DOI: 10.1039/b110542f Pest ic ide Outlook – December 2001 233

This journal is © The Royal Society of Chemistry 2001

IntroductionThroughout the developing world, poor rural communitieshave used their knowledge and insight about theirenvironment to improve their livelihoods. Research fundedby the Crop Post-Harvest Programme of the UK Departmentfor International Development is using existing farmerknowledge about botanical pesticides to develop cost-effective and sustainable storage pest control strategies forsmall-scale farmers. Research has provided an under-standing of plant chemistry and modes of action for plantspecies already used by many farmers in Ghana for storedproduct pest control. This has shown that these pesticidalplants can be used reliably and safely to treat grain andlegumes when stored in small quantities at the farm level.Because of their indigenous use in Ghana, legal registrationof these botanical products is not required for theirpromotion in Ghana.

BackgroundSmall-scale farmers throughout sub-Saharan Africa continueto have problems protecting their harvested crops frominsect infestation during storage. Traditional grain storagestructures vary considerably (Figure 1) and are unable toprevent insect infestation. Storage losses are typically patchyand can be a big threat to food security and householdincomes particularly when losses are severe. Because of therisks associated with grain storage, farmers try to minimisetheir losses by selling their grain soon after harvest. Unfortu-nately, since most farmers sell their grain at this time,market prices are low as the market is flooded with recentlyharvested grain. Farmers could achieve a much higher priceif they were to sell their grain later in the season, but theymust control insect infestation of the grain over this timeperiod.

Subsistence farmers often lack the financial resources tobuy good quality commercial insecticides to protect theirstored food, and their inappropriate use of conventionalpesticides can result in risks to human and environmentalhealth and promote insecticide resistance. Traditionalstorage methods using indigenous plants with insecticidalproperties could, if improved, offer a safer, low-cost andmore dependable method of storage protection whilereducing the increasing reliance upon conventionalpesticides. Farmers need this information to support theirdecision making with respect to the reliability of controlthey can expect when using a particular plant material toreduce insect infestation.

Farmer participatory appraisalsThe first step of the research involved conducting ruralassessments in the savannah regions of Ghana (Figure 2) bythe Ghanaian Ministry of Food and Agriculture whichidentified sixteen plant species commonly used by farmersfor stored product protection (Table 1, p 237). The identityof the pesticidal plants was confirmed against the typespecimens at the Royal Botanic Gardens, Kew, UK. This wasextremely important because sometimes several locallanguage names could refer to the same plant species, or asingle local name could refer to several plants with similarcharacters or from closely related genera.

ETHNOBOTANICALS IN GHANA: REVIVING AND MODERNISINGAGE-OLD FARMER PRACTICE

Steve Belmain and Phil Stevenson from the Natural Resources Institute in the UK describe how farmers’indigenous knowledge has improved grain storage practice through botanical pesticides and how it can beoptimised through understanding the modes of action of the active components

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Figure 1 Structures for storing harvested grain and legumesvary considerably depending on availability of materials. Moststorage structures have a thatched roof and walls made fromwoven grass and/or sticks which may or may not be coveredwith mud.

The way farmers were reported to use the plants variedconsiderably. Some farmers would make a hot water extractof the plant which they would pour over their commodity oruse as a grain dip (Figure 3). Some farmers used the plantmaterial as whole flowers or leaves, whereas others wouldgrind the material into a powder (Figure 4). The amount ofmaterial used to treat the commodity also varied, and somefarmers would admix the botanicals while others wouldlayer it with their commodity. The plant parts used for anygiven species varied the least, and, generally, all farmersconsistently used the same plant parts (e.g. leaves, roots,flowers) for a particular plant species. The main differencesfound in application methodology illustrated howinnovative and experimental farmers could be, but it alsohighlighted that communication between farmers may be aproblem as no single method was markedly more popularthan another. It was, therefore, necessary to determine themost effective application method to control storage pests.Research, discussed below, was designed to investigate theefficacy of control through laboratory and field-based trialsamong the different plant species and among differentapplication methods.

