Evaluation of the Atrazine-Fallow Technique for Weed Control and Seedling Establishment

Abstract

The atrazine-fallow technique was evaluated for 3 years on study areas of from 50 to 1,000 acres. Atrazine at 0.6 to 1.2 lb/acre was applied in the fall by ground rig, by fixed-wing aircraft, or by helicopter. Ground-rig application gave the most uniform control of cheatgrass and tumble mustard during the fallow year. Air application usually left weedy strips between swaths of excellent weed control. Wheatgrasses and other species of grasses and forbs were fall-seeded with the standard and deep-furrow rangeland drills 1 year after herbicide application. Fair to excellent seedling stands were obtained in all years. However, in 1 year a valid evaluation of treatment effects was not possible because of depradation and unusually high spring precipitation in the seedling year. In 2 years, environmental conditions were near normal, and depredation was reduced by use of large study areas and insect control. Under these conditions, good established stands of crested, intermediate, pubescent, and Siberian wheatgrasses were obtained by the chemical-fallow technique.