Evaluation of pesticidal plants for smallholder grain protection

Widespread and indiscriminate use of synthetic pesticides for storage pest control can cause serious problems including: pest resistance build-up, pest resurgence, environmental and health concerns. Pesticidal plants can be an effective alternative for resource-poor farmers because of their local availability, ease of use and minimal cost. Knowledge of application methods, safety and efficacy of these pesticidal plants based on scientific evidence is scanty even though farmers are already using the materials. The insecticidal properties of different pesticidal plants used as grain protectants by smallholder farmers in Zimbabwe were evaluated against maize, cowpeas and beans storage insect pests to validate, improve and optimize the efficacy of the plants. In a series of experiments, eight local plants already being used by smallholder farmers were tested separately as leaf, fruit or bark powders or ashes admixed with grain and compared with a commercial pesticide or an untreated control. Application rates ranged from 2-5% w/w on-station or on-farm while in laboratory bioassays 2-10% w/w were used. The plants tested included Dirostachys cinerea, Bobgunnia (Swartzia) madagascariensis, Bauhinia thoningii, Lippia javanica, Aloe spp., Spirostachys africana, Combretum imberbe and Maerua edulis. Based on % insect damaged grain and insect mortalities; B. madascariensis, L. javanica, Aloe spp. and Maerua edulis showed potential. The bruchids, Callosobruchus rhodesianus and Acanthosclides obtectus, were particularly susceptible while the bostrychids, Prostephanus truncates and Rhyzopertha dominica, were less susceptible. Most of the plant materials were not persistent on grain and were not effective for more than 16 weeks whereas smallholder farmers normally store for about 32 weeks. This raises the need to reapply the materials mid-way the storage season. There is scope for optimising the efficacy of the plant materials and possible strategies are discussed. The results are discussed in the context of effective and sustainable use of the pesticidal plants by resource-poor farmers

Evaluation of pesticidal plants for smallholder grain protection

Widespread and indiscriminate use of synthetic pesticides for storage pest control can cause serious problems including: pest resistance build-up, pest resurgence, environmental and health concerns. Pesticidal plants can be an effective alternative for resource-poor farmers because of their local availability, ease of use and minimal cost. Knowledge of application methods, safety and efficacy of these pesticidal plants based on scientific evidence is scanty even though farmers are already using the materials. The insecticidal properties of different pesticidal plants used as grain protectants by smallholder farmers in Zimbabwe were evaluated against maize, cowpeas and beans storage insect pests to validate, improve and optimize the efficacy of the plants. In a series of experiments, eight local plants already being used by smallholder farmers were tested separately as leaf, fruit or bark powders or ashes admixed with grain and compared with a commercial pesticide or an untreated control. Application rates ranged from 2-5% w/w on-station or on-farm while in laboratory bioassays 2-10% w/w were used. The plants tested included Dirostachys cinerea, Bobgunnia (Swartzia) madagascariensis, Bauhinia thoningii, Lippia javanica, Aloe spp., Spirostachys africana, Combretum imberbe and Maerua edulis. Based on % insect damaged grain and insect mortalities; B. madascariensis, L. javanica, Aloe spp. and Maerua edulis showed potential. The bruchids, Callosobruchus rhodesianus and Acanthosclides obtectus, were particularly susceptible while the bostrychids, Prostephanus truncates and Rhyzopertha dominica, were less susceptible. Most of the plant materials were not persistent on grain and were not effective for more than 16 weeks whereas smallholder farmers normally store for about 32 weeks. This raises the need to reapply the materials mid-way the storage season. There is scope for optimising the efficacy of the plant materials and possible strategies are discussed. The results are discussed in the context of effective and sustainable use of the pesticidal plants by resource-poor farmers

