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Whitefly-transmitted viruses are a growing threat to modern day agriculture. Their impact on South Africa's vegetable industry results in unprecedented economic losses. Tomatoes are important vegetable crops that are highly susceptible to whiteflies and an almost indispensable part of meal preparation in many South African homes. Against this background, tomato crops and nearby weed species in South Africa were surveyed for whitefly-transmitted viruses. In addition, some pepper crops in adjacent tomato fields were also included in this study. Field and greenhouse crops were inspected for the development of virus-like symptoms in the presence of whitefly infestations. Leaf samples exhibiting virus-like symptoms were collected and analyzed for whitefly-transmitted crini-, torrado-, begomo-, ipomo- and carla viruses using molecular assays. The identity of each virus positive sample was confirmed by Sanger sequencing and used in subsequent phylogenetic studies. Tomato chlorosis crinivirus (ToCV), Tomato torrado virus (ToTV) and Tomato curly stunt begomovirus (ToCSV) were three major viruses identified in the study. ToCV was the most abundant whitefly-transmitted virus in South Africa with an overall prevalence of 47.1% (tomatoes) and 21% (weeds). ToCV isolates from South Africa matched ≥97% to isolates from Spain and Sudan. ToTV outbreaks emerged on tomato crops in the northern parts of South Africa in the presence of abnormally high whitefly populations. ToTV infections of tomatoes were restricted to the Limpopo province, however, a second isolate was identified on an unknown arable weed that did not infect nearby tomato crops. ToTV isolates from South Africa matched 99% and 92.8% to Polish and Italian isolates and had an overall incidence of 7.5% (tomatoes) and 11% (weeds). ToCSV isolates from South Africa matched 100% with Mozambican isolates. Phylogenetic analysis showed that current ToCSV isolates in South Africa were distantly related to a previously identified South African ToCSV isolate. The disease was identified on tomatoes in three provinces and had an overall incidence of 9.4%. On the contrary, whitefly-transmitted viruses were not identified on pepper crops exhibiting virus-like symptoms. In this study, whitefly-transmitted viruses infecting tomatoes, and some weed species in South Africa were elucidated. These findings are intended to raise awareness on the impact of whitefly-transmitted viruses in South Africa's tomato industry. • A national survey of whitefly-transmitted viruses infecting tomato crops. • Prevalence and epidemiology of whitefly-transmitted viruses in South Africa. • Three major virus species identified i.e. ToCV, ToTV, and ToCSV. • Weeds influence virus epidemiology. [ABSTRACT FROM AUTHOR]

Provision of permanent soil cover using crop residues in conservation agriculture (CA) is constrained by livestock grazing and termite consumption in smallholder farming systems of sub Saharan Africa. This study evaluated the effects of surface applied maize ( Zea mays L.) crop residues on termite prevalence, crop damage due to termite attack and maize yield over two seasons, 2008/9 and 2009/10. Treatments with residue application rates of 0, 2, 4 and 6 t ha −1 under CA and a conventional mouldboard ploughing (CMP) control were laid out in a randomized complete block design with four replicates on three farm sites in Kadoma, Zimbabwe. Maize residues increased (P < 0.05) termite numbers compared to CMP treatment. Crop lodging at harvest increased (P < 0.05) from 30 to 34% in CMP to 42–48% in CA systems. However, no significant difference was found in crop lodging with increasing residue rates within CA treatments. Significantly higher crop yields were observed under CA (P < 0.05) ranging from 2900 - 3348 kg ha −1 in 2008/9 season compared to CMP with 2117 kg ha −1 . Nevertheless, increasing residue cover in CA did not necessarily increase maize crop yield. Thus, increasing crop residue application rates under CA increased termite prevalence while crop lodging was influenced more by soil tillage system than by crop residue application rates. [ABSTRACT FROM AUTHOR]

