Corn planting has progressed faster and earlier than normal in most areas this year. Many farmers have finished planting corn and are turning their attention to soybean planting. As corn plants emerge stand evaluations and assessments will be made on fields. For guidelines on assessing plant population in corn fields, see UWEX Bulletin A3353 "Corn Replanting or Late-Planting Decisions" (http://cf.uwex.edu/ces/pubs/pdf/a3353.pdf).

Nearly every farm has a field with poor plant emergence due to weather conditions, pests and/or crusting. Evaluating stands is a six-step process:

Determine plant population of the field (use 1/1000^th acre)
Evaluate plant health: if health is suspected count as ½ plant
Assess the uneveness of stands see http://learningstore.uwex.edu/Uneven-Emergence-in-Corn-P172C0.aspx
Compare the yield of a reduced stand to that of a replanted stand
Calculate replanting costs
Factor in risks of replanting

The following tables are provided for southern and northern Wisconsin. These tables provide data on the impact of planting date and plant population on corn grain yield. Also you can use these tables for corn stand assessments in completing step #4 above – Comparing 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 95 to 115 days (i.e. south and south central Wisconsin)
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
Figures for shorter-season hybrids are in italics. The actual Relative Maturities of short-and full-season hybrids vary with location and soil type.

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