Volume 57, March 2014, Pages 71–76
Cost:benefit analysis of botanical insecticide use in cabbage: Implications for smallholder farmers in developing countries
Highlights
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- Cost:benefit analysis compared botanical and conventional insecticide use.
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- Cost:benefit ratios ranged from 1:4 to 1: 29 for botanicals insecticides.
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- Ratios for conventional insecticide were 1:15 and 1:17.
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- For cabbage production in Africa, botanicals are an attractive option.
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- 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.