Interaction between herbicides, time of application and genotype of wild oats (Avena fatua L.)

Abstract

A glasshouse experiment was conducted on three groups of genotypes of Avena fatua L. representing those from the north, central and southern regions of the temperate area of Western Australia with a winter growing season. The interaction between genotype groups, three herbicides (barban, difenzoquat and flamprop-methyl) and six times of application was investigated. The results showed that all genotypes did not react similarly to the herbicides tested. Barban, in particular, was very susceptible to the genotype x time of application interaction. Reasons for this are suggested. These include the effect of climatic parameters on the evolution of predominant genotypes in various areas, together with micromorphological variability developed in response to environmental pressure. It is also suggested that the number of days after seedling emergence is as reliable a guide as leaf number for optimum application of barban and that mature wild oat seed-head counts may not adequately reflect important competitive attributes such as dry matter production. The possible erroneous extrapolation to subspecies level from data collected on a species basis is emphasized, as is the possibility of differentially specific herbicides contributing to population shifts towards greater herbicide resistance, and not only in wild oats. Lines of future research are indicated.