Assessing arthropod pests and disease occurrence in cassava (Manihot esculenta Crantz) and cowpea (Vigna unguiculata L. Walp) intercropping system in the Ashanti Region, Ghana

On-station trials were conducted at CSIR-Crops Research Institute’s research farms at Kwadaso and Ejura, Ashanti Region, Ghana, during 2010/2011 cropping season, to assess the pests and disease occurrence in cassava-cowpea intercrop farming systems and their effect on yield of produce. Three improved cassava varieties and a local variety were intercropped with an improved cowpea variety, and cowpea only constituted the treatments. Abundance of Bemisia tabaci was comparable between sole cassava and cassava-cowpea intercrop, but was significantly less on the sole cowpea. The incidence and severity of cassava mosaic disease was higher on the local variety than on the improved varieties. Root yield of cassava did not differ between sole and intercropped cassava with cowpea. However, Kwadaso had higher root yield than Ejura. Dry grain yield of cowpea was similar at Kwadaso and Ejura for both sole and intercrop scenarios. This baseline information will be useful on disease and pests incidence in sole crop and cassava-cowpea intercropping system

Insecticidal activity of a native Australian tobacco, Nicotiana megalosiphon Van Heurck & Muell. Arg. (Solanales: Solanaceae) against key insect pests of brassicas

Concerns over the harmful effects of synthetic insecticides have stimulated interest in alternative pest management tactics including botanical insecticides that provide novel modes of action against pests that have developed resistance against synthetic insecticides. Much work has been conducted using plants native to various developing countries but the Australian flora has been little explored as a source of novel plant protection treatments. Here we report potent insecticidal properties of the Australian plant, native tobacco Nicotiana megalosiphon against three key pests of brassicas: the diamondback moth (Plutella xylostella), cabbage aphid (Brevicoryne brassicae) and the green peach aphid (Myzus persicae). Aqueous extracts (1%, 5% and 10% w/v) of N. megalosiphon gave up to 100% control of P. xylostella; better than the recommended rate of tau-fluvalinate (a synthetic pyrethroid) or equivalent extracts of a second Australian native plant, Mentha satureioides. Treatment with N. megalosiphon also gave 100% control of B. brassicae at the highest two concentrations, and of M. persicae at the highest concentration. In a second study using F1 P. xylostella survivors of tau-fluvalinate treatment, the highest two rates of N. megalosiphon caused 100% mortality though efficacy of tau-fluvalinate was eroded compared with use on the previous generation. Chemical analysis of N. megalosiphon recorded the presence of anabasine at 5.2 μg/ml in water extracts of leaves and 59.4 μg/ml in methanol extracts of leaves. While these concentrations were low particularly for the water extracts they might nevertheless explain the biological activity of N. megalosiphon

Economic analysis of habitat manipulation in Brassica pest management: wild plant species suppress cabbage webworm

Chemical insecticide application has been the most widely used form of insect pest management in last six decades and resulted in well-documented negative impacts. Habitat manipulation based on intercropping to exert direct effects on pests and promote biological control has been explored in various systems as a more sustainable option. A range of intercrop plants have been evaluated, with many studies reporting successes in terms of enhanced natural enemy density, reduced pest numbers and, less commonly, reduced crop loss. Economic benefit and cost-effectiveness are less frequently explored, despite the importance of these criteria in farmer adoption and scope to scale. Here we quantify the effects of contrasting experimental habitat management treatments on densities of the pest, cabbage webworm, Hellula undalis Fab. (Lepidoptera: Crambidae), crop yield and quality, profitability and cost: benefit ratio in a cabbage Brassica oleracea var. capitata (Brassicaceae) production system in West Africa. Six wild plant species were evaluated as intercrops to promote pest suppression. Ageratum conyzoides, Tridax procumbens (Asteraceae), Crotalaria juncea (Fabaceae), Cymbopogon citratus (Poaceae), Lantana camara (Verbenaceae) and Talinum triangulare (Talinaceae) intercrop plantings were compared with a no-plant control treatment in a randomised block experiment over three growing seasons in Ghana. Costs of gathering plant propagules and establishing each intercrop plant were recorded, as was the market value of cabbage from each treatment, allowing the calculation of precise cost: benefit ratios. Hellula undalis larvae were numerous in the control compared with the intercrop plant treatments. The intercrop treatments had higher undamaged yields compared with the control. Reflecting this, and establishment costs, intercrop plant treatments had better cost: benefit ratios than the control, ranging from 1:2.8 for C. citratus to 1:46.6 for A. conyzoides. These findings provide an important evidence base for considering the economic case for habitat manipulation control and highlight that the identity of plants used in this type of agricultural intervention has a major effect on the economic outcome

