Abstract
Homemade botanical insecticides are widely used by subsistence and transitional farmers in low-income countries. Their use is often driven by the limited availability or cost of commercial pesticides. Homemade botanical insecticides are often recommended by agricultural extension services and some development organizations. However, this could be questioned because scientific evidence of their efficacy and safety may not be available or accessible. Although botanicals with insecticidal properties have been widely studied, a synthesis focusing specifically on homemade preparations used in realistic field or storage conditions is missing. In this paper, we review efficacy assessments of botanicals used to prepare homemade insecticides. This covers twelve botanicals recommended by national extension partners in 20 countries within the global agricultural Plantwise program. These are as follows: garlic (Allium sativum), neem (Azadirachta indica), chili pepper (Capsicum spp.), Siam weed (Chromolaena odorata), mother of cocoa (Gliricidia sepium), chinaberry (Melia azedarach), moringa (Moringa oleifera), tobacco (Nicotiana tabacum), clove basil (Ocimum gratissimum), tephrosia (Tephrosia vogelii), tree marigold (Tithonia diversifolia), and bitter leaf (Vernonia amygdalina). This review shows that (1) all the selected botanicals contain active ingredients with insecticidal, antifeedant, or repellent properties, and (2) homemade insecticides based on all the selected botanicals have been used with some success to control pests or prevent damage, although efficacy was variable and often lower than the positive controls (synthetic pesticides). Factors affecting the efficacy of homemade botanical insecticide include variation in active ingredient content and concentration in plant material, as well as variation in the preparation process. In conclusion, there is some evidence that homemade botanical insecticides could contribute to reducing losses in food production. Since further research is needed to better understand their variable efficacy and potential health and environmental risks, those who promote the use of homemade botanical insecticides should also communicate those “unknowns” to the farmers who use such products.
Highlights
Yield losses due to arthropods, diseases, and weeds are estimated to account for about 35% in major crops
Our review shows that active ingredients with insecticidal properties have been isolated in all the botanicals covered by this study
The data indicate that homemade insecticides based on the 12 selected botanicals have the potential to lower arthropod pest populations or to reduce the losses they cause
Summary
Yield losses due to arthropods, diseases, and weeds are estimated to account for about 35% in major crops. Many subsistence and transitional farmers do not have access to synthetic pesticides, or cannot afford them (Abate et al 2000; Nyirenda et al 2011). Up to 100% of the farmers in some regions of Zimbabwe and Uganda report using botanicals or have used them (Makaza and Mabhegedhe 2016; Nyirenda et al 2011) These typically involve simple preparations, such as ground or whole plant material, and aqueous extracts thereof (Fig. 1). National extension partners in Plantwise (www.plantwise.org), a global agricultural development program led by CABI (Centre for Agriculture and Bioscience International), sometimes include homemade pesticide preparations in their recommendations and extension materials. As well as practical and economic aspects, are briefly discussed
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