Corn Replanting

Originally written February 1, 2006 | Last updated March 14, 2014

UWEX Re-planting / Late planting - A3353

Steps in the process

  1. Determine plant population
  2. Evaluate plant health 
  3. Assess the unevenness of stands
  4. Compare the yield of a reduced stand to that of a replanted stand
  5. Calculate replanting costs
  6. Factor in risks of replanting

Late-planting

Step 1: Determine plant population (use 1/1000 acre)

Row Spacing Row Length
10" 52' 3"
15" 34' 10"
19" 27' 6"
30" 17' 5"
36" 14' 6"
38" 13' 9"
40" 13' 1"

Step 2: Evaluate plant health 

Troubleshooting emergence problems early is critical in identifying solutions and developing successful replant plans, if needed. Here's a list of a few common things to look for if you encounter an emergence problem in corn this spring.

A corn seedling stalk is split to show the growing point, the twisted whorl of leaves, and the bacterial soft rot infection (the brown discoloration in the of the stem).

Healthy corn has a creamish-white appearance to the roots and growing point. Dark, discolored areas are typical symptoms of seedling diseases problems. As corn starts to emerge, growers should carefully inspect seedlings for symptoms of disease, especially in lower lying areas of fields where ponding and saturated soils are more likely. It is more difficult to diagnose disease damage on plants that also show abnormal growth caused by cold soil conditions or by crusting of the soil surface. So, it is best to check these seedlings very closely for dark brown or soft areas on seedling roots and shoots. Any discoloration indicates a problem that could worsen.

Seed rot or seed with low vigor: Symptoms are a poorly developed radicle (root) or coleoptile. The coleoptile tip is  brown or yellow. Seeds and seedlings that are brown in color, are soft and fall apart easily while digging may be dead or dying.

Seed and seedling diseases: Pythium and Fusarium are common fungi that attack plants and cause these damping-off or seedling blight symptoms under wet, cool conditions. Seeds and seedling roots or shoots that have white to pinkish mold growing on them will likely die.  

Step 3: Assess the unevenness of stands

Some factors that cause spatial and temporal plant variability:

  1. Planter Speed
  2. No seed present. May be due to planter malfunction or bird or rodent damage. The latter often will leave some evidence such as digging or seed or plant parts on the ground.
  3. Skips associated with discolored and malformed seedlings. May be herbicide damage. Note depth of planting and herbicides applied compared with injury symptoms such as twisted roots, club roots, or purple plants.
  4. Frost
  5. Seed has swelled but not sprouted. Often poor seed-to-soil contact or shallow planting- seed swelled then dried out. Check seed furrow closure in no-till. Seed may also not be viable.
  6. Coleoptile (shoot) unfurled, leafing-out underground. Could be due to premature exposure to light in cloddy soil, planting too deep, compaction or soil crusting, extended exposure to acetanilide herbicides under cool wet conditions, combinations of several of these factors, or may be due to extended cool wet conditions alone.
  7. Seeds hollowed out. Seed corn maggot or wireworm. Look for evidence of the pest to confirm.
  8. Inter-plant competition for solar radiation, water and nutrients
  9. Low soil fertility
  10. Saturated and/or cool soils: May be due to soil moisture and temperature variability within the seed zone. Poor seed to soil contact caused by cloddy soils. Soil crusting. Other conditions that result in uneven emergence already noted above, including feeding by various grub species.
  11. Drought

Note patterns of poor emergence. At times they are associated with a particular row, spray width, hybrid, field or residue that may provide some additional clues to the cause. Often two or more stress factors interact to reduce emergence where the crop would have emerged well with just one present. Also, note the population and the variability of the seed spacing.

Don't forget that corn may take up to 3 to 4 weeks to emerge when soil conditions are not favorable (e.g. temperatures below 55 degrees F, inadequate soil moisture). As long as stands are not seriously reduced, delayed emergence usually does not have a major negative impact on yield. However, when delayed emergence is associated with uneven plant development, yield potential can be reduced.

