Push–pull technology is a strategy for controlling agricultural pests by using repellent "push" plants and trap "pull" plants.[1] For example, cereal crops like maize or sorghum are often infested by stem borers. Grasses planted around the perimeter of the crop attract and trap the pests, whereas other plants, like Desmodium, planted between the rows of maize, repel the pests and control the parasitic plant Striga. Push–pull technology was developed at the International Centre of Insect Physiology and Ecology (ICIPE) in Kenya in collaboration with Rothamsted Research, UK.[2] and national partners. Research and development for the push-pull strategy was funded by a number of partners including the Gatsby Charitable Foundation of the UK, the Rockefeller Foundation, the UK’s Department for International Development, and the Global Environment Facility of the UNEP, among others.[3] Additionally, research conducted jointly by the International Centre of Insect Physiology and Ecology and Rothamsted Research helped to identify effective companion plants to be used with this strategy and provided empirical evidence of the efficacy of push-pull pest management technology.[3] This technology has further been taught to smallholder farmers through collaborations with universities, NGOs and national research organizations.[3]

The pull [ edit ]

The approach relies on a combination of companion crops to be planted around and among maize or sorghum. Both domestic and wild grasses can help to protect the crops by attracting and trapping the stemborers. The grasses are planted in the border around the maize and sorghum fields where invading adult moths become attracted to chemicals emitted by the grasses themselves. Instead of landing on the maize or sorghum plants, the insects head for what appears to be a tastier meal. These grasses provide the "pull" in the "push–pull" strategy. They also serve as a haven for the borers' natural enemies. Good trap crops include well-known grasses such as Napier grass (Pennisetum purpureum) and Sudan grass (Sorghum vulgare sudanense). Napier grass has a particularly effective way of defending itself against the pests: once attacked by a borer larva, it secretes a sticky substance which physically traps the pest and limits its damage.

The push [ edit ]

The "push" in the intercropping scheme is provided by the plants that emit chemicals (kairomones) which repel stemborer moths and drive them away from the main crop (maize or sorghum). The best candidates discovered so far with the repellent properties are species of leguminous genus Desmodium. Desmodium is planted in between the rows of maize or sorghum. Being a low-growing plant, it does not interfere with the crops' growth and, furthermore, has the advantage of maintaining soil stability, improving soil fertility through enhanced soil organic matter content and nitrogen fixation. It also serves as a highly nutritious animal feed and effectively suppresses striga weeds. Another plant showing good repellent properties is molasses grass (Melinis minutiflora), a nutritious animal feed with tick-repelling and stemborer larval parasitoid attractive properties.

How push–pull works [ edit ]

Push–pull technology involves use of behaviour-modifying stimuli to manipulate the distribution and abundance of stemborers and beneficial insects for management of stemborer pests. It is based on in-depth understanding of chemical ecology, agrobiodiversity, plant-plant and insect-plant interactions, and involves intercropping a cereal crop with a repellent intercrop such as Desmodium uncinatum (silverleaf)[4] (push), with an attractive trap plant such as Napier grass (pull) planted as a border crop around this intercrop. Gravid stemborer females are repelled from the main crop and are simultaneously attracted to the trap crop. Napier grass produces significantly higher levels of attractive volatile compounds (green leaf volatiles), cues used by gravid stemborer females to locate host plants, than maize or sorghum. There is also an increase of approximately 100-fold in the total amounts of these compounds produced in the first hour of nightfall by Napier grass (scotophase), the period at which stemborer moths seek host plants for laying eggs, causing the differential oviposition preference. However, many of the stemborer larvae, about 80%, do not survive, as Napier grass tissues produce sticky sap in response to feeding by the larvae, which traps them, causing the death of about 80% of larvae.[3] Legumes in the genus Desmodium (silverleaf, D. uncinatum and greenleaf, D. intortum), on the other hand, produce repellent volatile chemicals that push away the stemborer moths. These include (E)-β-ocimene and (E)-4,8-dimethyl-1,3,7-nonatriene, semiochemicals produced during damage to plants by herbivorous insects, which are responsible for the repellence of Desmodium to stemborers.

Desmodium also controls striga, resulting in significant yield increases of about 2 tonnes/hectare (0.9 short tons per acre) per cropping season. In the study of the mechanisms of striga suppression by D. uncinatum, it was found that, in addition to benefits derived from increased availability of nitrogen and soil shading, an allelopathic effect of root exudates of the legume, produced independently of the presence of striga, is responsible for this dramatic reduction in an intercrop with maize. Presence of blends of secondary metabolites with striga seed germination stimulatory, 4′′,5′′,-dihydro-5,2′,4′-trihydroxy-5′′,-isopropenylfurano-(2′′,3′′;7,6)-isoflavanone, and postgermination inhibitory,[3] 4′′,5′′-dihydro-2′-methoxy-5,4′-dihydroxy-5′′-isopropenylfurano- (2′′,3′′;7,6)-isoflavanone, activities in the root exudates of D. uncinatum which directly interferes with parasitism was observed. Allelochemicals released by roots of the desmodium lead to suicidal germination, thus reducing the striga seed bank in the soil.[3] Other Desmodium species have also been evaluated and have similar effects on stemborers and striga weed and are currently being used as intercrops in maize, sorghum and millets.[5]

