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An approach that combines sustainability and biological control principles is the ‘push-pull’ system, or ‘stimulo-deterrent diversionary’ strategy. Pioneered by Professor John Pickett of Rothamsted Research and Dr Zeyaur Khan of African Insect Science for Food and Health (ICIPE), the push-pull system uses intercropping, that is planting another crop between rows of the main crop, maize in this instance.

Pickett worked in the department responsible for inventing the new pyrethroid insecticides. “We’d seen criticism because they worked on neurotoxic action, and because they are very unstable and volatile and disappear, so we wanted to look at a non-toxic action. The idea was to produce control with plant chemistry by getting the plant to do it.”

The intercrop diverts (pushes) the pests from the main crop and entices (pull) them into a small trap crop and, at same time, brings in beneficial organisms such as parasitoids and predators. The research was published in prestigious science journal Nature. “Proving that you can do top science relevant to subsistence farming,” says Pickett.

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The push-pull system explained (click for enlarged version)

The system has been successfully used in more than 20,000 farms in Kenya and the practise has spread to Ethiopia, Tanzania and Uganda where it can help bridge the gap between subsistence farming and producing a saleable surplus.

Pickett says for the first time it provided technology suitable for subsistence farming. “Although there’s a lot of socioeconomists in the area there’s a misunderstanding of what these farmers are,” says Pickett. “People think they are like our farmers but not very efficient, and so they should move on by buying hybrid seed, fertiliser, pesticides, but you are talking to what is in economic terms a peasant farmer – they don’t buy things because they don’t sell.”

As well as enabling subsistence farmers to develop a surplus – sustainably, and without expensive, high-energy inputs – the push-pull system resulted in some serendipitous findings.

At the request of the local farmers, who wanted to grow some beans for cattle fodders as an intercrop, scientists discovered that using silverleaf (Desmodium) as an intercrop reduced the incidence of Striga, the African Witchweed, a serious weed problem throughout Africa.

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Push-pull has been widely adopted in eastern Africa. Image: ICIPE (click for enlarged version)

In turn, Pickett and colleagues learnt from the farmers that you could propagate Desmodium vegetatively – something not considered possible.  “If it hadn’t been for them trying to propagate Desmodium vegetatively, we wouldn’t know you could do that as well.” 

Pickett says local farmers do the push-pull really very well. “You can see where it is being practised from a distance because maize is head and shoulders above the rest.”

The work was part-funded and supported by Rothamsted International, which was formed in 1993 to use science to benefit the poorer farmers in developing countries.