Push-pull biological control involves using certain plants to both attract and repel pests, in this case helping to increase yields of maize crops while reducing the need for harmful pesticides.
Changes in the climate drive shifts in the distribution and numbers of insects, plants and pathogens that are pests for agriculture. The ‘push-pull’ system has been widely implemented in Kenya to reduce loss of maize to pests, leading to increase in yields and net income, and a concurrent reduction in the incidence of poverty. The system works by incorporating two different plant species into the agro-ecosystem, alongside the maize, in order to simultaneously deter and distract pests to reduce pest damage on maize. Napier grass (Pennisetum purpureum) is planted around the border of the field and attracts the stem-borer moth pests away from the maize crop, acting as the ‘pull’. In tandem, desmodium (Desmodium uncinatum) is planted within the maize crop between the rows and releases natural volatile chemicals that repel the pests, acting as the ‘push’. In addition to providing insect control, the push and pull plants can be fed to livestock. Moreover, desmodium is a legume and so fixes nitrogen from the air, increasing the nitrate content of the soil. Furthermore, it also releases chemicals from its roots which prevent germination of a parasitic weed. This push-pull system falls under the umbrella of companion planting, one of several agroecological techniques that harness nature to reduce external inputs and improve agricultural production.
A study of the push-pull system employed across Western Kenya found that average yields of maize were 1573 kilograms per acre in the plots using the push-pull technique, compared with 930 kilograms per acre in those without, showcasing the potential for the system to lead to significantly higher yields. However, it is important to note that, counterintuitively, the push-pull system also required more labor and received more fertilizer inputs in this study. It also reported that the technique resulted in higher milk production from the cows which were fed the fodder, which the study attributed to the increased availability of higher quality fodder for the animals. The study concluded that the push-pull system results in higher productivity and average income increases of 38.6%, possibly translating into reduced poverty and increased household food security.
While not explicitly reported by the study, other studies have found that adoption of the push-pull system tends to result in lower pesticide use, which has been shown to have positive outcomes for ecosystem health and biodiversity in the areas where pesticides would have been used.
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