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East-Central and Southeast Iowa Crop Information

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EVALUATING HAIL DAMAGE ON SOYBEANS

  1. Check the number of live plants per foot of row. Lay a tape in the row and dig up all plants in a 3 foot or more length. For drilled beans, two rows could be dug. Repeat several times over the field, keeping track of the live plants per foot of row.

  2. Examine plants carefully and separate into three piles.

  3. Add the number of live plants and one-half the number of questionable plants and divide by the length of row to get the number of live plants per foot of row. Plants cut off below the cotyledons (thick bottom seed leaves) will not regrow. If plants are broken off above the cotyledons, there is a bud in the axil between the cotyledon and stem and between the unifoliate and trifoliate leaves and the stem which will produce new growth. It takes about 4-7 days to see regrowth on soybeans after hail.

Beans tend to branch, so the number of plants per acre can vary greatly with moderate effect on yield. If the stand loss is fairly uniform, it generally takes a population of less than 75,000 plants per acre to pay to replant in mid to late May and less than 50,000 - 60,000 in mid-to-late June. However, if most of the remaining stand is made up of "questionable" plants, it may pay to replant with a higher population.

Table 1. APPROXIMATE NUMBER OF PLANTS PER FOOT OF ROW TO GIVE VARIOUS POPULATIONS PER ACRE

----------------------------Population----------------------------

Row Width

150,000

125,000

100,000

75,000

50,000

36 - 38

10.6

8.8

7.1

5.3

3.5

30

8.6

7.2

5.7

4.3

2.9

20

5.7

4.8

3.8

2.9

1.9

15

4.3

3.6

2.9

2.2

1.4

10

2.9

2.4

1.9

1.4

1.0

7

2.0

1.7

1.3

1.0

0.7

 

Table 2 shows the yields that may be expected when populations are thinned at various stages of development. Beans start to lose yield potential when planted after mid May in central Iowa. Table 3 shows average yield that can be expected from delayed planting.

 

TABLE 2. PER CENT OF SOYBEAN YIELD AT VARIOUS POPULATIONS WHEN THINNED AT VARIOUS STAGES OF DEVELOPMENT

Thinned at

Final Stand

VC

V3

V6

50,000

92

85

74

75,000

98

99

92

100,000

100

107

98

125,000

99

102

100

150,000

100

101

100

75,000 w/ 1 ft. gaps

97

97

89

75,000 w/ 2 ft. gaps

92

92

86

Source: University of Minnesota

 

TABLE 3. APPROXIMATE PER CENT OF YIELD AT VARIOUS PLANTING DATES

Planting Date

Northern

Central

Southern

Iowa

Iowa

Iowa

Late April

100

96

98

Early May

96

100

100

Mid-May

99

96

98

Early June

81

93

89

Mid-June

61

59

82

Early July

33

45

47

Source: Iowa State University

 

Generally, full season adapted varieties can be planted in central Iowa up until mid-June. In central Iowa, that would be Late Group II until the end of June and then an Early Group II in July .

A small amount of leaf area loss, especially at early stages of growth does not usually result in much yield loss. Hail loss estimates on beans are complicated by bruising and the effect of lower stem bruises is hard to evaluate. Deep bruises can result in lodging of the soybeans later in the season.

Prepared by Jim Fawcett and Virgil Schmitt, ISU Extension Field Specialists - Crops, 6/2001.

 

If you have any questions, please feel free to contact the Iowa State University Extension Office.


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Last Update: June 12, 2001
Contact: Virgil Schmitt vschmitt@iastate.edu


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