Scope for non-crop plants to promote conservation biological control of crop pests and serve as sources of botanical insecticides

Besides providing food and shelter to natural enemies of crop pests, plants used in conservation biological control interventions potentially provide additional ecosystem services including providing botanical insecticides. Here we concurrently tested the strength of these two services from six non-crop plants in managing cabbage pests in Ghana over three successive field seasons. Crop margin plantings of Ageratum conyzoides, Tridax procumbens, Crotalaria juncea, Cymbopogon citratus, Lantana camara and Talinum triangulare were compared with a bare earth control in a three-way split plot design such that the crop in each plot was sprayed with either a 10% (w/v) aqueous extract from the border plant species, a negative control (water) and a positive control (emamectin benzoate ‘Attack’ insecticide). Pests were significantly less numerous in all unsprayed treatments with non-crop plant margins and in corresponding sprayed treatments (with botanical or synthetic insecticide positive control) while treatments with bare earth margin or sprayed with water (negative controls) had the highest pest densities. Numbers of predators were significantly depressed by synthetic insecticide but higher in other treatments whether unsprayed or sprayed with botanical insecticide. We conclude that some plant species have utility in both conservation biological control and as source of botanical insecticides that are relatively benign to natural enemies. In this crop system, however, the additional cost associated with using botanical insecticides was not justified by greater levels of pest suppression than achieved from border plants alone

Tri-trophic insecticidal effects of African plants against cabbage pests

Botanical insecticides are increasingly attracting research attention as they offer novel modes of action that may provide effective control of pests that have already developed resistance to conventional insecticides. They potentially offer cost-effective pest control to smallholder farmers in developing countries if highly active extracts can be prepared simply from readily available plants. Field cage and open field experiments were conducted to evaluate the insecticidal potential of nine common Ghanaian plants: goat weed, Ageratum conyzoides (Asteraceae), Siam weed, Chromolaena odorata (Asteraceae), Cinderella weed, Synedrella nodiflora (Asteraceae), chili pepper, Capsicum frutescens (Solanaceae), tobacco, Nicotiana tabacum (Solanaceae) cassia, Cassia sophera (Leguminosae), physic nut, Jatropha curcas (Euphorbiaceae), castor oil plant, Ricinus communis (Euphorbiaceae) and basil, Ocimum gratissimum (Lamiaceae). In field cage experiments, simple detergent and water extracts of all botanical treatments gave control of cabbage aphid, Brevicoryne brassicae and diamondback moth, Plutella xylostella, equivalent to the synthetic insecticide Attack® (emamectin benzoate) and superior to water or detergent solution. In open field experiments in the major and minor rainy seasons using a sub-set of plant extracts (A. conyzoides, C. odorata, S. nodiflora, N. tabacum and R. communis), all controlled B. brassicae and P. xylostella more effectively than water control and comparably with or better than Attack®. Botanical and water control treatments were more benign to third trophic level predators than Attack®. Effects cascaded to the first trophic level with all botanical treatments giving cabbage head weights, comparable to Attack® in the minor season. In the major season, R. communis and A conyzoides treatment gave lower head yields than Attack® but the remaining botanicals were equivalent or superior to this synthetic insecticide. Simply-prepared extracts from readily-available Ghanaian plants give beneficial, tri-trophic benefits and merit further research as an inexpensive plant protection strategy for smallholder farmers in West Africa

Biopesticide based sustainable pest management for safer production of vegetable legumes and brassicas in Asia and Africa

Published online: 10 May 2019Vegetables are one of the important crops which could alleviate the poverty and malnutrition among the smallholder farmers in tropical Asia and Africa. However, a plethora of pests limit the productivity of these crops, leading to economic losses. Vegetable producers overwhelmingly rely on chemical pesticides in order to reduce pest‐caused economic losses. However, over‐reliance on chemical pesticides poses serious threats to human and environmental health. Hence, biopesticides offer a viable alternative to chemical pesticides in sustainable pest management programs. Baculoviruses such as nucleopolyhedrovirus (NPV) and granulovirus (GV) have been exploited as successful biological pesticides in agriculture, horticulture and forestry. Maruca vitrata multiple nucleocapsid NPV (MaviMNPV) was found to be a unique baculovirus specifically infecting pod borer on food legumes, and it has been successfully developed as a biopesticide in Asia and Africa. Entomopathogenic fungi also offer sustainable pest management options. Several strains of Metarhizium anisopliae and Beauveria bassiana have been tested and developed as biopesticides in Asia and Africa. This review specifically focuses on the discovery and development of entomopathogenic virus and fungi‐based biopesticides against major pests of vegetable legumes and brassicas in Asia and Africa