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Tuesday, 2 June 2015

Cost:benefit analysis of botanical insecticide use in cabbage: Implications for smallholder farmers in developing countries

Volume 57, March 2014, Pages 71–76

Cost:benefit analysis of botanical insecticide use in cabbage: Implications for smallholder farmers in developing countries


Highlights

Cost:benefit analysis compared botanical and conventional insecticide use.
Cost:benefit ratios ranged from 1:4 to 1: 29 for botanicals insecticides.
Ratios for conventional insecticide were 1:15 and 1:17.
For cabbage production in Africa, botanicals are an attractive option.
Equivalent studies in other crop systems are rare but should be conducted.

Abstract

Botanical insecticides based on plant extracts are not widely used as crop protectants even though they can be produced simply from locally available plants. Many studies have examined efficacy but there is a paucity of information on the cost:benefit ratio of their use compared with conventional insecticides. In the present study, crude extracts of Ageratum conyzoides (Asterales: Asteraceae), Chromolaena odorata (Asterales: Asteraceae), Synedrella nodiflora (Asterales: Asteraceae), Nicotiana tabacum (Solanales: Solanaceae), and Ricinus communis (Malpighiales: Euphorbiaceae) were compared with the synthetic insecticide, emamectin benzoate (Attack®) against insect pests of cabbage in randomised, replicated field experiments during the major and minor rainy seasons of 2012 in Ghana. The cost of each treatment including material and labour was calculated and the revenue of each derived using the value of the marketable yield of cabbage. The cost:benefit ratios of sprayed treatments were derived by comparing the cost of each plant protection regime against the additional market value of the treatment yield above that obtained in the control treatment. With the exception of plots sprayed with N. tabacum, the cost of plant protection using Attack® was higher than any of the botanicals in both seasons. The highest cost:benefit ratio of 1: 29 was observed for plots sprayed with C. odorata and was followed closely by N. tabacum treatment with 1: 25 and Attack® with 1: 18. In the minor season, plots sprayed with Attack® had the highest cost:benefit ratio of 1: 15 and was followed closely by N. tabacum with 1: 14. Botanical insecticides differed markedly in levels of pest control and cost:benefit but some were comparable to that from conventional insecticide use whilst being produced easily from locally available plant materials and are likely to be safer to use for smallholder farmers and consumers in developing countries.

Keywords

  • Biopesticide;
  • Yield;
  • Economics;
  • Ghana;
  • Africa;
  • Plutella xylostella