Conservation agriculture (CA) is increasingly promoted in southern Africa as a strategy to improve food security and reverse soil degradation in the face of climate change. However, the performance of CA under different environments and its ability to improve ecosystem services is still unclear. The effects of the CA options; direct seeding, rip-line seeding, and seeding into planting basins on maize grain yield, soil health and profitability across agro-ecological regions in Zimbabwe were evaluated through a review of literature in combination with meta-analysis. Overall, CA improved maize yield over conventional agriculture. Compared to conventional agriculture, direct seeding, rip-line seeding, and seeding into planting basins increased yield by 445, 258 and 241 kg ha −1 , respectively. However, there was an initial yield decline in the first two years. CA practices reduced soil erosion and bulk density, and increased soil water content in most studies. Under high levels of residue retention (6 Mg ha −1 ), CA systems exhibited greater macro fauna abundance and diversity than conventional agriculture, particularly termites. Weed pressure tended to increase labour requirement for hand-hoe weeding under CA compared to conventional agriculture. However, the use of herbicides reduced weeding labour demand during the early season. The benefits of CA are tied to the farmers’ management intensity including: time of planting, weeding, fertiliser and herbicide application, and adequate training on equipment use. Economic analysis results showed that on average, a farmer incurs losses for switching from conventional agriculture to CA in the main maize growing regions of Zimbabwe. Based on the six seasons’ data, the losses were least with the ripper in drier areas and worst with the direct seeder in wetter areas. Incorporation of chemical herbicides worsens the economic returns of CA tillage options in all the agro-ecological zones. Overall, the study showed that the rip-line seeding is more attractive in the drier areas than direct seeding. Although not costed in this study, critical is the cumulative reversal of soil degradation associated with consistent CA practice which can sustain agriculture. Results from this review suggest that the benefits of CA depend largely on the type and context of CA being practised. It is thus imperative to profile the technology, the farmer socio-economic circumstances and the bio-physical environment in which the farmer operates for proper geographical and beneficiary targeting to achieve greater impact. More longer-term studies are required to fully elucidate the benefits and context of CA options and practice. [ABSTRACT FROM AUTHOR]

Abstract: The study was carried out to evaluate the impact of tillage system in combination with different herbicides on weed density, diversity, crop growth and yields on 18 farms in Kadoma, Zimbabwe. Experiments were set up as a split plot design with three replications on each farm. Tillage was the main plot (Conservation Tillage (CT), Conventional Tillage (CONV)) and weeding option (hand weeding, cyanazine, atrazine, glyphosate only and mixture of cyanazine + alachlor and atrazine + alachlor) as the sub-plots. Due to the heterogeneous nature of farmers' resource base, the farms were grouped into three farm types: high (Type 1), medium (Type 2) and poorly resourced farmers (Type 3). The hand hoe weeded treatments had 49 percent higher total weed densities in CT relative to CONV, and was statistically similar to the glyphosate treatment. The mixed pre-emergence herbicides reduced the diversity indices by 69 and 70 percent when compared to the hand hoe weeded treatment under CT in cotton and maize, respectively. The effectiveness of all pre-emergence herbicides were not influenced by tillage but were affected by farmers resource endowments with pronounced effect in Farm Type 1. Maximum plant heights of 85 and 238 cm were recorded for mixed pre-emergence herbicides under CT for cotton and maize, respectively. Minimum plant heights of 75 and 217 cm were recorded for the respective hand hoe weeded treatments. The hand hoe weeded treatments resulted in average cotton lint yield of 1497 and 2018 kg ha−1 for maize. The mixed pre-emergence herbicides treatments gave yields of 2138 and 2356 kg ha−1 of cotton and maize, respectively. The higher weed densities in CT under hand weeded treatments underscored the need for other weeding options. Similarly, a mixture of cyanazine + alachlor in cotton and atrazine + alachlor in maize is recommended for suppressing broad and grass weed populations and enhancing yields in CT systems. [Copyright &y& Elsevier]

