2Assessing Delays in DevelopmentDelays in corn seedling development can also have a negativeimpact on yield (Carter et al., 1992).• If surviving plants are uniform (within 2 leaf stages ofeach 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®BrandHybridFamilyFinal Stand (plants per acre in thousands)20 22 24 26 28 30 32 34 36Percent of Optimum YieldP0912 92 95 98 99 100 99 97 96 94P1319 96 98 99 100 100 99 99 98 97P1498 89 92 95 97 98 100 100 98 97P2088 94 95 97 99 100 100 100 98 96Average 93 95 97 99 100 100 99 98 96Source: 2006-2012 DuPont Pioneer population trials conductedpredominantly at research stations near Union City, TN, Cairo, GA,Kinston, NC, and Princeton, IN.Worksheet 1: Gross Returns Current CropComplete the following to estimate gross $ returns on currentcrop.Worksheet 1Step 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 CropStep 7 x Step 8 ____________Worksheet 2: Gross Returns Replanted CropComplete the following to estimate gross $ returns onreplanted crop assuming uniform stands and even emergenceof replanted corn in the next column.Worksheet 2Step 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 CropStep 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-OtherStep 8: Expected Gross Returns Above Added CostsReplanted CropStep 5 - Step 6 - Step 7 ____________Table 5. Influence of planting date on optimum corn yield forvarious regions of the U.S. assuming optimum plantpopulations. a,bPlantingDateRegionMid-West Mid-South------- % of maximum yield ----------March 20 --- 93March 30 --- 95April 1 99 97April 10 100 97April 20 100 98April 30 97 96May 9 93 93May 19 86 86May 29 78 82June 8 67 68aSource: Emerson Nafziger, Eric Adee, and Lyle Paul, Univ. ofIllinois; Jason Kelley, Univ. of Arkansas, and Erick Larson,Mississippi State University.bMid-South data generated from plots grown under irrigation in MSand AR using hybrids containing Bt genes. Percentages may notaccurately reflect yield levels for low yield potential drylandenvironments. Data collected from 2008-2010 in AR and from2009-2011 in MS.
3Making the DecisionCompare the expected returns of the current crop (worksheet1) and the expected returns of the replanted crop (worksheet2). Are the returns to replant higher? If yes, the decisionbecomes easier to make. If Mother Nature cooperates andhistoric yield trends hold true, you should be dollars ahead.By replanting and establishing a consistent stand, you alsoeliminate weed control challenges in thin stands.Unfortunately, reduced stands are never consistent across thefield and large pockets of extremely thin stands normallyoccur. This is where the “art” of farming overrides thescience. Will these field areas produce challenges for weedcontrol? How much additional yield loss will occur due toextremely thin areas? Can only the pockets be replanted?How will harvest of the field be affected?Even if the calculation demonstrates that costs are greaterthan or equal to the potential gain, some growers may stilldecide to replant. For those growers the irritation of startingout with a poor stand and limited crop potential simplyoutweighs the economic advantage of keeping the stand.Although appropriate for “close calls”, emotion in thisdecision can be costly and should generally be avoided.Other ConsiderationsBelow is a list of other items to keep in mind when making areplant decision:• A thin stand is better than no stand at all. Remember tofinish planting the remainder of your fields (for cropproduction with the same planting window) beforereplanting a field.• It’s important to remove the existing thin stand beforereplanting. Patching in additional seeds next to a thinstand is rarely beneficial and creates challenges due todifferences in spacing and timing of crop growth anddevelopment (e.g., competition between plants,pollination timing and harvest maturity timing). Removingthe remaining stand can be accomplished by:o Mechanical tillageo Herbicide applications. Where the original stand isRoundup Ready®, the most efficacious option islikely to be Select Max®at 6 oz/acre, 6 days prior toreplanting, especially if translocation is needed onvery small corn and corn that is barely emerged. Besure to check the label before applying. Othertreatment options that have proven efficacious andthat allow immediate plant back include paraquatmixed with linuron, diuron, or metribuzin. Metribuzinis only labeled for corn plant back in some states.Check labels for more specific information. Alsocheck with your local chemical supplier or ExtensionService professional for specifics on product ratesand restrictions.• If replanting will occur a little on the late side of the“normal window”, consider the challenges this willcreate. Additional management may be required toprevent or minimize yield-limiting factors such as:o Heat stress during pollination (timely irrigationneeded where possible)o Insect pressure (consider a Bt hybrid for replant orscout and treat where needed)o Disease pressure (choose replant hybrids with soliddisease resistance and/or scout and treat as needed).ReferencesCarter, P.R., E.D. Nafziger, and D.R. Hicks. 1992. Effects ofuneven 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.htmlJohnson, R.R. and D.L. Mulvaney. 1980. Development of amodel for use in maize replant decisions. Agron. J. 72: 459-464.Nielsen, R.L. 2003. Estimating yield and dollar returns fromcorn 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 licensefrom Monsanto Company.®Select Max is a registered trademark of Valent U.S.A. Corp.Corn field with poor stand establishment.