Corn replant checklist

Encyclopedia Article

From emergence to 3rd leaf stage is the time when farmers should be out in their fields assessing stands to determine if replanting is necessary. Replant decisions are never easy and are ultimately determined by which decision provides the greatest net income. Each field will have its own set of circumstances that will influence the decision. Remaining stand level and likely replant date will be the key issues.

Stand assessment is important to determine if there is economic damage to young plants. Young corn plants (<5th leaf stage) can tolerate significant leaf damage and loss and yet remain viable and produce new leaves. This is because the growing point remains below the soil surface until approximately the 6th leaf stage.

Attempts to "thicken" stands by interseeding directly into an existing stand generally result in additional complications. Larger plants compete strongly for space, water, and nutrients and complicate subsequent management decisions. Thus, it is always recommended that if a replant is warranted, destroy the original stand and start over. If the original stand is adequate, leave it alone and be willing to accept it as is.

Another major consideration that goes hand-in-hand with making a replant decision is whether or not a hybrid change is needed or perhaps a change to an alternate crop such as soybean. Switching to an earlier maturing hybrid can be done at any time if so desired. Prior to Une 1, is is recommended to stay with originally chosen well adapted hybrid maturities. However, full season hybrid maturities less consistently reach physiological maturity compared to short season hybrids, especially when planting is delayed past June 1.

Checklist

1. Determine the remaining plant population. 

Calculate the plant population in several "random" areas in the affected part of the field to help estimate the existing population. Do not be tempted to go to the worst area and start counting there, ignoring the better parts of the affected area. The idea is to characterize the field as best you can. Try to make a zig-zag pattern across the field to best represent its overall condition.

To estimate surviving plant stands, you will want to count plants in at least three places in the affected field. Your accuracy will be greater if you count plants in 1/100 of an acre. Use Table 1 to determine the length of row necessary to achieve 1/100 of an acre. You can also measure 1/1000 of an acre; more than three measurements should be taken though to increase accuracy.

Table 1. Total linear feet of row required to make 1/1000 of an acre at different row widths.

Row spacing (inches) Row length for 1/1000 acre (linear feet)
7 74.7
10 52.3
15 34.8
20 26.1
22 23.8
28 18.7
30 17.4
32 16.3
34 15.4
36 14.5
38 13.8

Determine whether the population you counted will completely survive. Were there plants included in the count that appear to be damaged due to insects, disease, frost, hail, flooding, soil crusting, etc? You will need to estimate whether any plants are severely injured or will soon die. These considerations may reduce the number of plants in the field that will actually contribute to final yield.

2. Consider plant stand uniformity (if there is uneven emergence).

  • If uneven emergence is row to row, that is, most rows are emerged but some are not, replanting will likely not increase yield.
  • 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%. Several tools are available for estimating yield loss from variable stands, such as the worksheet found in Tools to calculate yield loss from uneven heights.

3. Calculate expected yield from the existing stand.

Table 2. Corn grain yield response to planting date and plant population using the APSIM crop model and validated using field research trails rom seven Iowa locations.

 

Seeding Rate

15,000

20,000

23,000

28,000

31,000

35,000

39,000

44,000

47,000

52,000

Final Stand

13,000

17,000

20,000

24,000

27,000

31,000

34,000

38,000

41,000

45,000

 Planting Date

……………………………….… Percent of maximum yield ………..…………………………

15-Apr

59

73

85

94

99

100

98

95

95

95

25-Apr

58

72

83

92

98

99

97

96

97

96

5-May

56

70

81

90

96

99

98

97

99

96

15-May

54

66

77

85

92

95

95

95

94

94

25-May

48

60

69

77

83

87

88

89

88

85

1-Jun

42

52

61

68

72

76

78

78

78

76

15-Jun

29

35

41

45

48

51

52

52

50

48

25-Jun

18

22

25

28

29

30

30

30

28

26

(Guide to Iowa Corn Planting, CROPR 3161, 2019)

The potential yield associated with the original planting date with the actual population will give a fair estimate of the actual yield of the problematic field. Table 2 summarizes planting date and plant population (final stand) relationships. For example, if the original planting date was April 15, a population of 31,000 plants/acre is expected to provide maximum yield. If the population is only 20,000 plants/acre, yield potential is still 85% of maximum.

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%.

4. Estimate replant yield. Planting date and target plant population are used to estimate the yield potential of the replanted field. Use Table 2 for this too. Replanting on May 25 at 35,000 seeds/acre will result in approximately 87% of maximum yield. Compare the replanted crop to the original crop which was planted on April 30 which has an existing 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. Remember also that there is no guarantee of getting a good stand with replanting. Insect and disease pressure may also be greater in replanted fields.

5. Estimate replanting costs. The cost of replanting a field is often the deciding factor. Costs include tillage, seed, fuel (for tillage and planting), additional pesticides, labor, etc. Moreover, the chance of fall frost is higher for late-planted corn. Check with your seed dealer to see what hybrid seed (shorter maturity) is available and if there is any rebate or price reduction for replant situations.

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