Wet conditions, below-average temperatures, soil conditions, disease, insects, and herbicide injury can put stress on corn germination and emerging seedlings causing concern about reduced corn stands. Before deciding to replant, determine the plant population in the field, the uniformity of the stand, and the uniformity of plant size. Consider a possible replanting date, the cost to replant, and any insurance or government program restrictions. Replanting is time-consuming and costly to producers, but it can be a viable agronomic practice given the right conditions.

Evaluate the Existing Stand

Although time is important when considering a corn replant, it is prudent to wait a few days before evaluating plant health or loss after a weather event. Plants may recover after submerged for a short time, lightly frosted, or partially fed on. Ultimately, a healthy growing point that escaped damage can resume growth and should be considered a survived plant. For decision-making purposes, it is critical to have a count of healthy surviving plants.

  1. While walking the field, measure 1/1000th of an acre based on row width (Table 1).
  2. Count the number of live plants along this measured distance of row.
  3. Repeat multiple times across the field or area in question.
  4. Average the counts and multiply by 1,000 to reach plant population per acre.
Table 1. Row length representing 1/1000th of an acre at different row widths.
Row length representing 1/1000th of an acre at different row widths

Compare Replant Potential to Current Stand

Yield potential changes as corn planting dates become later; therefore, it is important to evaluate the return on replant investment. Time and effort may be warranted where conditions have improved. Compare the yield potential of the reduced corn stand with the yield potential of a replanted corn stand (Table 2).

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

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: corners, ends, and washes. It is best done when these areas have nearly complete loss (less than 25% of the original stand surviving).2 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 is generally not recommended as this creates an environment of competition where the larger original plants compete with newly emerging corn plants.

When to Keep the Stand. A key consideration on whether to keep a reduced corn stand is to evaluate the yield potential of the existing stand. A reduced corn stand does not have the same yield potential as the target plant population, but yield potential may be higher than a replant. Trials conducted by the Ontario Corn Committee from 2006 through 2010 indicated that even with only one third of the target plant population remaining, yields decreased only 3 to 22%, depending on the location across Ontario.

Table 3. Expected grain yield due to various plant populations.3

Table 3 Average yields are indexed where the 30,000 plants/acre plant population equals 100. All data are derived from corn that was planted on or before May 10. Trials were conducted by the Ontario Corn Committee, 2006–2010.

Expected grain yield due to various plant populations

Table adapted from 2017 Agronomy guide for field crops Publication 811. Ontario Ministry of Agriculture, Food and Rural Affairs. http://www.omafra.gov.on.ca/.

What research does tell us is that a corn crop planted after May 25th, even with a perfect stand, may only have a maximum yield potential of 70%.1 The last date that should be considered to plant corn for grain in Eastern Canada is June 1st for areas below 80 RM (2300 CHU).

When to Terminate and Replant

There are many economic factors to consider in addition to the yield potential of a replant. The availability of early-maturing corn products with good yield potential and the cost of replanting are important factors in the replant decision.

Potential costs associated with replanting include:
  • Additional herbicides
  • Additional fertilizer costs
  • Additional spraying costs
  • Additional seed costs
  • Cost of an additional planting operation
  • Increased drying cost at harvest

A spreadsheet has been developed by the Ontario Department of Agriculture called the Ontario Corn Replant Decision Aid, found at this website: http://www.gocorn.net/v2006/Tool%20Descriptions.html. This spreadsheet takes into consideration the additional costs associated with a replant scenario along with the yield potential of the original corn crop and the yield potential of the late planted replanted crop

Replanted Corn Product Selection

Disease Tolerance. Consider planting corn products that have a higher tolerance to gray leaf spot and northern corn leaf blight as later planted corn fields can be exposed to these foliar diseases at earlier growth stages. Larger areas of leaf necrosis are associated with earlier infections during favorable conditions.

Insect Protection. It is important to consider insect trait package as later planted corn may have increased insect pressure. Late-planted corn may be at greater risk for second generation European corn borer damage. Such damage results in stalk breakage, dropped ears, and kernel feeding. Insect damage also creates pathways for diseases to infect.4 Corn rootworm can be more damaging to later planted corn because the larvae can feed on younger root systems beginning to form nodal roots instead of the well-established roots of earlier planted corn.5 Western bean cutworm (WBC) is a third pest that 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

Earlier Relative Maturity. Consider planting full-season corn products with adequate pest protection. Growing degree day requirements decrease as planting occurs after May 1st. Late corn planting research disagrees on actual yield loss differences between corn product maturities.7 End-of-season scenarios are unpredictable. However, corn products expected to reach physiological maturity prior to a killing frost can still be planted. Have flexible plans for drying grain moisture and storage at harvest.

Seeding Rate. Seeding rates do not necessarily need to increase with later planting dates. Warm soil temperatures associated with later planting dates should help germination. Seeding rates in mid to late May can be close to the target for final plant population.2 If an earlier corn product is being considered for the replant do not assume that a higher plant population will be required. Consult your local agronomist or seed expert, when considering a corn product change and adjust the seeding rate for the corn product selected for the replant.

Previous Stand Removal Options

Tillage. Tillage is the best option for removing corn stands with multiple herbicide tolerant traits and has no plant-back restrictions. A two-tillage pass may be needed depending on the growth stage of the original stand. May not be a good option where conservation tillage is desired for lack of moisture at planting.

Herbicides. Depending on the herbicide tolerance traits, corn can be terminated with clethodim and quizalofop (except corn products with quizalofop tolerance) products, which are labeled for the removal of corn. This method requires a plant back restriction. 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. Corn will need two to four leaves of growing green tissue for herbicides to be effective and 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.

Replanting to a Different Crop

After evaluating the yield potential of the current stand and considering potential replant scenarios, but either option is not acceptable, switching to another crop may be an option. In some situations, replanting with soybeans is the best economic option. It is important to consider applied herbicides and nitrogen programs as well as impact on crop rotation and plans for future years when making the decision to plant another crop.