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ISU Extension Logo

Northwest Iowa Crop Update Newsletter
by Todd Vagts
ISU Extension Crops Specialist
Counties Served:  Carroll, Calhoun, Crawford, Ida, Monona, Pocahontas and Sac.

[Home][Special Topics][Field Problems][Weather Data][Subsoil H20][PDF Info] [ISU Extension][IA State University]

ISU Extension
Hail Damage Assessment to Soybeans

By Todd Vagts, ISU Extension Crops Specialist

Many fields across the area experienced hail damage from this week’s storms that has led to concerns with corn and soybean stands, survival and their impact on final grain yield.

Questions arise as to:

  • What is and will be the final stand of the soybean field?
  • How healthy is the soybean plant?
  • Given the current stand and defoliation, how much yield impact will the reduced stand have?
  • Should the crop be replanted?
  • What are the replant options for soybeans

Soybean plant

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.
    1. live plants
    2. questionable plants
    3. dead plants
  1. 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 re-grow. 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 re-growth 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

Populations

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. Table 3 shows approximate yield loss due to late planting, beans start to lose yield potential when planted after mid-May in northern Iowa.

 

Table 2. Percent 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 percent of yield at various planting dates

Planting Date

N. Iowa

Late April

100

Early May

96

Mid-May

99

Early June

81

Mid-June

61

Early July

33

Source: Iowa State University

 

Generally, full season adapted varieties can be planted in northern Iowa up until late-June. That would be Late Group II through 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.

 


Todd Vagts
Iowa State University Extension
Field Crops Specialist
1240 D. Heires Avenue 
Carroll, IA 51401 
Office: 712-792-2364; Cell: 712-249-6025;  Fax: 712-792-2366
Email: vagts@iastate.edu  

 

 


For questions or comments please respond to vagts@iastate.edu

This page last updated on 07/21/03

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