Spatial Plant Variability - Distribution of plants in a row

Handout of plant spacing variability

  • Currently receiving a lot of press. Claims of 20% yield increases if spacing variation = 0
  • Spacing variability affects yield when spacing standard deviation > 4.7 inches
  • Further reading:
    Lauer, Joseph G. and Mike Rankin. 2004. Corn Response to Within Row Plant Spacing Variation. Agronomy Journal 96:1464-1468.

Temporal plant variability - eveness of emergence

One way to simulate eveness of stand and its effect on yield is to clip (or 'set back') plants at various stages of growth by clipping all of the above gound leaves on the plant. Corn grain yield is affected when 50% of the plants are clipped.

However, when 100% of the plants are clipped little impact on yield is observed in most years.

Another method that simulates the effect of emergence on grain yield is planting seed into a growing stand at various growth stages (see NCR344).

Step 4: Compare the yield of a reduced stand to that of a replanted stand

Expected corn grain yield for various planting dates and harvest populations in Relative Maturity zones of 70 to 95 days. Figures for shorter-season hybrids are in italics.  The actual Relative Maturities of short-and full-season hybrids vary with location and soil type.  

Harvest Planting date
population April 20 May 1 May 10 May 20 June 1 June 10 June 20
  full short full short full short full short full short full short full short
  percent of expected yield
36000 96 82 100 89 97 89 86 82 63 65 39 46 5 18
34000 95 81 99 88 96 88 85 81 63 65 39 46 5 18
32000 94 80 98 87 95 87 85 80 62 64 38 45 5 18
30000 93 79 97 86 94 86 83 79 61 63 38 45 5 18
28000 91 78 95 85 92 84 82 78 60 62 37 44 5 18
26000 89 76 93 83 90 83 80 77 59 61 37 43 5 17
24000 87 75 91 81 88 81 79 75 58 59 36 42 5 17
22000 85 73 89 79 86 79 76 73 56 58 35 41 5 16
20000 82 70 86 76 83 76 74 70 54 56 34 40 4 16
18000 79 68 83 74 80 73 71 68 53 54 32 38 4 15
16000 76 65 80 71 77 70 69 65 50 52 31 37 4 15
14000 73 62 76 67 74 67 65 62 48 49 30 35 4 14
12000 69 59 72 64 70 64 62 59 46 47 28 33 4 13
10000 65 55 68 60 66 60 58 56 43 44 27 31 3 13
 

Expected corn grain yield for various planting dates and harvest populations in Relative Maturity zones of 95 to 115 days. Figures for shorter-season hybrids are in italics.  The actual Relative Maturities of short-and full-season hybrids vary with location and soil type.  

Harvest Planting date
population April 20 May 1 May 10 May 20 June 1 June 10 June 20
  full short full short full short full short full short full short full short
  percent of expected yield
36000 96 91 99 95 95 93 85 87 63 71 40 55 8 32
34000 97 92 100 96 96 94 85 87 63 72 40 56 8 32
32000 97 92 100 96 96 94 86 87 63 72 40 56 8 32
30000 96 92 100 96 96 94 85 87 63 72 40 56 8 32
28000 96 91 99 95 95 93 84 86 63 71 40 55 8 32
26000 94 89 97 93 93 92 83 85 62 70 39 54 8 31
24000 92 87 95 91 91 89 81 83 60 68 38 53 7 31
22000 89 85 92 88 89 87 79 81 58 66 37 51 7 30
20000 86 82 89 85 85 84 76 78 56 64 36 49 7 29
18000 82 78 85 81 82 80 72 74 54 61 34 47 7 27
16000 78 74 80 77 77 76 68 70 51 58 32 45 6 26
14000 73 69 75 72 72 71 64 65 47 54 30 42 6 24
12000 67 64 69 66 67 65 59 60 44 50 28 38 5 22
10000 61 58 63 60 60 59 54 55 40 45 25 35 5 20

Step 5: Calculate replanting costs

Step 6: Factor in risks of replanting

  • Soil fertility
    • Starter fertilizer may be needed with full-season hybrids planted late
  • Pest control
    • weeds
    • insects
    • diseases
  • Weather influences

Further Reading

Grain Crop Alternatives

Corn Replanting or Late-Planting Decisions UWEX Bulletin A3353

Uneven emergence in corn NCR344


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