Effect of herbicide application on weed flora under conservation agriculture in Zimbabwe

abstract Increased challenges of weed control in the smallholder farming sector of southern Africa have oftenresulted in small yields. The objective of this study was to evaluate the effects of different weed controlstrategies onweed flora and composition under conservation agriculture (CA) systems in Zimbabwe. Thisstudy was conducted at three on-station trial sites namely Domboshawa Training Centre (DTC), Uni-versity of Zimbabwe farm (UZ farm) and Henderson Research Station (HRS) in a maizeesoybean rotationfor four seasons from 2009e2010 to 2012e2013 seasons. Hand weeding was done whenever weeds were10 cm tall or 10 cm in circumference for weeds with a stoloniferous growth habit. Weed identificationwas done up to the weed species level, and the ShannoneWeiner diversity and evenness index was usedto determine the response of weed flora to herbicides. Results showed that there were more weeds in theearly years which decreased gradually until the final season. Weed species diversity was not affected byherbicide application and the results indicated that weed species diversity was small in CA systems.Annual weed species constituted a greater proportion of species, and species richness decreased with theduration of the study. Richardia scabra L. and Galinsoga parviflora Cav. were the most common dominantweed species at all sites and in all seasons. Moreover, herbicide application had no effect on the evennessof weeds in the plots but site characteristics had a significant effect on the distribution of weed species(weed species evenness). The results presented in this study suggest that herbicide application facilitatesa depletion of weed seed bank/number of weeds over time. Thus, herbicide application in CA has po-tential to reduce weed density, species richness and species diversity in the long term which may lead tomore labour savings and larger yields.© 2014 Elsevier Ltd. All rights reserved.