Keep my initial corn stand or replant it?

Dug up corn plant that hasn’t emerged.

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

Background: In Colfax, Dodge, and Washington counties, corn emergence and plant population in some fields planted from April 13-17 are less than ideal. Fields were planted into dry soil during warm weather. Then, rain and cold weather set in from April 18 through April 21 that created stressful conditions (Table 1).

Table 1. Daily temperature and rainfall from April 13-21, 2016 in Fremont, NE (Source: High Plains Regional Climate Center)
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

Answer:

First, you need to 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 determine the plant population from two adjacent rows in each of the 10 locations. Make a note at each location about the size of the gaps within the rows. 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 are very unlikely to develop normally. Refer to last week’s Crop Watch article for more information.

Table 2. Example of information to record while in the field to help guide your decision to keep it or replant it. For 30” rows, 1/1000 of an acres is 17 ft 5 inches.
Locations (1-10)	Row 1: (1/1000 of an acre)	Adjacent Row (Row 2)	Average	Size of Gap (ft)	Potential emerging plants
1	17	22	19.5	2	2
2	14	14	14	3	4
3-10	…	…	…	…	…
Average			19	2	2

Next, we 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. Note: Values based on preliminary research and modeling. (Source: Iowa State University)
	Planting Date
	April 20 – May 5	May 5 – 15	May 15-25	May 25 – June 5	June 5 – June 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
*Gaps: 1.3 to 2.8 ft gaps = 2% additional yield reduction, 4- to 6-ft gaps = 5% additional yield reduction, emergence of less than 2 weeks between early and later emerging plants, <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 35k. 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). 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 to acre to emerge this week.

Now let us assume you have an average of 15,000 plants per acre with 4- to 6-ft gaps, so expect roughly 76% (81% – 5% = 76%) of maximum yield. In this case replanting prior to May 25 could get us 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 use 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 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 to 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. Lastly, before you decide to terminate your poor stand, remember to call your crop insurance agent and have an adjustor visit the field.

In most cases, you are often better off keeping your initial stand. With 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.

Let’s review the steps in making a decision to keep it or replant it again:

In the field… determine current plant population, length of in-row gaps and evaluate non-emerged plants for possibility of emergence.
From your pickup… lookup yield potential of replanted corn versus current corn plant population using the table provided.
From your desk… evaluate the cost to replant and make a plan on how you are going to terminate the existing stand if needed.
From your phone… contact you crop insurance agent and have an adjustor visit the field before terminating the initial standand make sure seed is available from your seed supplier.

Your local Nebraska Cropping Systems Extension Educators, Nathan Mueller and Aaron Nygren