Effect of crop rotation, tillage practice, and herbicides on the population dynamics of wild oats in wheat

Abstract

The effects of crop rotation, tillage practice, and herbicide use on the population dynamics of wild oats (Avena fatua and A. sterilis ssp. ludoviciana) were studied in a field experiment in northern New South Wales. In the third and fourth years of a continuous wheat rotation, cultivated fallow using tines increased wild oat density and reduced grain yield compared with a no-tillage fallow. Tillage did not affect the vertical distribution of wild oat seeds in the soil, and about 80% of wild oat seeds were in the top 5 cm of soil in both tillage treatments. The seed reservoir at the end of the experiment was smaller under a no-tillage fallow regime. The half-life of wild oat seeds in the soil was about 6 months, and rotation of wheat with sorghum was the most effective means of reducing the wild oat seed reservoir. Rotational strategies for weed control are also likely to be effective in delaying or minimising the development of herbicide resistance, particularly where the average seed bank life time, as shown for wild oats in this study, is short. Annual use of either tri-allate or flamprop-methyl in 4 successive wheat crops did not prevent a massive build-up of wild oat seed. The poor performance of herbicides was partly attributed to below-average rainfall in autumn and early winter in 1985 and 1986. However, wild oats are well adapted to continuous cropping with wheat, where recruitment of 34% of the soil seed reservoir maintained the population despite the use of selective herbicides. The results of this experiment indicate that a continuous wheat rotation using herbicides to control wild oats is likely to be much less effective in reducing the wild oat seed reservoir.