Desmodium also functions to improve soil quality by improving its ability to conserve moisture, increasing biodiversity of the soil, increasing organic matter contained within soil, enhancing fertility because of heightened nitrogen fixation, and, because desmodium serves as groundcover, its presence helps to moderate soil temperature fluctuations.[3]

Economics of push-pull agriculture [ edit ]

Push-pull agriculture leads to beneficial economic outcomes on the level of individual smallholder and subsistence farmers through larger income streams coming from the sale of surplus grain, desmodium seeds, fodder, and milk.[3] Economic study has calculated the return on investment of push-pull methods for farmers to be over 2.2 as compared to 1.8 for pesticide use, and .8 for monocrop.[dubious – discuss][6] Although startup costs of push-pull technology are highly variable due to the requirements of labor to plant desmodium and Napier grass and purchase of these seeds, costs significantly decline in following growing years.[6] Push-pull technology has also been seen to help boost local economies.[3] Because these farmers have more income, they are able to spend money in their local economy which boosts the standards of living and prosperity of the community at large.[3]

The primary economic opponents to such methods are large multinational corporations such as Monsanto and others that produce seasonal inputs such as chemical pesticides, fertilizers and high-yield seeds that require such inputs.[3]

After controlling for extraneous maize yield determinants, it was found that there was a 61.9% maize yield increase with a 15.3% increase in the cost of maize production and a 38.6% increase in the average net income brought in from maize.[7]

In households where push-pull technology has been adopted in Kenya, increased economic earnings have been associated with more years of education, improved access to rural institutions, and attendance to a larger number of field days when compared with households that have not adopted the technology.[7] Additionally, if adoption of the technology continues at the current rate of 14.4%, a reduction of 75,077 people considered poor could be expected in a situation where the local economies remain closed, and 76,504 fewer people could be expected to be considered poor if the economies were open.[7]

Cultural acceptance of push-pull agriculture [ edit ]

Because push-pull technology was developed mainly outside of Sub-saharan Africa—where international agencies today aim to grow its impact the most—a lack of trust was initially faced.[8] This distrust was fueled by local suspicions that external agents had hidden self-interested agendas.[8] In relationships where resources to implement new technologies are also externally provided, farmers often feel that they must simply passively follow the instructions they are given; however, efforts have been made in Ethiopia to encourage farmer engagement with the development of push-pull technology and to thus make the process more collaborative and bridge this gap.[8] Additionally, as mentioned above, push-pull technology is very similar to traditional intercropping methods which has helped it gain community acceptance

Push-pull technology has also been more widely seen as culturally acceptable and congruent because of the way it provides traditional roles for men and women in the agriculture work.[8] Because push-pull technology can fit within existing family frameworks, the practice does not demand an overhaul of existing dynamics.[8] In order to further make the implementation of push-pull technology, farmers played a participatory and influential role in deciding how the technology would be carried out to best suit their needs and align with traditional practices.[8] For example, local farmers preferred to drill the lines in which seeds would be sown using an ox-drawn plough.[8] In general, by promoting the participatory leadership of local farmers, the prospects of sustainability of such projects are anticipated to be strengthened.[8]

Future prospects of push-pull agriculture [ edit ]

This strategy is based around the use of locally available plants, not costly industrial inputs, thus making it both more economically feasible and more culturally appropriate as this method is in many ways similar to traditional African practices of intercropping.[3] For this reason, this method is anticipated to be a popular solution to food insecurity in Sub-Saharan Africa. While this strategy is less resource-intensive, it is more knowledge-intensive.[3] For this reason, mass media campaigns have been launched, public meetings held, printed materials disseminated, and farmer-to-farmer and farmer field school programs established in order to overcome knowledge barriers to the implementation of push-pull technology.[3] The most efficient, influential, and cost-effective methods of disseminating information and encouraging farmers to adopt push-pull methods have been identified to be field days (lead to approximately 26.8% increase in adoption), farmer field schools (22.2% chance of swaying farmers' decisions), and farmer teachers (18.1% chance of convincing farmers to adopt the technology).[6] Additionally, it has been found that over 80% of farmers who participate in field days adopt the technology on their land.[6]

Another measure that has been taken to boost adoption rates of push-pull technology is to distribute desmodium seeds and other inputs that are required to begin this practice.[6] Distribution of seeds and other required inputs has been made possible through partnerships with seed companies and local farmer groups.[6] In order to combat the former shortage and high cost of desmodium seeds that were limiting the spread of push-pull technology, intensive seed production initivatives have been launched and farmer groups have been encouraged to propagate the seeds themselves.[6] As a result of these measures, the market for desmodium seeds has been stimulated and the seeds have become more accessible to smallholder farmers looking to implement push-pull methods in their fields.[6]

In Kenya, Tanzania, and Uganda alone, push-pull technology has been adopted by 68,800 smallholder farmers; however, these numbers may be higher in reality because of gaps in reporting.[6] Because these areas in Sub-Saharan Africa often suffer from unreliable crop production as a result of stemborers and striga, soil infertility, and unsustainable supplies of fodder, the push-pull solution to these problems is expected to be adopted by more smallholder farmers in the future at an annual adoption rate of 30% and a potential annual adoption rate of 50% because of intensive education campaigns that have been launched.[6]

See also [ edit ]