IPM – Corn Insect Thresholds

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Growth Stage
Pest Preplant Emergence to 4 leaf stage 5 leaf stage to silking
White Grubs 1 per sq. ft.
Wireworms 1 per sq. ft.
Slugs 3 per sq. ft. 3-5 per plant
Cutworms 1-2 leaf – 3% cut or 10% feeding damage 2-4 leaf – 5% cut and larvae present
Corn flea beetle 5-6 per plant and 50% plants damaged
Common stalk borer 2 leaf – 4% infested plants 3 leaf – 6% infested plants

4 leaf – 10% infested plants

European corn borer 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 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