Abstract: Rotation of nitrogen-fixing woody legumes with maize has been widely promoted to reduce the loss of soil organic matter and decline in soil biological fertility in maize cropping systems in Africa. The objective of this study was to determine the effect of maize-fallow rotations with pure stands, two-species legume mixtures and mixed vegetation fallows on the richness and abundance of soil macrofauna and mineral nitrogen (N) dynamics. Pure stands of sesbania (Sesbania sesban), pigeon pea (Cajanus cajan), tephrosia (Tephrosia vogelii), 1:1 mixtures of sesbania+pigeon pea and sesbania+tephrosia, and a mixed vegetation fallow were compared with a continuously cropped monoculture maize receiving the recommended fertilizer rate, which was used as the control. The legume mixtures did not differ from the respective pure stands in leaf, litter and recycled biomass, soil Ca, Mg and K. Sesbania+pigeon pea mixtures consistently increased richness in soil macrofauna, and abundance of earthworms and millipedes compared with the maize monoculture (control). The nitrate-N, ammonium-N and total mineral N concentration of the till layer soil (upper 20cm) of pure stands and mixed-species legume plots were comparable with the control plots. Sesbania+pigeon pea mixtures also gave higher maize grain yield compared with the pure stands of legume species and mixed vegetation fallows. It is concluded that maize-legume rotations increase soil macrofaunal richness and abundance compared with continuously cropped maize, and that further research is needed to better understand the interaction effect of macrofauna and mixtures of organic resources from legumes on soil microbial communities and nutrient fluxes in such agro-ecosystems. [Copyright &y& Elsevier]

Abstract: The use of participatory research methods in evaluating tree legumes has received little attention among researchers because of the widely-held assumption that data generated in this way are qualitative and not amenable to statistical testing. Using a participatory tool called a bao game, 112 farmers in eastern Zambia rated 11 agroforestry trees for soil fertility improvement, source of fuel wood, light construction materials, poles and fodder. Leucaena collinsii (provenance 45/85) was rated highest for provision of all the above benefits. Gliricidia sepium, Acacia angustissima and Calliandra calothyrsus (provenance ex Embu) had high scores for soil fertility improvement, while Senna siamea, Leucaena esculenta (provenance 52/87) and Leucaena pallida were rated highly for fuel wood and pole production. These later species, with the exception of Senna siamea, were also rated highly for light construction materials. A. angustissima and C. calothyrsus were rated highly for fodder production. L. diversifolia (provenance 35/88), L. diversifolia (provenance 53/88), S. spectabilis and L. esculenta (provenance ex Machakos) were rated low for all the above benefits. This work shows that the data generated using the bao game can be quantitatively analyzed in a statistically rigorous manner. [Copyright &y& Elsevier]

Although there is increasing emphasis on targeting of improved technology towards poor and female farmers, few adoption studies assess the uptake of new practices by these groups in a comprehensive manner. In this study, community members used the wealth ranking method to identify the different wealth groups in their communities, to determine each household''s wealth status, and to assess the association of wealth and different types of households with the planting of improved tree fallows, a practice for improving crop yields. There were no significant differences between the proportions of women and men planting improved fallows nor were there differences between single women and female heads of households who were married. There was some evidence of association between planting improved fallows and wealth. That 22% of the ‘poor’ group and 16% of the ‘very poor’ group were planting them suggests that there are no barriers preventing low-income households from doing so. Moreover, the proportion of females, poor, and very poor people planting improved fallows varied considerably among villages, suggesting that opportunities exist for increasing their use of the technology. Whereas the use of mineral fertilizer is strongly associated with high-income, male farmers, improved fallows appear to be a gender-neutral and wealth-neutral technology. Poor farmers appreciate improved fallows because it permits them to substitute small amounts of land and labour for cash, their most scarce resource. Finally, the high degree of consistency among different key informants in classifying households among wealth groups confirmed the effectiveness and accuracy of the wealth ranking exercise. [Copyright &y& Elsevier]