1. Introduction

To reduce the negative impacts of synthetic insecticides, safer alternative approaches to managing pests of vegetables must be considered by growers, especially those who do not have the expertise and equipment for safe handling and use of synthetic insecticides (Ntow et al., 2006 and Coulibaly et al., 2007). Whilst novel, less hazardous forms of insecticides such as insect growth regulators (Valentine et al., 1996) a range of non-chemical pest management techniques is available (Gurr and Kvedaras, 2010), approximately three million agricultural workers experience pesticide poisoning each year globally, and about 20,000 deaths are directly linked to agrochemical use (Dinham, 2003 and Darko and Akoto, 2008). Less than 1% of pesticides applied on crops reach the target pest, the rest can contaminate soil, water, air and food (Koul et al., 2004). In developing countries such as Ghana food commodities often contain pesticide residues, often above the maximum residue limit (Darko and Akoto, 2008 and Armah, 2011). In Ghana pesticides have been found in water, sediments, food commodities and even breast milk in areas where intensive vegetable production occurs due to injudicious use of synthetic insecticides (Ntow et al., 2006, Essumang et al., 2008 and Bempah et al., 2011).
In many developing countries, farmers are illiterate or speak and read indigenous dialects, whilst pesticides labels are printed in foreign languages (Isman, 2008). For example, even though Ghana's official language is English, it is not uncommon to find pesticides on the market that are labelled in French or Chinese (Asante and Ntow, 2009), a practice which exacerbates the inability of farmers to understand pesticides labels. This leads to unacceptable practises in handling and use of pesticides by some farmers such as tongue-testing of diluted insecticides to determine their potency (Ntow et al., 2006, Timbilla and Nyarko, 2006, Williamson et al., 2008 and Asante and Ntow, 2009).
Nearly 75% of all deaths associated with pesticidal poisoning occur in developing countries even though they use only 15% of global pesticide supply (Koul et al., 2004, Darko and Akoto, 2008 and Armah, 2011). The use of banned insecticides, applying insecticides in excess of the recommended rates due to insects resistance, using insecticides meant for industrial crops such as cocoa and cotton for vegetables, using empty pesticides containers for storing drinking water are practised in Ghana and often lead to pesticidal poisoning (Ntow et al., 2006 and Williamson et al., 2008).
Botanical insecticides based on specific compounds or crude extracts from plants with activity against insects offer a safer alternative for managing pests such as the diamondback moth (DBM), Plutella xylostella L. (Lepidoptera: Plutellidae), a key pest of crucifers which has developed resistance to most of the available synthetic insecticides ( Kianmatee and Ranamukhaarachchi, 2007, Isman, 2008, Ogendo et al., 2008 and You et al., 2013). Botanicals are also usually safer for non-target organisms, making them preferable to the synthetic insecticides ( Charleston et al., 2006).
In a survey, Gerken et al. (2001) showed that between 14% and 25% of farmers in Ghana, used traditional products for crop protection. Plants such as Azadirachta indica A. Juss. (Sapindales: Meliaceae), Cassia sophera L. (Fabales: Fabaceae), Cymbopogon schoenanthus (L.) (Poales: Poaceae), Ocimum americanum L. (Lamiales: Lamiaceae), Securidaca longepedunculata Fres. (Polygalales: Polygalaceae), Synedrella nodiflora Gaertn. (Asterales: Asteraceae), Chromolaena odorata (L.) L. M. King & Robison (Asterales: Asteraceae), Capsicum frutescens L. (Solanales: Solanaceae), Allium sativum L. (Asparagales: Amaryllidaceae) and Carica papaya L. (Brassicales: Caricaceae) have been used in Ghana ( Owusu, 2000, Belmain and Stevenson, 2001, Obeng-Ofori and Ankrah, 2002 and Fening et al., 2011). A study in Uganda revealed that crude aqueous extracts of locally available plants such as tobacco and Tephrosia sp. were as efficacious as Cypermethrin® and Fenitrothion® (synthetic insecticides) in reducing damage caused by bruchid beetle, Callosobruchus sp. in cowpea ( Kawuki et al., 2005). In Nigeria, extracts of garlic, chilli pepper, neem, ginger Zingiber officinale Rosc. (Zingiberales: Zingiberaceae), tobacco, Nicotiana tabacum L. (Solanales: Solanaceae) and sweetsop, Annona squamosa L. (Magnoliales: Annonaceae) have been used to manage field pests of cowpea ( Ahmed et al., 2009).

Farmers who adopt botanicals as a means of plant protection may enhance the activity of natural enemies. For example extracts of neem and Melia azedarach L. (Sapindales: Meliaceae) were sprayed on the parasitoids, Cotesia plutellae (Kurdjumov) (Hymenoptera: Braconidae) and Diadromus collaris (Gravenhorst) (Hymenoptera: Ichneumonidae) in a laboratory bioassay and found not to cause harm ( Charleston et al., 2006). Similarly, application of A. squamosa L. (Magnoliales: Annonaceae) and Aglaia odorata Lour. (Sapindales: Meliaceae) controlled DBM whilst having no negative impact on natural enemies ( Dadang and Prijono, 2009). Ayalew and Ogol (2006) advised that the use of harmful pesticides be discontinued in favour of less harmful ones such as neem-based products to achieve the potential of natural enemies in managing DBM and other pests of crucifers. Reflecting this, DBM was not a major pest of brassicas in China until the early 1960s when large scale application of synthetic insecticides was introduced to commercial vegetable farming ( Liu et al., 2000).
Despite the foregoing potential advantages of botanical insecticides, they have not gained widespread usage globally. The causes of this are complex. Farmers usually want a very rapid knock-down to demonstrate effective application to the crop yet many botanical insecticides operate more slowly and some by modes of action other than toxicity (repellence for example) (Isman, 2006). Second, the availability of many potentially effective botanicals is constrained in many countries by the need to meet expensive regulatory requirements that mean only products that can service a large market are registered. Further, the costs, availability and consistency of plant materials may be a limiting factor. One aspect of this is inconsistent activity of different provenances in the same plant species which can mean that farmers often use plant materials that do not always work (Stevenson et al., 2012). The approach of smallholder farmers preparing their own inexpensive botanical insecticides from locally-available plant materials offers a solution to these problems. The use of botanicals must, however, be economically viable if their potential is to be realised. The plant materials from which botanical insecticides are made are often available locally and are usually obtained without cost (Belmain et al., 2001) making them cheaper compared to their synthetic counterparts. Though the efficacy of various botanical insecticides has been explored in many studies that report pest numbers and, often, effects on natural enemies, there are few reports of the yields from crops treated with botanical insecticides and a dearth of information on the cost:benefit ratios for botanical insecticides compared with conventional insecticide use. This study quantified the costs and benefits of using crude extracts of readily available insecticidal plant materials, an untreated control and a synthetic insecticide in controlling insect pests of cabbage in Ghana.

