This guide can be applied to corn grain production in the southern U.S. for high, moderate and low expected yield levels for key hybrids grown in the south.

1. FIELD FACTS • VOL. 13 • NO. 5 1
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DUPONT PIONEER AGRONOMY SCIENCES
Corn Grain Stand Evaluation / Replant Guide for Southern U.S. Planting
Each year insects, weather and seedbed conditions present
challenges to stand establishment in some corn fields in the
southern U.S. This leaves affected growers with the dilemma
of incurring additional costs to replant the field or attempting
to meet their economic yield goal with an imperfect stand.
The following information is designed to assist growers in
assessing a reduced-stand situation. This guide can be applied
to corn grain production in the southern U.S. for high,
moderate and low expected yield levels for key hybrids
grown in the south. Additionally, this guide provides a step-
by-step process for determining yield losses due to stand loss,
missing plants, uneven stands and planting delays.
Assessing Your Stand
Table 1 provides the measurements required to equal 1/1000th
of an acre. To obtain a reasonable estimate of plant stand for
a given field, measure off the appropriate distance for the row
width indicated below, count the number of plants expected
to survive damage and multiply by 1,000. The accuracy of
the stand count depends on the number of locations sampled
within the field. As a general rule, at least 8 locations should
be measured to represent a 40-acre field, or about one sample
per five acres. Record the average number of surviving plants
next to “Step 1: Surviving Stand” in Worksheet 1.
Table 1: Row lengths needed to equal 1/1000 of an acre.
Row Width Length of Row
40" 13'1"
38" 13'9"
36" 14'6"
30" 17'5"
Yield Estimation
Tables 2, 3 and 4 contain hybrid responses to seeding rate
data for several key southern hybrids broken out by yield
level. Select the table that best represents the yield level of
the field in question, and then use that chart to estimate your
field’s percent of optimum yield using the surviving plant
stand calculated in Step 1. Record this percent next to “Step
2: Expected Yield %” in Worksheet 1.
Assessing Gaps in Stand
Yield loss can also occur from uneven spacing of the
surviving population. The more common the gaps and the
longer the gaps, the greater the yield loss potential (Johnson
and Mulvaney, 1980).
• If stand loss is less than 25% of original population, enter
0% next to “Gap % Yield Loss” in Worksheet 1.
• If stand loss is greater than 25% and average gap length is
less than 3 feet, enter 2%.
• If gaps are 3 feet or greater, enter 5% (Nielsen, 2003).
Table 2: Percentage of optimum yield at various populations
(high yield environments; 180+ bu/acre expected yield).
Pioneer®
Brand
Hybrid
Family
Final Stand (plants per acre in thousands)
20 22 24 26 28 30 32 34 36
Percent of Optimum Yield
P0912 87 90 93 96 97 98 99 99 100
P1319 79 83 87 90 93 94 97 98 100
P1498 84 87 90 92 94 96 98 99 100
P1690 89 91 93 95 96 97 98 99 100
P1745 90 93 95 97 98 99 99 100 99
P2023 81 85 89 93 95 97 98 99 100
P2088 87 89 93 95 97 98 99 99 100
Average 85 88 91 94 96 97 98 99 100
Table 3: Percentage of optimum yield at various populations
(moderate yield environments; 140-180 bu/acre expected yield.
Pioneer®
Brand
Hybrid
Family
Final Stand (plants per acre in thousands)
20 22 24 26 28 30 32 34 36
Percent of Optimum Yield
P0912 94 95 97 98 99 99 100 99 99
P1319 90 92 95 97 98 99 100 100 99
P1498 88 91 95 96 97 98 99 100 99
P1636 88 90 94 95 96 98 99 99 100
P1690 94 96 97 98 99 100 99 99 98
P1745 88 92 95 97 99 99 100 99 98
P2023 88 92 95 97 99 99 100 99 98
P2088 93 95 96 98 99 99 100 99 99
Average 90 93 96 97 98 99 100 99 99
Source: 2006-2012 DuPont Pioneer population trials conducted
predominantly at research stations near Union City, TN, Cairo, GA,
Kinston, NC, and Princeton, IN.

