Appendix G. European Corn
Borer Economic Threshold Calculations
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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.
