One of the most effective agronomic approaches of Intergrated Pest Management (IPM) is the “push-pull” system, built on the concept of polyculture (agriculture using multiple crops in the same space), that protects maize, millet and sorghum from two devastating pests: the stem borer insect and the Striga weed. Push-pull entails mixing plants that repel insect pests (“push”) and planting diversionary trap plants around a crop perimeter which attract the pests away from the crop (“pull”). In the case of maize, millet and sorghum, the main cereal crop is intercropped with the forage legume Desmodium. Desmodium emits volatile chemicals that repel stem borer moths (“push”) and attracts a natural enemy of the moths, parasitic wasps (“pull”).
In addition, Desmodium secretes chemicals from its roots that cause “suicidal” germination of Striga seeds before they can attach to the maize roots. To ensure further protection, farmers can plant a “trap crop,” such as Pennisetum purpureum (also known as Napier grass) around the edge of the field, which attracts the moths, pulling them away from the main crop. The system was developed in collaboration with the International Centre of Insect Physiology and Ecology (ICIPE) and the Kenyan Agricultural Research Institute (KARI) in Kenya, and Rothamsted Research in the United Kingdom. As of 2010, 25,000 smallholders in East Africa are using push-pull systems. Adopting a push-pull system allows them not only to control pests but also to increase soil fertility, protect against erosion, reduce pesticide use and gain income from marketing Desmodium for animal fodder.
In 2014, Greenpeace researchers interviewed three sets of farmers from Kitale and Mbita, Kenya: those practicing push-pull, those using pesticides, and those using neither approach. Although based on only a small number of interviews, average profitability per acre of maize per year was found to be 3 times higher for push-pull farmers than non-push-pull farmers, and this effect was even greater (up to 4 times more profitability) for women. Farmers also reported that maize yields often more than doubled compared to farmers that did not incorporate push-pull practices. In addition, push-pull farmers were also able to reduce their costs of labour and production.