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Corn Insect Thresholds |
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Growth Stage
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| Pest | Preplant | Emergence to 4 leaf stage | 5 leaf stage to silking |
| White Grubs | 1 per sq. ft. - sandy soils
2 per sq. ft. - clay soils |
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| Wireworms | 1 per sq. ft. - sandy soils
2 per sq. ft. - clay soils |
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| Slugs | 3 per sq. ft. | 3-5 per plant | |
| Cutworms |
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1-2 leaf - 3% cut or 10% feeding damage
2-4 leaf - 5% cut and larvae present |
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| Corn flea beetle | 5-6 per plant and 50% plants damaged | ||
| Common stalk borer |
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2 leaf - 4% infested plants
3 leaf - 6% infested plants 4 leaf - 10% infested plants |
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| European corn borer |
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50% plants infested (irrigated)
80% plants infested (non-irrigated) |
50% plants infested (irrigated)
80% plants infested (non-irrigated) |
| True armyworm | 25% plants infested and larvae < 1" | 25% plants infested and larvae < 1" | |
| Cereal leaf beetle | 10 per plant and 50% plants damaged | ||
| Fall armyworm |
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75% plants infested with 1 worm or 50% plants with 2 or more worms |
| Northern corn rootworm * | 2 adult beetles per plant | ||
| Western corn rootworm * | 1 adult beetle per plant | ||
* if both present - divide number of northern corn rootworms by two and add to number of western corn rootworms