Appendix G. European Corn Borer
Economic Threshold Calculations
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Pub 811:
Agronomy Guide > Appendices
> Appendix G. European Corn Borer Economic Threshold Calculations
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811: Agronomy Guide for Field Crops
Use these calculations to estimate if it is economic to
treat a non-Bt field with an insecticide. See European
corn borer
Univoltine Strain (for areas where
there is one generation of ECB per year)
A. % shot-holed plants ___________ = plants
with shot-holes ÷ total plants checked
Unfurl one of the shot-holed plants from each location and look for
larvae.
B. Larvae per plant ___________ = number of live larvae
per unfurled plant x (A)% shot-holed plants ÷ 100
Example - 25 shot-holed plants and 1.5 larvae per unfurled plant
larvae per plant 0.38 = 1.5 x 25 ÷ 100
A yield loss of 5% per live larvae is estimated.1 Therefore:
C. Potential % yield loss ___________ = (B) x 5 ÷ 100
D. Potential $ loss ___________ = (C) potential % yield
loss x expected yield t/ha (bu/acre) x value $/t ($/bu)
A 75% effectiveness of a pesticide treatment is estimated.1
Therefore:
E. $ preventable loss ___________ = (D) potential $ loss x %
effectiveness of pesticide treatment
F. Treatment cost ___________ = pesticide cost + application
cost
G. Gain (+) or loss (-) if treatment is applied ___________
= (E) - (F)
1 Use another estimated value if desired.
Bivoltine Strain (for areas where there are
two generations of ECB per year)
A. Larvae per plant ___________ = number of egg masses/plant
x 2 borer / egg mass1
(cumulative counts taken 7 days apart)
B. % yield loss ___________ = (A) larvae / plant x 4%
yield loss per larvae/plant2
C. Yield losst/ha (bu/acre) ___________ = % yield loss
x expected yield t/ha (bu/acre)
D. $ loss/ha (acre) ___________ = (C) yield loss t/ha
(or bu/acre) x expected $ price per bu
E. Preventable loss per ha (acre) ___________ = (D)
$ loss per ha (or acre) x 75% control3
F. Treatment cost ___________ = pesticide cost + application
cost
G. Gain (+) or loss (-) if treatment is applied ___________
= (E) - (F)
1 Assumes a survival rate of 2 larvae per egg mass. This may
vary with weather and egg mass size.
2 Use a 3% loss per borer per plant if infestation occurs after
silks are brown. The economic benefit of treatment declines rapidly if infestations
occur after the blister stage.
3 75% is an average. Use another estimated value if desired.