2. 2
Assessing Delays in Development
Delays in corn seedling development can also have a negative
impact on yield (Carter et al., 1992).
• If surviving plants are uniform (within 2 leaf stages of
each other), enter 0% next to “Step 4: Delayed Plants %
Yield Loss” in Worksheet 1.
• If ¼ of the stand is delayed by 2 to 3 leaf stages, enter 6%.
• If ½ of the stand is delayed by 2 to 3 leaf stages, enter 8%.
Table 4: Percentage of optimum yield at various populations
(low yield environments; less than 140 bu/acre expected yield).
Pioneer®
Brand
Hybrid
Family
Final Stand (plants per acre in thousands)
20 22 24 26 28 30 32 34 36
Percent of Optimum Yield
P0912 92 95 98 99 100 99 97 96 94
P1319 96 98 99 100 100 99 99 98 97
P1498 89 92 95 97 98 100 100 98 97
P2088 94 95 97 99 100 100 100 98 96
Average 93 95 97 99 100 100 99 98 96
Source: 2006-2012 DuPont Pioneer population trials conducted
predominantly at research stations near Union City, TN, Cairo, GA,
Kinston, NC, and Princeton, IN.
Worksheet 1: Gross Returns Current Crop
Complete the following to estimate gross $ returns on current
crop.
Worksheet 1
Step 1: Surviving Stand (Table 1) ____________
Step 2: Expected Yield % (Table 2, 3, or 4) ____________
Step 3: Gap % Yield Loss ____________
Step 4: Delayed Plants % Yield Loss ____________
Step 5: Total Expected Yield (%)
Subtract Step 3 & 4 from Step 2 ____________
Step 6: Normal 5-Year Avg. Yield (bu/acre)____________
Step 7: Expected Yield (bu/acre)
Step 5 x Step 6 ____________
Step 8: Grain Market Price ____________
Step 9: Expected Gross Returns Current Crop
Step 7 x Step 8 ____________
Worksheet 2: Gross Returns Replanted Crop
Complete the following to estimate gross $ returns on
replanted crop assuming uniform stands and even emergence
of replanted corn in the next column.
Worksheet 2
Step 1: Normal 5-Year Avg. Yield (bu/acre)____________
Step 2: Expected Yield % (Table 5) ____________
Step 3: Expected Yield (bu/acre)
Step 1 x Step 2 ____________
Step 4: Grain Market Price ____________
Step 5: Expected Gross Returns Replanted Crop
Step 3 x Step 4 ____________
Step 6: Cost of Removing Existing Crop ____________
-Herbicide and Application
-Tillage (if used)
Step 7: Replant Costs ____________
-Seed Bed Preparation
-Replant Seed
-Herbicide
-Insecticide
-Fertilizer (N/Starter)
-Labor
-Other
Step 8: Expected Gross Returns Above Added Costs
Replanted Crop
Step 5 - Step 6 - Step 7 ____________
Table 5. Influence of planting date on optimum corn yield for
various regions of the U.S. assuming optimum plant
populations. a,b
Planting
Date
Region
Mid-West Mid-South
------- % of maximum yield ----------
March 20 --- 93
March 30 --- 95
April 1 99 97
April 10 100 97
April 20 100 98
April 30 97 96
May 9 93 93
May 19 86 86
May 29 78 82
June 8 67 68
a
Source: Emerson Nafziger, Eric Adee, and Lyle Paul, Univ. of
Illinois; Jason Kelley, Univ. of Arkansas, and Erick Larson,
Mississippi State University.
b
Mid-South data generated from plots grown under irrigation in MS
and AR using hybrids containing Bt genes. Percentages may not
accurately reflect yield levels for low yield potential dryland
environments. Data collected from 2008-2010 in AR and from
2009-2011 in MS.

3. 3
Making the Decision
Compare the expected returns of the current crop (worksheet
1) and the expected returns of the replanted crop (worksheet
2). Are the returns to replant higher? If yes, the decision
becomes easier to make. If Mother Nature cooperates and
historic yield trends hold true, you should be dollars ahead.
By replanting and establishing a consistent stand, you also
eliminate weed control challenges in thin stands.
Unfortunately, reduced stands are never consistent across the
field and large pockets of extremely thin stands normally
occur. This is where the “art” of farming overrides the
science. Will these field areas produce challenges for weed
control? How much additional yield loss will occur due to
extremely thin areas? Can only the pockets be replanted?
How will harvest of the field be affected?
Even if the calculation demonstrates that costs are greater
than or equal to the potential gain, some growers may still
decide to replant. For those growers the irritation of starting
out with a poor stand and limited crop potential simply
outweighs the economic advantage of keeping the stand.
Although appropriate for “close calls”, emotion in this
decision can be costly and should generally be avoided.
Other Considerations
Below is a list of other items to keep in mind when making a
replant decision:
• A thin stand is better than no stand at all. Remember to
finish planting the remainder of your fields (for crop
production with the same planting window) before
replanting a field.
• It’s important to remove the existing thin stand before
replanting. Patching in additional seeds next to a thin
stand is rarely beneficial and creates challenges due to
differences in spacing and timing of crop growth and
development (e.g., competition between plants,
pollination timing and harvest maturity timing). Removing
the remaining stand can be accomplished by:
o Mechanical tillage
o Herbicide applications. Where the original stand is
Roundup Ready®
, the most efficacious option is
likely to be Select Max®
at 6 oz/acre, 6 days prior to
replanting, especially if translocation is needed on
very small corn and corn that is barely emerged. Be
sure to check the label before applying. Other
treatment options that have proven efficacious and
that allow immediate plant back include paraquat
mixed with linuron, diuron, or metribuzin. Metribuzin
is only labeled for corn plant back in some states.
Check labels for more specific information. Also
check with your local chemical supplier or Extension
Service professional for specifics on product rates
and restrictions.
• If replanting will occur a little on the late side of the
“normal window”, consider the challenges this will
create. Additional management may be required to
prevent or minimize yield-limiting factors such as:
o Heat stress during pollination (timely irrigation
needed where possible)
o Insect pressure (consider a Bt hybrid for replant or
scout and treat where needed)
o Disease pressure (choose replant hybrids with solid
disease resistance and/or scout and treat as needed).
References
Carter, P.R., E.D. Nafziger, and D.R. Hicks. 1992. Effects of
uneven seedling emergence in corn (NCH-36) [Online].
National Corn Handbook Series, Purdue Univ. Coop. Ext.
Service, W. Lafayette, IN 47907.
http://www.agcom.purdue.edu/AgCom/Pubs/NCH/NCH-
36.html
Johnson, R.R. and D.L. Mulvaney. 1980. Development of a
model for use in maize replant decisions. Agron. J. 72: 459-464.
Nielsen, R.L. 2003. Estimating yield and dollar returns from
corn replanting (AY-264-W) [Online]. Purdue Univ. Coop.
Ext. Service, W. Lafayette, IN 47907.
http://www.agry.purdue.edu/ext/pubs/AY-264-W.pdf
®
Roundup Ready is a registered trademark used under license
from Monsanto Company.
®
Select Max is a registered trademark of Valent U.S.A. Corp.
Corn field with poor stand establishment.