From the beginning of the project, efficacy wasrecognised as only one of the factors that farmers wouldconsider when choosing a method of pest control. So duringthe appraisal surveys, farmers were asked to assess thecontrol strategies they use according to how they influence

their choice of pest control options. Plant species andcommercial synthetics were assessed by farmers for theircost, effectiveness, availability, toxicity, ease of use, accept-ability and versatility. These criteria were ranked, and theresults indicated that cost was far more important thanefficacy. Furthermore, some plant materials were preferredover others, depending upon their availability or ease of use.In all, more than 500 farmers were surveyed from differentvillages across northern Ghana, and all the farmers rated theuse of plant materials favourably in comparison to com-mercial synthetics. Most farmers highlighted the prohibitivecosts of using commercial synthetics but expressed equalconcern towards the toxicity of synthetic pesticides. Safety

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Figure 2 The map of Ghana indicates the northern area(outlined in green) which was surveyed for indigenous post-harvest practices using plant materials with insecticidalproperties. In all, more than 500 farmers were surveyed from45 villages spread around the Northern, Upper East andUpper West Regions.

Figure 3 Many farmers extract pesticidal plants in hot water.The extract is then poured over the commodity or thecommodity is dipped into the extract, and the commodity isthen dried in the sun before storage. Laboratory and fieldtrials found that this method was largely effective due to thehot water and the sun drying which killed off any existinginfestation in the commodity. Although research has indicatedthat many of the active constituents found in the plants arewater soluble, the concentration applied by quickly dippingthe commodity into the extract is very low. However, this maybe sufficiently repellent to prevent re-infestation of the grain

Figure 4 The most common method for using pesticidal plantsfor stored product protection is pounding the plant to apowder and admixing this with the commodity. This islaborious work, but research indicates it is the most effectivemethod of applying botanicals for stored product protection.

issues arise because farmers in many developing countriescan not always be sure that the pesticides they buy are thecorrect pesticide for the job or whether they have beenadulterated. Although it could be argued that ‘natural’botanical pesticides may also be toxic to humans, they are atleast of known quantity, and farmers feel more comfortablewhen using them for the same reasons that most consumerswould consider a ‘natural’ product to be safe.

In discussion with farmers and rural communities, oursurvey showed that 74% of villages in the three northernregions visited used botanicals as storage protectants.However, the use of plant materials was concentrated in theUpper East Region where the number of farmers usingbotanicals was 95%. These distinctions in prevalence of usagetend to be attributable to ethnic and cultural differences inindigenous knowledge (Cobbinah et al., 1999). Promotingbotanical use through institutions such as the GhanaianMinistry of Food and Agriculture may provide a way toreach a wider audience by spreading knowledge acrosscultural barriers.

Confirming efficacySome plants used for post-harvest storage protection inGhana had already been studied for various pesticidal andmedicinal uses. For example, chilli peppers and orange peelare well-known botanicals for post-harvest protection (Onu

and Sulyman, 1997; Lale, 1992). The neem tree,Azadirachta indica, is probably the most well-knownbotanical and is used widely throughout Asia and Africa fora variety of medicinal and agricultural uses (Puri, 1999;Narwal and Tauro, 1997) (Figure 5). However, literaturereviews indicated that some of the plants identified in oursurvey were virtually unknown. So their efficacy neededconfirmation through standardised laboratory and fieldstudies. These initial trials were conducted following themethods by which farmers in Ghana already used the plantsfor stored product protection. Methods were furtherdeveloped by admixing powdered plant materials at differentconcentrations with the test commodity and subsequentlyinfesting with the major insect pests of stored cereal grainsand legumes. Both laboratory and farmer participatoryresearch trials showed that some plants were found to belargely ineffective at reducing infestation, and these weresubsequently dropped from our research activities.

Our trials showed that the efficacy of different plantspecies was not correlated with the prevalence of use byfarmers. In other words, the abundance of the plantsgrowing in the natural environment and other markercriteria were important factors in how widely a plant wasused by farmers. For example, trials showed that the plantmaterial most effective in controlling storage insects wasSecuridaca longepedunculata, but this was not the mostwidely used plant by farmers. Evidence collected throughdiscussions with farmers and from habitat abundancesurveys conducted by the Ghanaian Forestry ResearchInstitute indicated that plants such as S. longepedunculatawere increasingly rare in the environment due to over-collection, unsustainable harvesting methods, uncontrolledbush fires and poor plant propagation characteristics.Similarly, some of the more widely used plants for storedproduct protection were not always highly effective but wereeasily collected from abundant natural habitats.

