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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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.

 

 


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Author: OMAFRA Staff
Creation Date: 20 May 2009
Last Reviewed: 20 May 2009