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Boosting cashew production in Ghana
Kwame S Aidoo, Department of Entomology & Wildlife, School of Biological Sciences, University of Cape Coast, Ghana
Keywords: Africa, Apis mellifera, biological control agent, pollinator, solitary bee, stingless bee
Investigation of the genetic composition of cashew trees and their pollinators in Ghana revealed the country to have productive advantage over other cashew growing countries of the world. When Kwame Aidoo presented his PhD thesis to a panel of academics of the University of Cape Coast, he challenged the National Cashew Project and other organisations to extend their research findings to farmers. An extension package consisting of high yielding planting material with multiple genetic composition, good cultural practices that improve pollinator presence in orchards, and the use of red ants Oecophylla longinoda as biological control agents of pests, will further improve cashew production. The study revealed that high yielding trees with multiple genetic compositions are present in many orchards in Ghana, and these should be selected and developed as seed resources for farmers.
The climatic conditions and soil characteristics of the cashew areas of Ghana are good. Rainfall is the most important climatic factor for cashew crop productivity and total annual rainfall in all major growing areas in Ghana are ideal. The long dry season from November to April gives the cashew crop the right conditions for flower initiation and fruit development.
Pollinators of the cashew tree
The honey bee Apis mellifera has been described by many pollination biologists as the most effective pollinator of cashew (Free & Williams, 1976; Heard et al, 1990). This study showed that honey bee workers infrequently foraged on cashew flowers, but when they did, they spent a relatively short time collecting only nectar. On any hermaphrodite flower there was a 50 : 50 chance of the honey bee worker effecting pollination. This suggests that Apis mellifera is not the most effective pollinator of cashew orchards in Ghana as found in other cashew growing areas of the world. The study identified two stingless bees: Dactylurina staudingeri and Liotrigona parvula and seven solitary bees Brausapis sp, Ceratina sp, Compsomelissa sp, Halictus sp, Lasioglossum sp, Lipotriches sp and Thyreaus sp whose foraging activities indicated their effectiveness in the pollination of cashew. These two groups of bees are known to be heavy feeders of pollen, and were found to be persistent foragers, and exhibited behavioural characteristics which demonstrated their strong affinity to cashew flowers. The cashew plant's ability to produce large amounts of pollen is probably to attract pollen rather than nectar foragers. These bees therefore are the effective pollinators of cashew flowers in Ghana. The abundance and diversity of the right pollinators in the cashew agro-ecosystem gives Ghana a comparative advantage over other growing countries. The presence of various forms of natural landscapes provided good sanctuaries for pollinating bees and other beneficial insects. Studies in Brazil recorded only two bees Apis mellifera and Chrysogaster tarsata as effective pollinators of cashew flowers (Freitas et al, 2002). Heard et al (1990) found Apis mellifera as the only bee pollinating cashew efficiently in northern Australia. Seven bee species effectively pollinate cashew trees in Ghana. Their pollinating activities were supplemented by Apis mellifera and occasional flower visitors such as ants, butterflies, sun birds and wasps.
Pests and cashew production
Investigations into the performance of cashew farms revealed that in some areas, most farms had been abandoned. Some farmers had felled their cashew trees for fuel wood and were instead cultivating food crops. In Mfantsiman District, 55 out of a total of 60 farmers had abandoned their orchards. In Komenda District 115 farmers established about 93 ha of cashew and in Gomoa District, 350 farmers developed about 324 ha farms. It is estimated that 90% of these farms have been abandoned. Farmers attributed their actions to the fact that cashew nut yields on their farms were so poor that they were not making economic gain.
These low yields are due to uncontrolled activities of insect pests, the major ones being Anoplocnemis curvipes, Helopeltis schouteden and Pseudotheraptus devastans. The feeding activities of these cashew bugs had serious effects on productivity. Young shoots which otherwise would have produced flower panicles die back, fruits at varying stages of development drop off, and nut yields become low. Other insect pests such as the cashew stem borer beetle Apate telebrans and the branch girdler Analeptes trifaciata were active on some farms.
Oecophylla longinoda was identified as a potent natural control agent for many insect pests in cashew plantations. The introduction and establishment of colonies of Oecophylla longinoda on farms in Brong Ahafo is helping to deal with cashew pest problems. Farmers did not use chemical pesticides but their orchards were comparatively healthier and produced higher nut yields. The cost of orchards management with Oecophylla longinoda was lower and net returns high.
Nut yields of 1,250 kg per hectare were recorded in plantations of Ejura Farms Company in Ashanti. This was higher than the world's top yield of 1,000 kg per hectare (Kannan, 2002). The lowest average yield of 303 kg per hectare was recorded in the northern region. Even this figure was higher than Brazil's national average of 192 kg per hectare (Freitas & Paxton, 1998). Good cultural practices, especially with respect to pest control in Ashanti and Brong Ahafo, coupled with relatively better ecological conditions contributed to these higher yields.
Ghana has great potential in the development of cashew as a crop of importance equal to cocoa. The major growing areas of the country were found to have good ecological conditions for optimum productivity. Many species of bees were found inhabiting various natural landscapes that adjourned orchards and these provided the essential pollination services. These bees supported the natural mating system of cashew orchards that were characterised by broad based heterozygous trees. Nut yields of orchards were comparatively higher than other production areas of the world. The activities of insect pests in orchards were identified as one of the main factors which reduced nut yields to levels where many farmers abandoned their farms. The pest problem in orchards could best be controlled effectively by utilising the predatory activities of Oecophylla longinoda as demonstrated by farmers in Brong Ahafo.
It is recommended that cashew farmers and/or researchers should:
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