Pennisetum purpureum, also known as Napier grass, elephant grass or Uganda grass, is a species of perennial tropical grass native to the African grasslands. It has low water and nutrient requirements, and therefore can make use of otherwise uncultivated lands. Historically, this wild species has been used primarily for grazing; recently, however, it has been incorporated into a pest management strategy. This technique involves the desired crop being planted alongside a 'push' plant, which repels pests, in combination with a 'pull' crop around the perimeter of the plot, which draw insects out of the plot. Napier grass has shown potential at attracting stemborer moths (a main cause of yield loss in Africa) away from maize and hence is the "pull" crop. This strategy is much more sustainable, serves more purposes and is more affordable for farmers than insecticide use. In addition to this, Napier grasses improve soil fertility, and protect arid land from soil erosion. It is also utilized for firebreaks, windbreaks, in paper pulp production and most recently to produce bio-oil, biogas and charcoal.
Pennisetum purpureum is a monocot C4 perennial grass in the Poaceae family. It is tall and forms in robust bamboo-like clumps. It is a heterozygous plant, but seeds rarely fully form; more often it reproduces vegetatively through stolons which are horizontal shoots above the soil that extend from the parent plant to offspring. This species has high biomass production, at about 40 tons/ha/year and can be harvested 4-6 times per year. Additionally it requires low water and nutrient inputs.
Napier can be propagated through seeds, however as seed production is inconsistent, collection is difficult. Alternatively, it can be planted through stem cuttings of the stolons. The cuttings can be planted by inserting them along furrows 75 cm apart, both along and between rows.
Push Pull Pest Management Strategy
Stemborers (Busseola fusca and Chilo partellus) are the cause of 10% of total yield loss in Southern and Eastern Africa and on average 14-15% in sub-Saharan Africa. The larvae cause immense damage to maize and sorghum by burrowing into their stems and eating from within. This not only makes them difficult to detect and remove but also damages the vascular tissue necessary for plant growth. Insecticide effectiveness is low against stemborers, as larvae are protected by protective cell wall layers around the stem. Insecticides are also expensive for poor farmers and can build chemical resistance by the pests. In addition, chemicals are carried into final food products. Instead of trying to prevent the occurrence of pests, the push-pull strategy (also known as stimuli-deterrent) aims to guide their inevitable biological evolution to prevent damage to valued crops. The method proposes that sorghum or corn be intercropped with Desmodium (the "push" plant), which repels the moths as they look to lay their eggs. Desmodium also provides a ground cover and is nitrogen fixing, which improves soil fertility while decreasing labour involved with weeding. This deterrent is used in combination with Napier grass planted around the perimeter of the plot. A study of Kenyan farmers using the push-pull strategy reported an 89% reduction in Striga (a parasitic weed), an 83% increase in soil fertility, and 52% effectiveness in stemborer control. Considering that striga, stemborers, and low soil fertility together cause yield losses of an estimated 7 billion US dollars or enough to feed 27 million people, the implementation of this technique could significantly reduce food insecurity.
Push-pull pest management
Although promising as a sustainable and affordable option, the success of push-pull pest management highly depends on proper implementation in combination with other good ecological practices. Firstly, not all varieties of Napier grass function as a trap. In a study of eight varieties, only two bana and Ugandan hairless Napier varieties significantly attracted female moths for egg placement over maize. Of these two, only bana significantly decreased survival rates. In a farmer's field, it is recommended that three rows of bana Napier grass be planted as a border crop around the entire field. Potential exists to improve the push-pull strategy through further trials with different intercrops, by manipulating allelochemicals in each intercrop, as well as by investigating insect sensitivity to natural chemicals. Once prominent in a field, it is difficult to rid the area of the stemborer pests as larvae can remain dormant, and therefore push-pull management will not have the intended effect. It is recommended that if an infestation is particularly severe, neither corn, nor sorghum should be planted in the same field the following year but instead rotated with other crops. It is also important to burn infested stalks or, if they have an intended use, to leave them out in the sun for three days. The use of push-pull pest management must be used in combination with good ecological practices to yield the desired results. Finally, the establishment of a push-pull system requires increased labour in the primary stages and a large enough land plot to allow space for a non-food crop to be planted; these factors often deter its adoption. A program could increase adoption rates through promoting its use in combination with livestock, giving economic value to the planting of Napier. More information can be found at http://www.push-pull.net/ as well as specifics for implementation at http://www.push-pull.net/farmers_guide_2012.pdf .
Napier grass is the most important fodder crop for the dairy farmers in East Africa. Hairless varieties, such as Ugandan hairless, have much higher value as fodder. As it is able to grow with little water and nutrients, grazing has made productive use of arid lands for food production. Furthermore, livestock can be incorporated into the pull-push management system providing another economically viable purpose for the ‘trap’ plant. Napier grass is valuable to African landscapes as it prevents soil erosion. It can also serve as a fire break, a wind break, and to improve soil fertility. More recently, Napier has been used to alleviate pressure on food production as there is 2Gha of non-arable land suitable for energy crop production. Thermal pyrolytic conversion is used to produce charcoal, biogas and bio-oil. Although this technology is not currently in use, it could be implemented as a means of providing energy to African communities, while enriching the soils of the local landscape. It is also used as source of fuel.
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- [Khan, Z. R., Midega, C. A. O., Wadhams, L. J., Pickett, J. A., & Mumuni, A. (2007). Evaluation of Napier grass (Pennisetum purpureun) varieties for use as trap plants for the management of African stemborer (Busseola fusca) in a push-pull strategy Entomologia Experimentalis et Applicata, 124, 201-211.]
- [Khan, Z. R., Midega, C. A. O., Wadhams, L. J., Pickett, J. A., & Mumuni, A. (2007). Evaluation of Napier grass (Pennisetum purpureun) varieties for use as trap plants for the management of african stemborer (Busseola fusca) in a push-pull strategy Entomologia Experimentalis et Applicata, 124, 201-211.]
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- [Khan, Z. R., Amudavi, D. M., Midega, C. A. O., Wanyama, J. M., & Pickett, J. A.(2008). Farmers' perceptions of a 'push-pull' technology for control of cereal stemborers and striga weed in western Kenya. Crop Protection, 27, 976-987.]
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