The farming technique known as push-pull — which involves planting grasses with special properties to protect crops — started out as a rudimentary defense against stem borer insects. But it just keeps getting more sophisticated. It has evolved to fight off parasitic weeds, while also providing animal fodder and fertilizing the soil. Now, in a paper published this month, scientists have described ways to use it in areas without regular rainfall or irrigation.
The story of push-pull starts 22 years ago, when entomologist Zeyaur Khan arrived at the International Centre of Insect Physiology and Ecology station in Mbita, Kenya, with an assignment to find a way to ward off the stem borers that were plaguing corn fields in eastern Africa. When he began studying the stem borers’ lifecycle, he began finding grasses that had evolved with these insects. There were some grasses that the stem borers loved to eat — five times more than they loved the corn. There were other plants that had evolved chemical defenses against the bugs — some by repelling them, and others by attracting wasps that ate them.
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