Farmer participatory researchOver the past five years, farmer participatory trials havebeen conducted over the storage season. About 200 farmersfrom the Northern and Upper East Regions have beeninvolved each year testing the efficacy of the botanicalsunder farmer storage conditions using their own harvestedcommodities. These trials have also been a way of gatheringfeedback from farmers on which plants they think areworking best and gauging how other factors influence pestcontrol (Figure 6).

Depending on when and how farmers harvest their grain,insect infestation can occur before it is put into storage.Initial levels of pest infestation can, therefore, vary consider-ably among farmers, and this has a large impact upon howwell botanical treatments work. Botanicals are a complexmix of compounds that may be acting in different ways onthe target pest which can impact upon the choices a farmermakes. For example, if initial insect infestations are high, afarmer should perhaps choose a plant which causessignificant adult mortality. However, with relatively cleangrain a farmer may opt for a plant material which is largelyrepellent to insects. Because recommendations made to

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Figure 5 Neem leaves, Azadirachta indica, being stripped fromthe stem and shade dried. The dried leaves will then bepounded and admixed at between 2–5% with commodity, thehigher the concentration the more effective and long-lastingthe protection offered.

farmers need to be simple and trustworthy, a series ofexperiments were conducted which aimed to understandmore specifically how the plant materials worked in thestorage environment. Natural variability of secondarymetabolites found within plants could affect the reliability ofcontrol experienced by farmers. For example, anecdotalinformation indicated that some plants work only inparticular regions while not in others. We, therefore, neededto establish whether this was because different species weregrowing in different regions or that the active ingredientswere not present in plants collected from different areas.Through analyses conducted by the Royal Botanic Gardens,Kew and the Natural Resources Institute, all the botanicalsshowed significant phytochemical changes, both quantita-tively and qualitatively, according to harvest location,season and, not surprisingly, plant part. However, phyto-chemical variability did not appear to effect overallbioactivity with regard to stored product pest control. Asthe bioactive constituents are not well-known for each plantspecies, it may be inappropriate to make correlationsbetween phytochemical variability and bioactivity. Throughthis research, the mode of anti-insect activity of the plantmaterials has been shown to be important. For some of thespecies, such as Cymbopogon schoenanthus, the plant ishighly repellent but not particularly toxic to insects, and

despite its lack of toxicity, it is still effective in protectingfarm stored grain as demonstrated in farmer participatorytrials (Levinson and Levinson, 1999). Repellent plants mayindeed be preferable because their human toxicity could beargued to be lower than an outright insecticidal plant.

SafetyIt should not be assumed that just because the botanicalpesticides are naturally derived that they are safe to use andconsume by humans, and some form of safety assessmentneeds to be considered. In order to assess their mammaliantoxicity, some of the more promising plant species weretested for toxic effects against vertebrates (Belmain et al.,2001). Research conducted by the UK Medical ResearchCouncil showed that rodents expressed no symptoms oftoxicity when plant materials were incorporated into theirdiets over a six-week period with the exception ofSecuridaca longepedunculata and Chamaecrista nigricens,which gave some indication they could be harmful ifingested at high concentrations over prolonged periods oftime. Many of the plants used for stored product protectionhave alternative uses as medicines or food spices, indicatingthat any serious vertebrate toxicity would have beenestablished through the development of the ethnobotanical

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Figure 6 Optimising how plant materials are used for stored product protection involves LEFT) giving farmers a choice on whichplants they will use during research trials they will manage in their own store using their own commodity. RIGHT) The plantmaterials being offered as choices to this farmer are (clockwise from top left) Cassia sophera, Securidaca longepedunculata,Ocimum americanum, Lippia multiflora, Synedrella nodiflora and Azadirachta indica.

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Table 1 The sixteen plant species below are commonly used by farmers in the north of Ghana for stored productprotection. Species marked with an ‘*’ remain the focus of further research on pesticidal plants which have beenselected through laboratory and field research that showed them to offer good insect pest control.

