Scientists from the International Centre for Tropical Agriculture (CIAT) have warned of an imminent outbreak of highly damaging pests and diseases targeting cassava in areas currently considered safe havens.
A report entitled “Threats to Cassava Production: Known and Potential Geographic Distribution of Four Key Biotic Constraints”, just published in the journal Food Security, identifies hot spots around the cassava-producing world where conditions are right for outbreaks of some of the crop’s most formidable enemies: whitefly, green mite, cassava mosaic disease and cassava brown streak disease.
Cassava is the third-most important food crop in the tropics after rice and maize, consumed daily by up to one billion people, mostly in sub-Saharan Africa.
Cherished for its ability to thrive in harsh conditions, cassava produces its carbohydrate-rich roots in poor soils, even in times of drought. Industrial cassava production is also a crucial source of income for hundreds of thousands of smallholder famers.
By using a technique known as ecological niche modeling, CIAT scientists were able to conduct a detailed global risk assessment for cassava, in relation to the four pests and diseases. They compared cassava producing areas where they are already present, with areas that have similar environmental conditions, but where specific pest and disease pressure is either absent or low.
They found that the conditions are right for combined outbreaks of all four pests and diseases in some of the world’s major cassava producing zones. These include Africa’s Rift Valley region, much of Southeast Asia, southern India, Mato Grosso state in Brazil, and northern South America.
“The research shows that there are perfect niches for some highly damaging pests and diseases in areas currently considered safe havens,” explained CIAT entomologist and leading cassava expert Tony Bellotti, one of the article’s authors.
“An outbreak of one of these could be very severe, but all four at once would wreak havoc. Historically, cassava pests and diseases have demonstrated a remarkable ability to colonize new areas in new countries, if conditions are favorable,” he said.
“We’ve seen how quickly the cassava mealybug, another major cassava pest, became established for the first time in Thailand in 2008/9, crippling production. While the Thai authorities reacted quickly and decisively by deploying a parasitic wasp to attack and control the mealybugs, the outbreak still wiped out almost a third of last year’s harvest and cassava fields across Southeast Asia continue to be at risk.”
“We’re already getting reports of sightings of pests in new areas, which seem to support our findings,” he added.
A major cause of the rapid spread of cassava pests and diseases according to the study is the method by which the crop is propagated, with new plants grown from stakes – stem cuttings taken from older plants. As well as helping transfer infections from one generation of cassava crops to the next, the stakes are often transported very large distances – sometimes across international borders – enabling the spread of pests and diseases far beyond their geographic centers of origin.
“In an age of global travel, local risks to cassava production are now global risks – all it takes is one contaminated stake and a pest or disease could jump an entire continent and establish itself very quickly. In many places farmers are totally unprepared for this and if we’re going to protect one of the world’s most important crops, it’s going to be critical to refine and enforce establish protocols for the movement of stakes,” Bellotti added.
The authors recommend the more formal international early warning systems for cassava, to ensure a swift response to any outbreaks.
The study was funded by HarvestChoice, an initiative of the University of Minnesota and the International Food Policy Research Institute (IFPRI).