Effects of crop residues and reduced tillage on macrofauna abundance

Abstract Conservation agriculture is promoted to safeguard resilient properties of soils and to reclaim degraded arable lands. This is achieved through creating necessary conditions for fauna recolonisation. A study was carried out at Kadoma and Southeast Lowveld of Zimbabwe to assess the effects of conservation agriculture practices on soil macrofauna diversity in the 2008-2009 agricultural season. A randomized complete block design experiment, where four crop residue levels (0t/ha, 2t/ha, 4t/ha and 6t/ha) were replicated four times on un-tilled plots at five sites, was used. Soil fauna found in collected monoliths were identified and quantified. Analysis of variance showed significance (P<0.001) in site and treatment effects on both macrofauna abundance and diversity. Reduced tillage with residue cover yielded significantly (P<0.05) higher species richness and macrofauna abundance than conventional systems. There was a significant correlation (r 2 =0.767) between residue amount and species richness. Although there was no apparent consistent relationship between treatment and species richness, diversity and evenness; abundance was in the order 6t/ha>4t/ha>2t/ha>0t/ha>Conventional systems. The major macrofauna groups observed were termites, ants and beetle-larvae. It was concluded that short-term conservation agriculture systems has significantly positive effects on macrofauna species richness and abundance, which are crucial for initiating soil regeneration. The results are discussed in the context of sustainable crop production using conservation agriculture by resource poor farmers

Pesticidal effects of indigenous plant extracts against rape aphids and tomato red spider mites

Aphids, Brevicoryne brassicae and Red spider mites, Tetranychus evansi are the most damaging pests of rape, Brassica napus and tomato, Solanum lycopersicum, respectively. Farmers respond by using synthetic pesticides which pose environmental challenges. Extracts of Lippia javanica leaf powder and Solanum delagoense ripe fruit pulp were evaluated for pesticidal effects under on-station conditions against rape aphids and tomato red spider mites as alternatives to conventional pesticides and in comparison to Neem, Azadirachta indica leaf powder. The extracts of A. indica, L. javanica and S. delagoense were mixed with water at 8, 12.5 and 25 % w/v respectively. Amitraz and dimethoate were applied on tomato and rape respectively at label rate. Extracts were kept for 24 h at room temperature and then sieved. A liquid soap surfactant was added at 0.1 % v/v, prior to spraying. Sprays were applied weekly once pest infestations had established within the crop. Pests were counted 24 h after spraying for six weeks. Plant extracts significantly reduced pest numbers (P < 0.05) in both experiments. Dimethoate reduced aphid by 96 % while amitraz reduced red spider mite by 72%. L. javanica and S. delagoense at 12.5 and 25 % reduced aphids by 63 % and 57.9 % and mites by 66.5 % and 55 %, respectively. Both extracts were more effective on aphids than mites while L .javanica was more effective than S. delagoense on both crop pests. L. javanica and S. delagoense had some pesticidal effects against the vegetable pests

Botanical pesticide production, trade and regulatory mechanisms in sub-Saharan Africa: making a case for plant-based pesticidal products

Pesticides are the major technology used in the management of field and postharvest losses due to pests. There is growing demand for effective alternatives that present low health risks and conserve ecosystems and biological diversity. Pesticidal plants are increasingly used as alternatives where synthetic products are unaffordable, have limited availability or are ineffective. Plant materials, however, are often used inefficiently and their effective use requires optimisation. In Africa wide-scale uptake of pesticidal plants remains limited despite the success of pyrethrum in some countries and other pesticidal plant products in China and India. This is mainly due to lack of data on efficacy and safety, inconsistent efficacy of plant products, the prohibitive cost of registration, and an inadequately developed conventional pesticides sector. Globally, the demand for botanicals is poised to grow due to an increasing shift in consumer demand for safe food, increasing organic farming, lobbying by environmentalists and the increasing pressure from new regulations on internationally traded foods in Europe. These demands can only be met by formalising production, marketing and use of pesticidal plants. This has to be supported by friendly registration procedures, sustainable forest management, propagation and cultivation of pesticidal plants. This paper presents a critical review of the enabling environment required for wide-scale adoption and commercialisation of botanical pesticides in sub-Saharan Africa. We conclude that regulations and protocols for production, marketing and trade need to be reviewed to facilitate the development of the botanicals sector in Africa