2. Materials and methods

2.1. Costs

The costs of plant protection were recorded in two field experiments conducted during the major and minor rainy seasons of 2012 at the Crops Research Institute, Kumasi, Ghana. Plant protection treatments of crude extracts of readily available insecticidal plants (botanicals) were compared with the synthetic insecticide, emamectin benzoate (Attack®) and an unsprayed control. Botanicals involved in the study were the goat weed (Ageratum conyzoides L.) (Asterales: Asteraceae), Siam weed (C. odorata), Cinderella weed (S. nodiflora), tobacco (N. tabacum), and castor oil plant (Ricinus communis L.) (Malpighiales: Euphorbiaceae). Most plant materials were collected from weedy, uncultivated areas in the immediate vicinity of the test site and without purchase therefore the associated costs were only labour for the collection, preparation and application plus the value of the soap for extraction. However, since tobacco has commercial value and leaves that could have been sold were used in preparing the extract, the amount that would have been realised from the sale of the leaves was added as a cost in addition to other costs as described above for other botanicals. For plant protection using Attack®, the cost of the insecticide was added to the labour cost of spraying. Throughout the study, labour cost was based on the existing wage for an unskilled labour at the locality at the time of the study which was equivalent to US$ 8.33 per man day. Treatments were prepared as detailed in Amoabeng et al. (2013) and compared in field experiments with four replicates and plot size of 1.5 m × 2.5 m at spacing of 0.5 m × 0.5 m resulting in 24 plants per plot. For the purposes of the economic analyses, values were calculated on a per hectare basis. In the major season, a total of 2 days of labour were used for collecting and preparing the botanicals afresh for each of the botanical treatments. There were six sprayings in the major rainy season whilst the minor season experiment received seven sprayings. This frequency of spraying was used to give comparability with local practice in the use of synthetic insecticides. A total of 18 days of labour was costed for spraying each of the treatments. Sunlight® liquid soap for extraction of each botanical was purchased for US$ 2.00. Attack® was costed at US$ 99.11/ha for six applications.
In the minor season, 14 man days were used for the collection and preparation of each botanical whilst 20 man days were used for spraying. Sunlight® liquid soap was purchased for US$ 2.00 whilst US$ 19.44 was used to purchase tobacco leaves. Cost of Attack® was US$ 122.33 and 20 man days were required for spraying. The externalities such as potential impacts on the environment, natural enemies, and farm worker and consumer safety associated with each of the treatments were not considered in the analyses.
At harvest, plot yields were weighed and recorded. Cabbage heads from each plot were sorted into undamaged or with caterpillar feeding damage, individually weighed and sold at the prevailing price on the local market. The Ghanaian currency, Cedi (¢) was converted to US$ at the prevailing exchange rate of US$ 1: ¢1.8 during the study period. Undamaged heads fetched US$ 0.56 and US$ 0.83 per kg for the major and minor seasons respectively whilst damaged heads fetched one-third of these prices. Revenue was converted to a per hectare basis by extrapolating the plant population of plots based on a plant spacing of 0.5 m × 0.5 m taking into account unplanted alleys to facilitate movement within the field. This resulted in a total plant population of 35,000 per hectare.