21 Jan 2010
CIAT
Colombia, Sri Lanka - International Center for Tropical Agriculture CIAT scientists and their partners in Southeast Asia have issued urgent preliminary guidelines to tackle deadly pest and disease outbreaks that have crippled cassava production in parts of the region.
The move follows a CIAT investigation into reports from Thailand's eastern and northeastern regions, of damaged and stunted cassava plants with low root yields.
Cassava is an essential pro-poor crop in the region, where it is grown by around 5 million smallholders, mainly to supply the starch processing and animal feed industries. In Thailand alone, the industry is worth US$1.5 billion, and the country accounts for three-quarters of the world's cassava exports.
CIAT entomologist, Dr Tony Bellotti, was part of the investigation team that traveled from CIAT headquarters in Colombia to the region: "When we arrived at the plantations in Thailand, I was stunned. Straight away I realized we've got real problems."
A drive around the Korat region, about three hours from the capital, Bangkok, confirmed the worst: the road was flanked by field-after-field of affected plants.
One troubling discovery was the large number of mealybugs - well-known cassava pests in Latin America and Africa, but rarely a problem for cassava producers in SE Asia. The sap-sucking insects weaken plants, resulting in leaf distortion, and lower root yields.
The Thai fields were also found to be infested by tropical whitefly and red mites, while Cassava Bacterial Blight (CBB) and Brown Leaf Spot disease were also widespread. None of these pest and disease problems had previously caused significant losses in Thailand, but the severity of the current outbreak they has been attributed, in part, to higher than usual rainfall in the region, linked to climate change.
Some analysts now predict a cut in Thai cassava output by at least 30% this season; some farmers face losses as high as 80%. Many have already abandoned their crops.
Dr. Tin Maung Aye, a cassava specialist in CIAT's Asia office said: "These pests and diseases will place a huge strain on Thailand's cassava production. Not only will the incomes of smallholder farmers be greatly affected, but so will those of the many laborers employed in the cassava industry. There will be widespread economic and social implications."
Double-trouble
Then, more bad news as farmers in neighboring Vietnam began to report similar symptoms in their cassava crops. The team again found mealybugs, tropical whitefly and red mites, but the main problems were not pests, but diseases.
"The CBB was incredible," continued Tony Bellotti. "The disease was just oozing from the stems. I've worked with cassava for 35 years and I'd never seen anything like it."
They also found symptoms known as Witches' Broom, still new to Vietnamese farmers, typified by discoloration and distortion of cassava leaves, and reduced branching of the stems. When the affected cassava is uprooted, the roots are thinner and smaller, with rough-textured skins, and drastically reduced starch content.
Further investigations are underway, and CIAT is now investigating reports that fields in Cambodia, Laos and the Philippines have also been affected.
"It's no surprise if these problems are spreading quickly," said Bellotti. "If the mealybug, for example, can find its way from its native Latin America, across the Atlantic to Africa, and then to Asia, it can find its way around the Mekong region and beyond.
"We can be fairly sure that China and Myanmar will be hit soon, and in time, Indonesia too," he said.
"Cassava production in SE Asia has enjoyed an extended honeymoon period," he continued. "That period is now over."
Taking control
CIAT Asia is working with national partners to provide cassava management guidelines. "This is a red alert," said Tin Maung Aye. "We're still coming to terms with the scale of the problem, but without decisive action and donor support, we expect a huge slump in cassava output in SE Asia. That would be devastating for rural livelihoods in the region.
"The spread is almost certainly caused by the movement of infected planting material," Tin continued. "One of the first responses is for the authorities in affected countries to impose strict quarantine regulations on the movement of cassava, especially the stems used as planting material, and of related species, like jatropha.
"Farmers also need to be trained to select and safely store clean planting material, and to identify pests and diseases. Establishing an effective surveillance and monitoring system with a GIS database is essential.
"We will also need to develop an Integrated Pest and Disease Management (IPDM) strategy, based primarily on biological control. With the right support, the current attempts to develop an effective IPM strategy could be strengthened very quickly, which will help protect next season's crop. Over the medium to longer term, the biological control and IPDM strategy would be strengthened and include release of parasites to control pests and the insects that carry the diseases. Breeding of cassava varieties with greater pest and disease resistance would become a priority.
"As a result of generous, long-term support from the Nippon Foundation, CIAT has had a profoundly positive impact on cassava production in SE Asia, and the livelihoods of cassava farmers. We are therefore well-placed to provide solutions to the current pest and disease outbreaks," he continued. "But there is no time to lose."
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