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

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 Date	Low 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

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.

(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.

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.