Latin name Method of use cited by farmers Mitigating factors Prospects for increased promotion

Azadirachta indica* Most farmers use leaves, using either Chemistry and bioactivity of leaf Excellent, widely available, large body offresh or dried whole leaves, leaf material highly variable research showing good quality control,powder, a paste or water extract, depending on collection time powdered leaves better than water admixed or layered. Many other uses and place extract of leavesas medicines, crop pesticides, soap

Although seed oil is recognisedto be more effective, few farmersuse seeds because it’s laboriousand smelly to process

Capsicum annuum* Whole or powdered chillies admixed Unacceptable levels of grain Excellent. Good quality control,or layered tainting for some purposes commonly grown as a spice

Cassia sophera* Powdered leaves and seeds. Also used Chemistry and bioactivity highly Excellent. Widely prevalent with goodas green manure and as a supplement variable depending on collection quality of controlto animal fodder and ethnoveterinary time and placeuses

Chamaecrista nigricens* Powdered leaves, admixed or placed Reduced availability as plant Good. Propagation reduced due to at top and base. Veterinary and suffers from over-collection savannah fires and high usage. medicinal uses. Sometimes sold in Environmental protection and/or markets cultivation required

Citrus sinensis* Orange peel dried, powdered and Expensive in north of Ghana Good. Cost-effective only in areas admixed as oranges are imported from where citrus is grown. More effective

the south against legume pests than grain pests

Combretum spp. Powdered leaves. Also used as green About 20 species of the genus Poor. Low efficacy, dropped frommanure and as a supplement to found growing within the same further trials. Taxonomic confusion may animal fodder. habitat with similar anatomical be responsible for variable effects

characteristics experienced by farmers

Cymbopogon Whole or powdered flower heads Reduced availability as plant Good. High demand increases scarcity,schoenanthus* or entire plant. Sometimes sold in suffers from over-collection but is relatively easy to propagate

markets. Used as a mosquito repellent

Khaya senegalensis Powdered bark admixed Bark harvesting often leads to Poor. Although excellent control, tree death difficulty in policing patch bark harvesting,

and conservation priorities prevent itspromotion

Lippia multiflora* whole leaves and/or flowers, Good. Restricted habitat range, efficacyadmixed or layered lost within three months

Mitragyna inermis Whole or powdered leaves admixed Poor. Low efficacy, dropped fromor layered further trials

Ocimum americanum* Whole or powdered mature plants, Good. Widely prevalent but efficacyadmixed or layered. Ceremonial and lost within three monthsmedicinal uses

Pleiocapa mutica Powdered leaves. Also used as a Poor. Low efficacy, dropped fromsupplement to animal fodder. further trials

Pterocarpus erinaceus Powdered leaves or roots admixed, Poor. Low efficacy, dropped from water extract of leaves or roots. further trialsLeaves often used as a supplement to animal fodder.

Securidaca Water from soaked roots, admixed Reduced availability as plant Good. Quality of control excellent butlongepedunculata* powdered root bark. Many other uses, suffers from over-collection harvesting of roots results in high plant

including water purification, ceremonial, mortality and reduced natural medicinal, washing clothes. Sometimes propagation. Ongoing research to sold in markets. cultivate the plant may improve

prospects.

Synedrella nodiflora* Water from boiled leaves and flower Excellent. Widely prevalentheads, poured or immersed 20-30 sec., powdered leaves and flower heads. Often burned inside houses as a mosquito repellent

Vitellaria paradoxa* Seed oil or oil extraction residue admixed Oil predominantly used for cooking. Good. Only for legume pests, best controlOil extraction is laborious but often by using residue plus a small quantitydone to provide cooking oil. of oil

knowledge. The risk of consuming larger quantities ofbotanicals through storage protection would be reducedthrough winnowing, washing, processing and cooking. Werecommend further research investigating potentialbotanical residue levels on treated food after processing andcooking before the institutional promotion of botanicals forstored product protection begins.

Future ProspectsEvidence collected from small-scale farmers indicates thatthey prefer pesticidal plant materials over other forms ofpest control during storage. However, individual farmerknowledge about different plants and how best to use themvaries considerably. Research to date has been able tonarrow down the list of plants, focussing upon those thatwork best and optimising their application methods for on-farm storage use. It is hoped that this new knowledge can bewidely disseminated to farming communities through part-nerships with NGOs and farmer extension programmesoperated by the Ghanaian Ministry of Food and Agriculture.One issue which remains unresolved is the accessibility andavailability of the plant materials. This does affect farmerchoices. Most of the plants are collected from the wild andsome species are suffering from over-collection and environ-mental degradation. In order for these plants to be usedsustainably, we hope to investigate their propagation andcultivation potential as well as their conservation in thewild. Some of the species such as Azadirachta indica andSynedrella nodiflora could be considered weeds, and theirinvasive properties and prolific regeneration imply thatneither plant is likely to become threatened. However, manyof the species are potentially vulnerable with regard to theirregeneration potential, showing sporadic and patchy growthdue to widespread and uncontrolled annual fires. Promotionof botanicals will ultimately assist biodiversity conservationof the savannah by increasing its perceived value.

