A mealybug attacks a plant in Indonesia. Parasitic wasps have been deployed to combat the bug in some areas, with mixed results. Photograph: Georgina Smith/Ciat
Cassava, which is originally from South America, is now south-east Asia’s third largest source of calories after rice and maize. An estimated 40 million people in the area depend on the plant for their livelihoods and the crop forms the basis of a $5bn (£3.5bn) regional market in starch, which is used to make products ranging from paper to biofuel.
But researchers say the crop’s viability is now at risk as more intense dry spells and rains bring about conditions in which pests and diseases can flourish.
Scientists who gathered data from more than 400 sites across the region found symptoms of witches’ broom disease or mealybug in at least two-thirds of the cassava fields they studied.
The former, which has already reached the Philippines, Vietnam, Cambodia, Laos and Thailand, causes leaves to discolour and bunch into a shape resembling a witch’s broomstick.
The latter, which menaced crops in Africa after it was accidentally introduced from South America in the 1970s, destroys yields by leeching essential nutrients from the plant. The bug is now moving into parts of Indonesia where cassava is central to food security.