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Scouting for European Corn Borer
A recommended scouting procedure for corn borer monitoring is:
For a 40 acre field, pull the whorls from 10 plants at five locations across the field. Count the number of larvae inside the whorl (a more accurate method than only counting shotholed plants). Select plants at random, not just because a plant is thought to have larvae (e.g. shotholed leaves). Begin collecting samples at least 100 feet in from the edge of the field. Space the sample sites across the entire field. Record the number of larvae found per infested plant. This will allow you to determine average number of larvae per infested plant. Adjust the number of sampling sites within a field upward for larger fields. Use the following worksheets to help determine the economic benefit from a possible treatment
Worksheet for whorl stage corn -- fill in the blanks
1. __ %plants infested x __ Avg borers/plnt = __ Borers/plant
2. __ borers/plant x __ %loss/borer* = __ % yield loss
3. __ % yield loss x __ expected bu/a = __ bu/a loss
4. __ bu/a loss x __ price/bushel =$__ loss/acre
5. __ loss/acre x __ % control** =$__ prevent loss/a
6. __ prevent loss/a - __ control cost/a =$__ profit (loss)/a
*5% for corn in early whorl stage; 4% for late whorl; 6% for pre-tassel.
**80% for granules; 70% for sprays.
Worksheet for tassel stage or older corn -- fill in the blanks
1. __ egg masses/plnt* x 4.5 borer/egg mass = __ borers/plant
2. __ borers/plant x __ % loss/borer** = __ % yield loss
3. __ % yield loss x __ expected bu/a = __ bu/a loss
4. __ bu/a loss x __ price/bushel =$__ loss/acre
5. __ loss/acre x 80 % control =$__ prevent loss/a
6. __ prevent loss/a - __ control cost/a =$__ profit (loss)/a
*Cumulative counts taken five to seven days later can be added here.
**Use 0.04 for pollen-shedding corn, 0.03 if kernels are initiated.
Insecticides currently registered and recommended for corn borer control in North Dakota are:
For more information see the Insect Guide at http://www.ext.nodak.edu/extpubs/plantsci/pests/e1143w1.htm
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