Clamp-down launched on devastating threats to starch crop

3 December, 2013 by (comments)
A farmer in Laos checks his cassava harvest © Neil Palmer / CIAT

A farmer in Laos checks his cassava harvest is healthy © Neil Palmer / CIAT

Scientists are ramping up efforts to contain and clamp-down on serious pests and diseases threatening “devastating” impact on a leading food security, cash and bio-energy crop in Southeast Asia.

In the region, cassava is the third largest source of calories after rice and maize, and an important food crop, particularly in Indonesia. The crop supports an estimated 40 million people, and underpins a steadily growing local starch and biofuel industry. Last year in Vietnam alone, cassava exports were valued at USD 1.3 billion.

But rapidly emerging pests and diseases pose a significant threat to farmer’s yield and income. “It’s difficult to gauge the exact impact of these novel pests and diseases – though they cause considerable yield reductions and have spread rapidly through the Southeast Asia region,” said Dr. Kris Wyckhuys, lead entomologist in Asia for the International Center for Tropical Agriculture (CIAT).

“Our data suggests a devastating impact on cassava production,” he added. “It’s vital we act now to contain or control these major pests, diseases and threats to safeguard the livelihoods of countless Southeast Asian cassava growers.”

CIAT has launched a series of training courses in Colombia and Vietnam with national partners to bring together more than 70 researchers and top international experts to share information about rapid diagnostic tactics, diseases-free planting material, pest management techniques and ready-made curative technologies.

Pic by Neil Palmer (CIAT).

Whitefly infestation on a cassava leaf © Neil Palmer / CIAT

The golden days are over

Since its introduction from South America centuries ago, cassava in Southeast Asia has enjoyed a pest and disease-free past. But steady intrusions of mites, whiteflies, mealybugs and cassava-thwarting diseases are on the increase.

One of the most severe cassava pests globally is the cassava mealybug Phenacoccus manihoti, locally known as the pink mealybug. It wreaked untold havoc on cassava production across Africa in the 1980s, with record yield losses of up to 82% and unprecedented impacts on local food security.

In Africa, cassava mealybug is now largely under control, thanks to the parasitic wasp Anagyrus lopezi, a specialized natural enemy of the pest. Its introduction and continent-wide distribution is recognised as one of the most successful pest control programs in the world.

Yet in 2008, alarmed scientists discovered the pest in Thailand. The quick response by Thai authorities and partner institutions to swiftly release the parasitic wasp appears to have brought mealybug populations down over the years.

But the bug is still on the move – and threatens to engulf the entire region’s cassava growing plots. Already it has been detected in six of Vietnam’s key cassava-growing areas as well as Lao PDR, Cambodia, Myanmar and Indonesia.

Ngo Tien Dung, Deputy Director General of Vietnam’s Plant Protection Department, said: “Nationwide monitoring is needed to present us will the full picture of the distribution of these pests.”

Mealybug infestation on a cassava leaf © Neil Palmer

Mealybug infestation on a cassava leaf © Neil Palmer / CIAT

A bad spell on regional harvests

Among the most destructive of new infectious diseases is cassava witches’ broom. True to its name, it spreads leaves in the shape of a witches’ broom and spells disaster for farmers, resulting in up to 80 percent crop loss and 30 percent reductions in yield and starch content.

Prevention tactics are useless once the disease has struck – all farmers can do is burn their crop. “A farmer is doomed once his crop has cassava witches’ broom,” said CIAT molecular biologist Manabu Ishitani, leading training sessions in Vietnam. “The only option is crop elimination.”

As cassava is vegetatively propagated, stakes cut from infected plants will fuel the spread of pests and diseases. Quarantine measures to restrict the movement of infected plants are crucial – it remains to be seen whether national quarantine systems are sufficiently robust.

In the meantime: “It’s vital for us to develop clean stake systems for each country, so that clean cassava tissue can be multiplied and certified disease-free, for transfer to farmers in the field,” said Ishitani.


Training course at the CIAT Headquarters in Colombia © Julio Cesar Martinez / CIAT


The jury is out on what is causing the influx. Researchers say that although climate change is often blamed, movement via trade is a much bigger driver. Yet the fact that mealybug and cassava witches’ broom among other pests and diseases have arrived in Southeast Asia – and inflicted significant damage – only bolsters the likelihood that others are on the way, they warn.

Dr. Nguyen Anh Vu from Vietnam’s Agricultural Genetics Institute, attending training on management of cassava witches’ broom disease at CIAT’s headquarters in Colombia, said: “What I and my colleagues have learned will significantly increase our detection and management capability. We aim to make cassava witches’ broom a thing of the past.”

Deputy Director at Vietnam’s Plant Protection Research Institute, Dr. Trinh Xuan Hoat, said current training courses are critical to equip regional research communities with new knowledge on cassava threats and diagnosis of pest disease management techniques.

“We consider cassava pests and diseases a new and severe problem for the region, not for any particular country,” he said. “Broad thinking is therefore needed and cross-border research cooperation is crucial to address these emerging threats.”

Training courses were supported by the International Fund for Agricultural Development (IFAD) and the Colombian Presidential Agency for International Cooperation (APC).

For more information contact: g.smith[at]

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