Abstract
Manual weeding, maize-cowpea intercropping, pre-emergence (PRE) and early post-emergence (EPOST) herbicide applications comprised ten weed control practices evaluated in the 2015-16 cropping season on weed species structure and maize (Zea mays L.) yield in the Middleveld and Highveld of Swaziland. The herbicides used were Harness (acetochlor) and Dual Gold (S-metolachlor) as pre-emergence applications and Micro-Tech (alachlor) and Callisto (mesotrione) as early post-emergence applications. PRE and EPOST herbicides were used as once-off or combined applications besides manual weeding or intercropping practices. Results indicated that the combination of PRE and EPOST herbicides reduced both species richness (number) and evenness (dominance) but weed species composition (types) were not distinguished amongst treatments. Manual weeding in combination with PRE herbicides or maize-cowpea intercropping resulted in significantly lower weed density and biomass as compared to singular or combinations of PRE or EPOST herbicides in both locations. The effects of weed control practices on grain yield of maize were not significantly distinguished among weed control practices between the two sites. The study reaffirmed that herbicides may need to be supplemented with other weed control strategies to obtain acceptable weed control. Key words: Herbicides, maize, Shannon-Wiener diversity index, Simpson’s dominance index, Steinhaus coefficient index, weeds.
Highlights
Despite benefits that have been reported from chemical weed control practices in small scale crop production, effective control of weeds remains a major impediment to productivity as weed infestations continue to cause debilitating effects on crop health and human welfare under subsistence production (Gianessi and Williams, 2011)
The highest kernel yield (4348.9 kg ha-1) obtained with maize-cowpea + manual weeding at Mangcongco was not significantly different from yields obtained with other weed control practices
The highest kernel yield (4348.9 kg ha-1) obtained with maize-cowpea intercropping + manual weeding at Mangcongco was not significantly different from yields obtained with other weed control practices
Summary
Despite benefits that have been reported from chemical weed control practices in small scale crop production, effective control of weeds remains a major impediment to productivity as weed infestations continue to cause debilitating effects on crop health and human welfare under subsistence production (Gianessi and Williams, 2011). Most herbicide applications are limited to post-emergence (Mncube et al, 2017) and farmers do not practice soil cultivation practices to reduce weed escapes. Sustainable agriculture calls for limiting use of herbicides either by reducing application rates (Zhang et al, 2013), herbicide rotations, use of selective narrowspectrum products, containing the most ecologically detrimental range of products (Norsworthy et al, 2012) or using alternative soil and crop management methods (Pacanoski et al, 2015; Saudy, 2015). Development of effective strategic combinations of weed control techniques, where herbicides are a part, remains a major limitation to farmers and their agents in emerging agriculture already beset with poor adoption of herbicide technology
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