EFFECTS OF CROP-ROTATION AND REDUCED CHEMICAL INPUTS ON PESTS AND PREDATORS IN MAIZE AGROECOSYSTEMS

A 2-year study examined the effects of no-rotation, 2-year and 4-year rotations with either conventional management (CM) practices (involving use of herbicides, synthetic fertilizers and prophylactic soil insecticides) or reduced chemical inputs (RCI), on insect pests and their predators in maize agroecosystems. Artificial infestations of the soil pest, southern corn rootworm, Diabrotica undecimpunctata howardi, and a foliage feeder, European com borer, Ostrinia nubilalis, were applied in order to measure the amount of predator activity. Pest populations were influenced both by rotation and by chemical-input. Multi-year rotations significantly reduced pest numbers compared with no-rotations. Reduced chemical inputs decreased pest numbers by 38% compared with CM systems. The use of herbicides and a soil insecticide reduced early-season soil predators, but their populations increased rapidly after mid-May. Predator populations were more effected by rotation, multi-year rotation systems having significantly more predators than no-rotation systems. In 1989, multi-year rotation RCI systems had significantly less com root feeding because of artificial rootworm infestations than no-rotation CM systems. Artificial European com borer infestations significantly reduced grain fill in no-rotations and CM systems compared with 2- and 4-year rotations and RCI systems.