COVER CROPS in South African Vineyards

CHAPTER 1 INTRODUCTION

Growing evidence of the drawbacks of mechanical tillage has led to greater recognition of the value of cover crops as an alternative to traditional soil- management practices.This book is a resource for growers who are interested in adopting cover crops, in that it summarises the results of long-term research trials conducted in vineyards in the main grape-growing regions of SouthAfrica.The characteristics of the trial sites are described under Regional Trial Sites in Chapter 2 (p30). An exploration of the potential of cover crops Weed suppression In recent years, chemical weed control has come under pressure as consumer opposition to agrichemical use has increased, and as more weeds have developed herbicide resistance. Cover crops offer a biological means to control weeds by preventing their germination and suppressing their growth. Besides being more environmentally friendly, biological weed control has the advantage of slowing the development of herbicide-resistant weeds. The efficacy of cover crops as weed-control agents is strongly dependent on how much biomass the cover crop produces. Firstly, the cover crop needs to grow strongly to outcompete winter-growing weeds. Secondly, the dry matter produced by the cover crop must translate into enough mulch to prevent germination of weed seeds. Biomass production by any given cover crop will depend on the climate and soil of the site where it is grown. For this reason, the long-term trials described in this book began by testing a wide range of cover-crop candidates in open-land conditions in different regions.Trials in vineyards then evaluated the most promising candidates. This work is described in Cover-Crop Selection in Chapter 3 (p46) andWeed Control in Chapter 5 (p92). Most of the cover crops discussed in this book are annuals.Throughout the book, the reader will find reference to two main management strategies for these annual cover crops in vineyard trials. In the first, the cover crops were sown every year, and full-surface chemical control was applied to the vineyard just before bud-break.As the cover crops had usually not yet flowered by this time, they did not reseed.

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