Push–pull agricultural pest management

Intercropping strategy for controlling agricultural pests

Push–pull technology is an intercropping strategy for controlling agricultural pests by using repellent "push" plants and trap "pull" plants. 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. and national partners. This technology has been taught to smallholder farmers through collaborations with universities, NGOs and national research organizations. (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.

The "push" in the intercropping scheme is provided by the plants that emit volatile chemicals (kairomones) which repel stemborer moths and drive them away from the main crop (maize or sorghum). The most commonly used species of push plants are legumes of the genus Desmodium (e. g. silverleaf Desmodium, D. uncinatum, and greenleaf Desmodium, D. intortum). The Desmodium is planted in between the rows of maize or sorghum, where they emit volatile chemicals (such as (E) β ocimene and (E) 4,8 dimethyl 1,3,7 nonatriene) that repel the stemborer moths. These semiochemicals are also produced in grasses such as maize when they are damaged by insect herbivores, which may explain why they are repellent to stemborers. Being a low growing plant, Desmodium does not interfere with the growth of crops, but can suppress weeds and help improve soil quality by increasing soil organic matter content, fixing nitrogen, and stabilizing soils from erosion. It also serves as a highly nutritious animal feed and effectively suppresses striga weeds through an allelopathic mechanism. Another plant showing good repellent properties is molasses grass (Melinis minutiflora), a nutritious animal feed with tick repelling and stemborer larval parasitoid attractive properties. 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. These effects are thought to be related to isoflavanones produced in Desmodium roots, which can either promote the germination of striga seeds or inhibit seedling growth, depending on their structure. Together, these effects result in the phenomenon known as "suicidal germination", thus reducing the striga seed bank in the soil.

Desmodium also enhances soil quality by increasing soil organic matter, nitrogen content, and soil biodiversity, as well as conserving moisture, moderating soil temperature and preventing erosion.

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. 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. This distrust was fueled by local suspicions that external agents had hidden self interested agendas. 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.

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. 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.