Potential for Preseason Herbicide Application to Prevent Weed Emergence in the Subsequent Growing Season. 1. Identification and Evaluation of Possible Herbicides

Abstract

The earliest possible seeding of wheat crops in the southern Australian dryland cropping zone is prevented by the lack of a weed control practice that adequately controls initial weed seedling emergence at the start of the growing season. The objective of this study was to determine the potential for using residual herbicides applied up to 1 mo before the start of the growing season to control rigid ryegrass seedlings that emerge after the season-opening rains. In a series of glasshouse studies, S-metolachlor and propyzamide were found to effectively persist on the soil surface through prolonged exposure to hot, dry, and intense sunlight conditions, preventing the establishment of rigid ryegrass seedlings. In addition, these herbicides caused little or no effect on subsequently seeded wheat. It also was determined that S-metolachlor had the potential to retain efficacy on rigid ryegrass seedlings after 12 wk of exposure on the soil surface to these conditions. These studies have identified two herbicides with the potential for use at the novel application timing, i.e., before the commencement of the growing season, in Mediterranean climates of southern Australia.