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:

Planter Speed
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.
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.
Frost
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.
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.
Seeds hollowed out. Seed corn maggot or wireworm. Look for evidence of the pest to confirm.
Inter-plant competition for solar radiation, water and nutrients
Low soil fertility
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.
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

Corn Replanting

Steps in the process

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

Step 2: Evaluate plant health

Step 3: Assess the unevenness of stands

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

Step 5: Calculate replanting costs

Step 6: Factor in risks of replanting

Further Reading