Research at the Natural Resources Institute and theRoyal Botanic Gardens, Kew continues to isolate andidentify the active constituents from some of the less well-known plant species. This information can principally beused to help assess the safety of the botanicals as well astheir optimal application methods. By knowing more aboutthe phytochemistry of the plants we may be also able toidentify other plant species which share the activeconstituents, thereby reducing collection pressures on tradi-tionally collected species. The identification of novelcompounds or modes of action found in the botanicalscould lead to the development of new commercial productsfor the wider benefit of humanity and the country of origin.

AcknowledgementsFunding for this research was obtained from the Crop Post-Harvest Programme of the United Kingdom’s Departmentfor International Development. The authors would like toacknowledge that this research has been conducted incollaboration with many scientists based with the RoyalBotanic Gardens, Kew, UK, the Medical Research Council,UK, the Ministry of Food and Agriculture, Ghana, theUniversity of Ghana and the Forestry Research Institute,Ghana.

References and further readingBelmain, S. R.; Neal, G E.; Ray, D. E.; Golob, P. (2001) Insecti-

cidal and vertebrate toxicity associated with ethnobotanicalsused as post-harvest protectants in Ghana. Food and ChemicalToxicology, 39(3), 287–291.

Belmain, S. R.; Golob, P.; Andan, H. F.; Cobbinah, J. R. (1999)Ethnobotanicals – future prospects as post-harvest insecticides.Agro Food Industry Hi-tech., 10(5), 34–36.

Cobbinah, J. R.; Moss, C.; Golob, P.; Belmain, S. R. (1999)Conducting ethnobotanical surveys: an example from Ghana onplants used for the protection of stored cereals and pulses. NRIBulletin, #77. Natural Resources Institute, Chatham, UK. ISBN0859545024.

Dales, M. (1996) A review of plant materials used for controllinginsect pests of stored products. NRI Bulletin, #65. NaturalResources Institute, Chatham, UK. ISBN 0859544206.

Golob, P.; Moss, C.; Dales, M.; Fidgen, A.; Evans, J.; Gudrups, I.(1999) The use of spices and medicinals as bioactive protectantsfor grains. FAO Agricultural Services Bulletin, #37. Rome, Italy:FAO Publications. ISBN 9251042942

Lale, N. E. S. (1992) Oviposition-deterrent and repellent effects ofproducts from dry chilli pepper fruits, Capsicum species onCallosobruchus maculatus. Postharvest Biology and Technology.1(4), 343–348.

Levinson, H.; Levinson, A. (1999) Pest control of stored grain inantiquity. Informatore Fitopatologico, 49(9), 13–18.

Misra, H. P. (2000) Effectiveness of indigenous plant productsagainst the pulse beetle, Callosobruchus chinensis on storedblack gram. Indian Journal of Entomology. 62(2), 218–220.

Muda, R.; Cribb, B. W. (1999) Effect of uneven application ofazadirachtin on reproductive and anti-feedant behaviour ofRhyzopertha dominica (Coleoptera: Bostrichidae). PesticideScience. 55(10), 983–987.

Narwal, S. S.; Tauro, P (eds.) (1997) Neem in sustainableagriculture. Scientific Publishers. Jodphur, India.

New Agriculturist (2000) Plants as protectants against storagepests. http://www.new-agri.co.uk/00-3/focuson/focuson4.html

Onu, I.; Sulyman, A. (1997) Effect of powdered peels of citrusfruits on damage by Callosobruchus maculatus (F.) to cowpeaseeds. Journal of Sustainable Agriculture, 9(4), 85–92.

Puri, H. S. (1999) Neem. The divine tree Azadirachta indica.Medicinal and Aromatic Plants, Vol. 5. Harwood AcademicPublishers, Amsterdam, Netherlands.

Sharma, R. K. (1999) Efficacy of neem products against storagepests in maize. Annals of Agricultural Research, 20(2), 198–201.

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