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 preemergence 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.

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The effects of okra [Abelmoschus esculentus (L.) Moench], soybean (Glycine max L.) and maize (Zea mays L.) on weed growth were examined in a field experiment carried out at Luyengo (26°34'S; 31°12'E) in the Middleveld of Swaziland. The aim was to check consistency of competitiveness of crops under different weed removal regimes. Two series of weed removal treatments were included. In the first series, treatments of increasing duration of weed control were maintained weedfree until 3, 7 or 11 weeks after emergence of the crops. The weeds were subsequently allowed to develop till crop harvest. In the second series, weeds were allowed to develop with the crops from emergence until 3, 7 or 11 weeks after crop emergence; then the plots were kept weed-free till harvest. The weed species Oxalis latifolia, Cyperus esculentus, Amaranthus hybridus, Ipomoea purpurea and Nicandra physaloides occurred throughout the different weed-infested and weed-free interference durations. Commelina benghalensis and Acanthospermum hispidum were particularly predominant under increasing weed infestation treatments. The similarity matrix based on Jaccard's coefficient showed that the composition of weeds under weedfree treatments in soybean was not identical to that of maize and okra, respectively. Further, the weed flora was not homogenous under different lengths of weed-free period showing the combined influence of weed removal and crop on the composition of weed infestation. There were no significant differences in the prevalence of weeds with either C 3 or C 4 photosynthetic pathways associated with the three crops. A longer equality point of weed control and interference, and lower regression coefficient between weed biomass and yield for soybean compared to maize and okra suggested decreased sensitivity of soybean to weed interference. The results indicate potential for competitive crop genotypes such as soybean for use in intentionally designed cropping systems to augment weed control practices.