The Need for Integrated Weed Management Systems in Smallholder Conservation Farming in Zimbabwe

Abstract

This study in Zimbabwe revealed that conservation tillage systems subjected to continuous maize production to lead to unacceptably high levels of perennial weed  infestation within six years. Traditional hoe weeding proved unable to control the  rapid build-up of perennial weeds, most likely because seeds were not buried deep  enough and the observed deep tap roots and the rhizomes could not sufficiently be  lifted out of the soil. Similarly, blade weeders designed to cut through weed roots at shallow depth did not cope adequately with prolific perennials. In fact, perennials  may even have reproduced from cuttings. However, the tested blade weeders reduced weeding time considerably compared to hoe weeding and are thus well suited for controlling newly emerged annuals. Preseeding herbicide application using glyphosate at a rate of 2.2 kg ai/ha or intercropping maize with cow peas and pumkins showed greatest potential as alternative weed management options. They both suppressed perennial weeds effectively. Intercropping also had the additional benefit of increasing overall crop production thus minimizing the always present risk of total crop failure in continuous smallholder maize production. Since mixed cropping also is a traditional practice, it appears to be the most promising and appropriate weed management option for further promotion and extension in smallholder conservation farming.