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Percent Defoliation Charts for Determining Defoliation Required for Economic Injury to Soybeans

(Excerpted from ENT-13 Insecticide Recommendations for Soybeans 1998, University of Kentucky Entomology Extension Publication ENT-13, Lexington, KY, 1998.)


The ability of soybeans to sustain defoliation without yield reduction varies with the growth of the plant. Under favorable conditions the average percent defoliation figures given in these tables can be used to determine economic injury levels. When the percentage of foliage removed approximates that given in the table for your particular set of variables (cost of treatment, prejected yield, and projected selling price of the beans), treatment should be considered.

For example, if your beans are in the bloom stage, you anticipate the yield will be 35 bushels per acre with a selling price of $8 per bushel and the cost of treating will be $6 per acre, defoliation must be 23 percent or greater to justify treatment.


Pre-bloom (5 to 6 trifoliates)
treatment recommended when defoliation exceeds 35 percent.

Percent Defoliation
Full Bloom Stage - Anticipated Yield 25 bu/A
Cost of Treatment per Acre: $6.00 $8.00 $10.00 $12.00 $14.00
Soybean Value ($/bu)
$6.00 32 37 41 45 49
$7.00 30 34 34 42 45
$8.00 28 32 32 39 42
$9.00 26 30 30 37 40

Full Bloom Stage - Anticipated Yield 35 bu/A
Cost of Treatment per Acre: $6.00 $8.00 $10.00 $12.00 $14.00
Soybean Value ($/bu)
$6.00 27 31 35 38 41
$7.00 25 29 32 35 38
$8.00 23 27 30 33 36
$9.00 22 25 28 31 34

Full Bloom Stage - Anticipated Yield 45 bu/A
Cost of Treatment per Acre: $6.00 $8.00 $10.00 $12.00 $14.00
Soybean Value ($/bu)
$6.00 24 28 31 34 36
$7.00 22 25 28 31 34
$8.00 21 24 27 29 31
$9.00 20 23 25 28 30

Pod Fill Stage - Anticipated Yield 25 bu/A
Cost of Treatment per Acre: $6.00 $8.00 $10.00 $12.00 $14.00
Soybean Value ($/bu)
$6.00 20 24 27 30 32
$7.00 19 22 25 27 30
$8.00 18 20 23 26 28
$9.00 16 19 22 24 26

Pod Fill Stage - Anticipated Yield 35 bu/A
Cost of Treatment per Acre: $6.00 $8.00 $10.00 $12.00 $14.00
Soybean Value ($/bu)
$6.00 17 20 23 25 27
$7.00 16 18 21 23 25
$8.00 15 17 19 21 23
$9.00 14 16 18 20 22

Pod Fill Stage - Anticipated Yield 45 bu/A
Cost of Treatment per Acre: $6.00 $8.00 $10.00 $12.00 $14.00
Soybean Value ($/bu)
$6.00 15 17 20 22 24
$7.00 14 16 18 20 22
$8.00 13 15 17 19 20
$9.00 12 14 16 17 19

Approaching Maturity - Anticipated Yield 25 bu/A
Cost of Treatment per Acre: $6.00 $8.00 $10.00 $12.00 $14.00
Soybean Value ($/bu)
$6.00 34 40 46 52 57
$7.00 31 37 42 47 52
$8.00 28 34 39 44 48
$9.00 26 31 36 40 45

Approaching Maturity - Anticipated Yield 35 bu/A
Cost of Treatment per Acre: $6.00 $8.00 $10.00 $12.00 $14.00
Soybean Value ($/bu)
$6.00 27 33 38 42 46
$7.00 25 30 34 38 42
$8.00 22 27 31 35 39
$9.00 21 25 29 33 36

Approaching Maturity - Anticipated Yield 45 bu/A
Cost of Treatment per Acre: $6.00 $8.00 $10.00 $12.00 $14.00
Soybean Value ($/bu)
$6.00 23 28 32 36 40
$7.00 21 25 29 33 36
$8.00 19 23 27 30 33
$9.00 17 21 25 28 31


This site was created and is maintained by Pat Dillon, Department of Entomology, University of Kentucky, S-225 Agricultural Science Ctr North, Lexington, KY USA  40546-0091 (phone: 859/257-3571). Please send questions or suggestions to: pdillon@uky.edu