TILLAGE AND WEED MANAGEMENT AFFECTS WINTER-WHEAT YIELD IN AN INTEGRATED PEST-MANAGEMENT SYSTEM

Adoption of conservation practices by U.S. Pacific Northwest growers t o meet farm bill legislation for erosion control is limited by the ina bility to control weeds and other pests in cereal and pulse crops. A 6 -yr, 16-ha integrated pest management field study was conducted in the subhumid wheat area of the Pacific Northwest from 1985 through 1991 t o develop a crop production system that controls weeds effectively and reduces soil erosion. Farm-size machinery were used to till, plant, a nd harvest crops grown in either a continuous wheat (Triticum aestivum L.) sequence or a 3-yr rotation of winter wheat-spring barley (Hordeu m vulgare L.)-spring pea (Pisum sativum L.) in conservation and conven tional tillage systems. Minimum, moderate, and maximum weed management levels were superimposed over each cropping by tillage system. Positi on of winter wheat within a cropping system influenced yield so that w heat produced more grain following spring pea > spring wheat >> winter wheat. Insects and root diseases were not yield-limiting factors in e ither conventionally tilled monoculture wheat or no-till wheat in the 3-vr cropping system. Yield of winter wheat in the conventionally till ed, continuous wheat system was similar for all three weed management levels. Yield of winter wheat in conservation tillage systems increase d at both the moderate and maximum level of weed management compared w ith the minimum level. No-till winter wheat planted after either pea o r spring wheat at the moderate and maximum weed management levels yiel ded a minimum of 605 kg ha-1 more than conventionally tilled wheat at the same management levels.