Q and A: Should I Keep My Initial Corn Stand or Replant?

Q and A: Should I Keep My Initial Corn Stand or Replant? May 13, 2016


Question: Should I keep my initial corn stand or replant it?

Corn leafing out below ground
Figure 1. Non-emerged corn plant damaged from stressful conditions.

Background

In counties north of the Platte River in east central Nebraska, corn emergence and plant population in some fields planted April 13-17 are less than ideal.  Fields were planted into dry soil during warm weather. Then, rain and cold weather set in April 18-21, creating stressful conditions (Table 1). This article examines the question faced by a grower this week in east central Nebraska.

Answer

First, determine your current plant population across the entire field, not just the best and worst areas. We would suggest taking the plant population in 10 random locations across the field and determining the plant population from two adjacent rows in each of the 10 locations. Make a note at each location for the size of gaps (space between plants in the row).  Depending on the field and conditions, it may be helpful to dig up plants that haven’t emerged to determine if they still have a chance of emerging. Determining if plants have a chance to emerge is a judgement call; plants that corkscrewed or leafed out underground (Figure 1) are very unlikely to develop normally. For more information refer to last week’s Crop Watch article, Planting Delays? It's too Early to Consider Switching Hybrids or Moving to Soybeans.

Table 1. Daily temperature and rainfall from April 13-21, 2016 in Fremont*
Calendar DateLow Temp (F°)High Temp (F°)Rainfall (inches)
April 13 27 69 0
April 14 44 78 0
April 15 48 76 0
April 16 51 77 0
April 17 58 73 0
April 18 52 73 0.27
April 19 41 56 0.70
April 20 41 59 0.48
April 21 49 55 1.30
*Source: High Plains Regional Climate Center
Table 2. Example of information to record while in the field to help guide your decision to keep or replant.
Locations (1-10)No of Plants Row 1:
(1/1000 of an acre*)
No of Plants
Adjacent Row (Row 2)
No of Plants
Average
Size of Gap (ft)Potential Emerging Plants
Location 1 17 22 19.5 2 2
Location 2 14 14 14 3 4
Locations 3-10 Complete filling out table as in example for first two rows.
Average 19 2 2
*For 30-inch rows, 1/1000 of an acre is 17 feet 5 inches.
Note: Values are based on preliminary research and modeling. (Source: Iowa State University)

 

Next, use the 2010 Iowa State University relative yield potential of corn by planting date and population (Table 3) to determine the yield potential of the current stand versus the potential of a replanted stand.

Table 3. Relative yield potential of corn by planting data and population.
Remaining Stand
(plts/acre)
Planting Date
April 20 – May 5
Planting Date
May 5 – 15
Planting Date
May 15 – 25
Planting Date
May 25 – June 5
Planting Date
June 5 – 15
Percent of Maximum Yield
45,000 97 93 85 68 52
40,000 99 95 86 69 53
35,000 100 96 87 70 54
30,000 99 95 86 69 53
25,000 95 91 83 67 51
20,000 89* 85 77 63 48
15,000 81* 78 71 57 44
10,000 71* 68 62 50 38
Note: Values are based on preliminary research and modeling. (Source: Iowa State University)
*Gaps: 1.3- to 2.8-foot gaps = 2% additional yield reduction; 4- to 6-ft gaps = 5% additional yield reduction
Less than 2 weeks between early and later emerging plants, less than 5% additional yield reduction.

(We need to take this information with a little grain of salt since it is data from Iowa and likely represents more irrigated conditions here given the relative yields table shows 100% of maximum yield with 35,000.)

After the additional rain this this week, we won’t likely get much corn planted before May 15.  Therefore, we are looking at 87% of maximum yield with replanting corn (Table 3, gray area). In the example where we have an average of 19,000 plants per acre with 2-foot gaps, we would expect roughly 86% (88% - 2% = 86%) of maximum yield. In this situation, it is unlikely there will be much of an advantage to replanting. There is also the potential for another 2,000 plants per acre to emerge this week.

Now, let us assume you have an average of 15,000 plants per acre with 4- to 6-foot gaps. The table indicates you could expect roughly 76% (81% - 5% = 76%) of maximum yield; however, by replanting (Table 2) you might expect 87% of maximum yield. We do want to point out that you don’t lose 17% of your maximum yield between May 25 and May 26; so take this guide with a little grain of salt!  If replanting occurs after May 25, we may only expect to get 70% of maximum yield and we are into the crop insurance late planting period from May 26 to Jun 14 where we lose insurance coverage by 1% per day off of your production guarantee.

Replant coverage with crop insurance (multi-peril) for 2016 is 8 bushels times the price election ($3.86) or roughly $31/acre and replant seed coverage from seed suppliers could be 50-100%. Be sure to evaluate the cost of tearing up the existing stand and starting over and make a plan on how you are going to terminate the existing stand. No-tillers may not want to use tillage to terminate the stand so be sure to evaluate your herbicide options. (See June 2014 article, Replant Options Following Corn Pre-Emergence Herbicide Applications.)


Extension Educator Nathan Mueller discusses corn stand issues on the May 20 Market Journal.

Lastly, before you decide to terminate your poor stand, remember to call you crop insurance agent and have an adjustor visit the field.

In most cases, you are often better off keeping your initial stand. With a less than an ideal corn stand you should strongly consider using a herbicide with good residual activity in your postemergence program to help suppress weeds.

Summary

Let’s review the steps in deciding whether to keep or replant a field :

  1. In the field… determine current plant population and length of in-row gaps. Evaluate non-emerged plants for possibility of emergence. (Table 2 is shows how this data might be captured.)
  2. From your pickup… look up yield potential of replanted corn versus current corn plant population using the table provided. (Table 3)
  3. From your desk… evaluate the cost to replant and make a plan on how you are going to terminate the existing stand if needed.
  4. From your phone… contact your crop insurance agent and have an adjustor visit the field before terminating the initial stand. Also, make sure seed is available from your seed supplier.
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