide a more accurate estimate since a longer row length is counted, which uses a larger representative area and thus requires fewer locations to be sampled. Use the same factors for both 30-inch twin- and single-row stand counts; however, the plants in both the twin rows should be counted.

Table 2. Stand count evaluation factors, by row width, for measuring the distance when counting 150 plants.¹

To read more on taking early corn stand assessments see Assessing Corn and Soybean Stands

Compare Replant Potential to Current Stand Assessment

Yield potential changes as corn planting dates shift later in the season, so it is important to evaluate the return on replant investment. The time and effort needed for the replant may be warranted where conditions have improved. Evaluate reduced corn stands and compare to the percent of optimum yield a replanted stand could yield (Table 3).

Table 3. Potential corn yield at harvest based on planting dates and plants per acre.²

Spot, Keep, or Terminate Corn Stands

When to Spot Plant

Successful spot planting could be applied to large areas of fields with early season loss, like corners, ends, and washes. It is best done when these areas have less than 25% of the original stand surviving.¹ While these areas may be successfully replanted, special consideration should be given to area-specific agronomic management, inputs needed, and weather influences on the ultimate outcome. The same corn products should be used when replanting a portion of a field. Inter-planting into a poor stand generally creates an environment of competition where the original plants are larger and compete with newly emerging corn plants.

When to Keep the Stand

As populations drop below 20,000 plants per acre, grain production is not compensated from reduced competition within the row.¹ An economic analysis of seed cost, market price, and expected yield is individual for each field. As irrigated corn populations drop to 24,000 plants per acre, yield can become noticeably reduced by 6 to 9%. This similar yield loss is expected for dryland corn with stands reduced to 18,000 to 20,000 uniform plants per acre.²

When to Terminate and Replant

Demonstrations at The Bayer Crop Science Learning Center at Scott, Mississippi simulated a field with 100% stand loss 25 days after planting (and replanted to 36,000 seeds per acre). The replanted field had a 16.25 bushel per acre yield reduction compared to the check field left as originally planted. In another simulation, a 30% stand loss 25 days after planting (and replanted to 36,000 seeds per acre) had only a 6 bushel per acre yield reduction compared to the check left as planted.³ These scenarios demonstrate yields can be improved to near expectations when stands are completely removed before replanting.

Corn Product Seed Decisions

Corn Products with Disease Tolerance

Later planted corn fields can be exposed to foliar diseases such as gray leaf spot and northern corn leaf blight at earlier growth stages. Larger areas of leaf necrosis are associated with earlier infections during conditions favorable for disease development.

Corn Products with Insect Protection

Late-planted corn may be at greater risk for second generation European corn borer damage. Such damage results in stalk breakage, ears dropping off, and kernel feeding. Insect damage also creates pathways for diseases to infect the plants.⁴ Corn rootworm can cause greater stress to late-planted corn because the larvae feed on younger roots beginning to form nodal root systems instead of the well-established roots of earlier planted corn.⁵ Western bean cutworm (WBC) also targets late-planted corn. Typically, the moth flight of WBC peaks in mid-July, a time when late-planted corn could be in late whorl stage while earlier planted fields have tassels. Late whorl is the corn stage preferred by WBC for egg laying.⁶ Traits offer season-long insect protection and should be considered in late-planted corn.

Corn Products with Earlier Relative Maturity

When replanting, consider full-season corn products with adequate pest protection. Growing degree day requirements decrease when planting occurs after May 1. Late corn planting research has disagreed on actual yield loss differences between corn product maturities.⁷ End-of-season scenarios are unpredictable. However, corn products expected to mature safely in the fields can still be planted. Have flexible plans for drying grain moisture and storage at harvest.

Seeding Rate

Optimal seeding rates do not necessarily need to increase with later planting dates. Warm soil temperatures give seeds a vigorous advantage with late planting dates. Seeding rates in mid to late May can be close to the target for final plant population.¹

Old Stand Removal Options

Tillage

Tillage is the best option for corn stands with multiple herbicide tolerant traits that have no plant-back restrictions. A two-tillage pass may be needed depending on the growth stage of the original stand. Due to the loss of soil moisture, however, this may not be a good option in areas that are typically drier, in which case removal with herbicides may be the better option.

Herbicides

Corn with stacked herbicide tolerance traits can be terminated with a product containing clethodim, such as Select Max^® Herbicide with Inside Technology™, labeled for removal of corn. This option comes with a waiting interval to plant. To avoid plant back restrictions for small corn (V1 to V3), growers can apply a combination of paraquat and metribuzin.⁸

Corn with only one herbicide tolerance trait can be terminated with herbicides it is susceptible to. Herbicides may be effective at terminating corn with two to four leaves of growing green tissue, though complete kill could take longer than three weeks. Consult your chemical or Bayer representative for local tank mix recommendations to remove corn stands stacked with herbicide tolerant traits.

Table 4. Tank mix options for removing corn for replant.

Sources

¹Nielsen, R.L. 2017. Corn replant considerations 2017. Purdue University. http://www.kingcorn.org/news/articles_17/CornyDecisions-0508.html

²Larson, E. and Bond, J. 2013. Corn replanting guidelines and management issues with wet weather. Mississippi State University. https://www.mississippi-crops.com/2013/04/26/corn-replanting-guidelines-and-management-issues-with-wet-weather/

³Evaluation of Genuity^® VT Triple Pro^® Corn at different planting dates. 2010. Monsanto Learning Center Summary. Scott, Mississippi.

⁴European corn borer (Ostrinia nubilalis Huber). Purdue University. European Corn Borer E-series 17-W. https://ag.purdue.edu/department/entm/extension/field-crops-ipm/_docs/european-corn-borer_corn.pdf

⁵Nielsen, R.L. 2002. Timing of crop stress is critical! Purdue University, Corny News Network. https://www.agry.purdue.edu/ext/corn/news/articles.02/LatePlanting_CRW-0705.html

⁶Peterson, J., Wright, R., Hunt, T., Ohnesorg, W., and Bradshaw, J. 2016. Begin scouting for western bean cutworm eggs in corn. University of Nebraska–Lincoln, Cropwatch. https://cropwatch.unl.edu/2016/begin-scouting-western-bean-cutworm-eggs-corn/

⁷Nielsen, R.L. 2022. Hybrid maturity decisions for delayed planting. Purdue University, Corny News Network. https://www.agry.purdue.edu/ext/corn/news/timeless/hybridmaturitydelayedplant.html

⁸Zimmer, M. and Johnson, B. 2020. Control of “volunteer” corn in a corn replant situation. Purdue Extension, Pest and Crop Newsletter. https://extension.entm.purdue.edu/newsletters/pestandcrop/article/control-of-volunteer-corn-in-a-corn-replant-situation/

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