Plants as protectants against storage pests
Plant materials with insecticidal properties provide small-scale farmers with a locally available, biodegradable and inexpensive method of pest control for storage. Botanicals, such as neem and hot chilli pepper, have been used for generations throughout Africa, Asia and the Americas. However, surveys conducted by NRI in Ghana have revealed that many farmers are unaware of the use of insecticidal plants despite their use by farmers in other areas and regions. In fact, the majority of farmers do nothing to protect their grain during storage largely because resource-poor farmers find conventional synthetic pesticides too expensive and difficult to obtain. Furthermore, inappropriate use of synthetic chemicals may lead to human and environmental health risks and promote insecticide resistance.
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| Credit: S.R.Belmain, NRI |
Botanicals could, therefore, have advantages over synthetics as a cost-effective and environmentally sustainable alternative for protecting stored food against insect attack. However, information and scientific support on botanicals is generally inadequate, and it is often difficult to recommend particular plant materials as a replacement for chemical insecticides as the efficacy levels of botanicals can vary among storage pests, application methods, and stored products.
Through participatory surveys conducted in Ghana, researchers at NRI, in collaboration with the Ghanaian Ministry of Food and Agriculture, have identified seventeen different plant species which are used by farmers as storage protectants, eight of which are commonly used throughout the northern areas of Ghana. Further research is currently being conducted to understand the mechanisms of bioactivity in the identified plants in order to provide farmers with low-cost alternatives to synthetic pesticides for controlling storage pests at farm-level.
Research on these ethnobotanicals is focused on poor farming communities, who are already familiar with indigenous plants for pesticidal or medicinal properties (see Focus On Essential Extracts 00-2). Although surveys have identified that many farmers believe botanicals are cheap, available and thought to be safer than conventional pesticides, there is also evidence that a lack of understanding prevents their widespread uptake. For example, Chromolaena odorata (siam weed) is sometimes mixed with stored grain to control common storage pests, such as the Larger Grain Borer (Prostephanus truncatus) and maize weevil (Sitophilus zeamais), but the opinion of farmers regarding its efficacy has been shown to vary. C.odorata and Azadirachta indica (neem), although both commonly used for their insecticidal properties, are more often recognised for their medicinal properties. Young, literate farmers who are more well-informed about present day storage methods showed a greater tendency to use botanicals as storage protectants although the knowledge base about botanicals was more common in older males. It is hoped that technology transfer among villages and villagers could result in greater efficacy of pest control using insecticidal plants.
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| Credit: S.R.Belmain, NRI |
Laboratory and field trials have shown that the most effective plant material with indigenous use in Ghana as a storage protectant was Securidaca longipedunculata (locally known as palaga) although this plant was not widely used by farmers. The reason for its limited use is not known but may be related to its availability or ease of use. Medicinal uses of S.longipedunculata have been reported in other regions of Africa so the plant should be relatively safe to use although data on potential vertebrate toxicity is lacking. Some of the other Ghanaian plant materials tested also showed toxicity, including neem and chilli (Capsicum annuum), or repellency against some or all of the insect species tested. With some insecticidal plant species, dipping the grain or legumes into a hot water extract appeared to be more effective than admixing powdered plant material, both methods being commonly practised by farmers using plants as storage protectants.
Whilst these results are encouraging, there are still questions to be answered about the use, safety and effectiveness of these plants as storage protectants. To increase the quality and reliability of pest control when using these botanicals, further research involving field trials and farmer participatory trials is currently being conducted under local conditions in Ghana. Ultimately, it is hoped that these research findings will provide recommendations for sustainable, natural alternatives to synthetic pesticides for poor farming communities in Ghana and other regions where these plants are known to occur.
Further information:
The use of spices and medicinals as bioactive protectants for grain
(see In Print)
A review of plant materials used for controlling insect pests of stored
products, NRI Bulletin 65, 1996, ISBN 0859544206 £10.00
Conducting Ethnobotanical Surveys: an example from Ghana on plants
used for the protection of stored cereals and pulses, NRI Bulletin
77, 1999, ISBN 0859545024 £5.00
Note: NRI Bulletins available from CAB International Email: orders@cabi.org
or http://www.cabi.org/bookshop
