REVISED: May 24, 2024 (originally published May 8, 2019 by authors Roger Elmore, Jenny Rees and Robert Klein) According to the USDA-NASS report, 35% of Nebraska’s corn had been planted as of May 5, similar to 38% last year but behind the five-year average of 47%. Emergence was at 2%, similar to last year but behind the 9% average. The April 26 report indicated 16% of corn had been planted compared with 15% last year, and 23% for the five-year average. Corn already planted has no doubt been subjected to cool soil temperatures. Corn planted into soil with temperatures below 50⁰F may experience difficulties or fail to emerge. Bob Nielsen, Purdue University corn specialist, covered these issues to some depth ― no pun intended ― in this article. -->

Recent flooding events beginning May 20-21, 2024 in portions of the state have some concerned about the need to replant corn when waters recede. It’s important to assess potential recovery before making replant decisions. This information pertains regardless of any disaster causing a potential replant situation (flooding, hail, frost damage, etc.) This information is revised from articles Lori Abendroth and Roger Elmore wrote several years ago.

Table 1. Row length necessary to equal 1/100th and 1/1000th of an acre in various row widths.

Row Width (inches)	Row length in feet to equal 1/100th of an acre	Row length in feet to equal 1/1000th  of an acre
15	348’6”	34’10”
20	261’4”	26’2”
30	174’3”	17’5”
36	145’2”	14’6”
38	137’7”	13’9”

1. Wait five to seven days after emergence begins, then determine the current plant population.
   
   • Dig in the gaps to check the status of “missing” plants.
   • Scout in a zigzag pattern across the field to best represent its overall condition, including both better and worse areas.
   • To estimate surviving plant stands, count plants in at least three areas in affected fields. Consider increasing your accuracy by counting plants in 1/100 of an acre in contrast to just those in 1/1000 of an acre. Use Table 1 to determine the length of row necessary to achieve either a 1/100 or a 1/1000 of an acre sample. Multiply by either 100 or 1000 (depending on which area you counted) to determine the number of live plants per acre.
   • In the counted area, estimate whether severely injured plants will survive by checking the growing point and recovery. If the growing point is discolored and soft, the plant won’t survive. If it is firm and new green growth is emerging from it, it will most likely survive.
   • Consider plant stand uniformity (if there is uneven emergence). If uneven emergence is row to row, that is, most rows have emerged but some are not, replanting will likely not increase yield significantly.
   • If the delay in emergence is less than two weeks between the early and late-emerging plants, replanting may increase yields, but by only 5% or less. Replanting would likely not be economical. Yet, if one-half or more of the plants in the stand emerge three weeks later than the initial plant emergence, replanting may increase yields by about 10%.
2. Calculate the expected yield from the existing stand using Table 2.
   • Table 2 summarizes planting date and plant population (final stand) relationships. Please see the examples below Table 2 for an explanation on using this table.
   For example, if the original planting date was April 30, a population of 35,000 plants/acre is expected to provide maximum yield, based on Table 2. If the population is only 20,000 plants/acre, yield potential is 89% of the maximum for the April 30 planting date. Replanting on May 20 at 35,000 plants/acre will result in approximately 87% of the maximum yield. Compare the replanted crop to the original crop which was planted on April 30 and now has a population of 20,000 plants/acre, and consider the costs of replanting. Expected yields are 89% for retaining the old stand versus 87% for a replant. -->
   • If several 4- to 6-foot gaps occur within the row, yields will be reduced an additional 5% relative to a uniform stand. Stand gaps of 16 to 33 inches will only reduce yield by 2%.
   • Ensure good weed management to aid for less competitive stands.
   • Remember, there is no guarantee of getting a good stand with replanting. Insect and disease pressure may be greater in replanted fields.
   • Estimate replant yield with Table 2. Use planting date and target plant population to estimate the yield potential of the replanted field.
   • Remember the concept of planting windows. (See CW articles with Nebraska data, historical Nebraska data, and Corn Belt data.) With that in mind, consider that the yield reductions listed in Table 2 may be greater than what may actually occur in 2024. Hybrids and genetics have improved and weather variation has increased since this table was developed. Anymore, an early to mid-May planting may result in full yield potential in some years.
   NOTE: For example, in 2022, when widespread hailstorms impacted south and east-central Nebraska on June 14, corn wasn’t replanted till the end of June. In spite of sharing expected yields would be around 50% of maximum, yields of 200+ bushels/acre were still achieved (even with most of the corn being killed prematurely by frost). The yields may be due to that specific year, but genetics and environmental conditions have changed the optimal planting windows for corn. There is need for additional research using today’s hybrids and weather variability.  
3. Estimate replanting costs.
   • The cost of replanting a field is often the deciding factor.
   • Make sure to include tillage, seed, fuel (for tillage and planting), additional pesticides, labor, etc. Don’t forget that the chance of fall frost is higher for late-planted corn.
   • Check with your seed dealer to see what hybrid seed is available and if there is any rebate or price reduction for replant situations. In general, there is not much of a reason to switch to earlier-season hybrids until early June. (See this CW article on when to change hybrids.)

Table 2. Relative yield potential of corn by planting date and population.

Population (Plants/Acre)	Planting Date April 20–May 5 % Max Yield	Planting Date May 5–15 % Max Yield	Planting Date May 15–25 % Max Yield	Planting Date May 25-June 5 % Max Yield	Planting Date June 5–15 % Max 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
With where we’re sitting today, if there are 25,000 plants per acre remaining and the field was initially planted on April 25, according to Table 2, the expected yield would be 95% of maximum. If you couldn’t replant until May 30, it may be better to leave the original stand than try to plant May 30 at 30,000 seeds per acre with an expected yield of nearly 69%. If planting occurred on May 20 prior to this flooding event and a stand of 25,000 plants per acre remained with a yield potential of 83% of maximum, if you couldn’t replant until May 30, according to this chart, an expected yield potential would be nearly 69% of maximum yield. Consider your individual field situation and cost of replanting. Remember, there is no guarantee of getting a good stand with replanting and that late season insect and disease pressure may be greater in replanted fields. Also note that the yield reductions listed in this table may be greater than what actually occurs in 2024. Note: Values based on preliminary Iowa research and modeling; 100% yield potential is estimated to occur with 35,000 plant population and early planting. From: Iowa State University Extension, Corn Field Guide, 2nd edition. CSI 001. 2013.

Acknowledgment

This article was adapted from an article by Lori Abendroth and Roger Elmore, Iowa State University, May 2010, as well as an article by Roger Elmore and Lori Abendroth on May 20, 2005.

Abendroth, Lori, and Roger Elmore. 2010. Replant Checklist. Iowa State University Extension.

Nielsen, R. L. 2019. Emergence failure of corn. Purdue University

USDA-NASS. 2019. Nebraska Crop Progress and Condition. -->