Calculations for Univoltine Threshold
(if profitable to treat a field )

Plants with shotholes_____/total plants checked____= ______(A)

Unfurl one of the shotholed plants from each location and look for live larvae

Multiply the average number of live larvae/unfurled plant ____ times (A) ____from above, which gives you live larvae/plant___(B).

(Example: 25 shotholed plants/100 plants = .25 =(A).If there are an average of 1.5 live larvae/unfurled plant, 1.5 x .25 = .38 = (B))

We figure there is about 5% yield loss/live larvae. Therefore, (B) from above times 5% is equal to your potential, percent yield loss _____(C).

Multiply ____(C) times your expected yield _____t/ha (or bu/ac) times value/tonne (or bu) = $____ (D). This is your loss potential in dollars.

Multiply _____(D) times expected effectiveness of a pesticide treatment (suggest 75%) and you arrive at the preventable loss in dollars/ha (or ac) $_______.

Compare your preventable loss to the cost of application plus pesticide and you will see if the treatment is cost effective.

Calculations for Bivoltine Threshold
(if profitable to treat a field )

________ number of egg masses/plant x 2borer/egg mass* = borers/plant (cumulative counts, taken 7 days apart)

________borers/plant x ____4 ___ % loss/borer** = ________ % yield loss

________% yield loss x _______ expected yield = _________ t/ha (or bu/ac) loss

________t/ha (or bu/ac) loss x $________ price/bu = $___________ loss/hectare (or acre)

$_____loss/hectare (acre) x ___75___% ***control = $_____ preventable loss/hectare (or acre)

$_____preventable loss/hectare (acre) - $_____ cost of control/hectare (or acre) =___________

$_______gain (+) or loss (-) per acre if treatment is applied

*Assumes survival rates of two borers per egg mass; may vary with weather and egg mass size.

** Use 3% loss per borer per plant if infestation occurs after silks are brown. The potential economic benefits of treatments decline rapidly if infestations occur after the corn reaches the blister stage.

*** 75% is an average, use another value if desired.