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Letting nature manage its battles

Planting different types of flowering plants alongside rice can help encourage predators and parasitoids that prey on pests (© IRRI/KL Heong)
Planting different types of flowering plants alongside rice can help encourage predators and parasitoids that prey on pests
© IRRI/KL Heong

Advice for managing rice pests, such as planthoppers, has taken on a simple message: let nature have its way in your fields. In essence, leave alone the 'friendlies' such as spiders, predatory bugs, and parasitic wasps, and you will increase your crop's chances against planthopper outbreaks. But as straightforward as the message is, doing away with time-old practices dependent on assurance from insecticides is not.

In a statement calling for support on pesticide regulation and for a ban of the use of specific insecticides in rice that contribute to planthopper outbreaks, the International Rice Research Institute (IRRI) has offered alternative practices to better manage pests, and has called on its partners to join its concerted efforts to change mind-sets.

Asia bears hopper brunt

The message comes as rice losses from planthopper outbreaks spread across Asia. In 2010, the pest destroyed more than 25,000 hectares of rice in Indonesia and about 1.1 million tons of paddy rice with an export potential of US$275 million were lost in Thailand. In 2009, an estimated 300,000 hectares were heavily infested in China and Vietnam, of which more than 6,500 hectares suffered complete crop failure.

The hopper problem, which persisted in Vietnam from 2005 to 2007, prompted the country to suspend rice exports in 2007, to protect the domestic supply. However, this caused volatility in rice prices globally, prompting warnings from the World Bank that millions would be pushed further down the poverty line.

Ecosystem breakdown

Planthopper outbreaks are primarily caused by a breakdown of biological control functions in the rice landscape, what is known as 'ecosystem resilience'. IRRI entomologist Dr KL Heong points out that a rice field, left on its own without interference from chemicals, has its own 'foot soldiers' that provide protection from pest outbreaks.

Spiders help increase crop's chances against planthopper outbreaks (© IRRI/KL Heong)
Spiders help increase crop's chances against planthopper outbreaks
© IRRI/KL Heong

A rice field is a patchwork of rich diversity in which spiders, aquatic bugs, parasitic wasps, and predatory bugs thrive. An irrigated rice ecosystem in the Philippines, for example, is home to nearly 700 organisms, most of which are natural enemies of the pest and friendly to rice. Each has a role in a delicate balance of inter-relationships, making the landscape environmentally sustainable.

"Biodiversity is about balancing the positives and the negatives," says Dr Heong. "It is about roles, interactions, and stability. Without natural enemies, planthoppers multiply and can overrun a rice field, causing an outbreak." Natural enemies keep the pest population in check but the whole system starts to fall off-balance the moment chemicals are applied. However, no amount of solid, environmentally sustainable practice will work unless farmers are weaned from the belief that they need to use chemicals to control pests.

Yet, pesticides are marketed as consumer goods, using emotional appeals and even giveaways, effectively putting reason on the back burner. Dr Heong believes that pesticide use must be knowledge-based in order to preserve the natural balance in the rice ecosystem and so prevent outbreaks.

A crucial step against chemicals

Following reports of damage in 11 provinces in Thailand, which affected 104,000 hectares, the country's Minister of Agriculture and Cooperatives, Theera Wongsamut, announced a US$12.8 million initiative to stop the use of two outbreak-causing insecticides - cypermethrin and abamectin - in Thai rice crops. IRRI director general Dr Robert Zeigler applauded this action. "It is of international significance that Thailand should undertake this initiative because, as the world's largest exporter of rice, it is recognized as a global leader in the rice industry," he said.

In its action plan to solve the hopper problem sustainably, IRRI has proposed the restoration of biodiversity in rice fields, as well as building ecological resilience. Specifically, IRRI recommends ecological engineering approaches that introduce landscape elements such as flowers and other plants to promote buildup and to sustain a healthy population of natural enemies of planthoppers.

Regulating the marketing and use of pesticides will help farmers manage pests more effectively (© IRRI/KL Heong)
Regulating the marketing and use of pesticides will help farmers manage pests more effectively
© IRRI/KL Heong

IRRI also recommends the use of resistant varieties, or a combination of varieties, that are tolerant of the local or invading planthopper populations. However, to prevent the hoppers from developing resistance, farmers are advised against using the same variety for more than two years. Synchronous planting and fallow periods of one month in between successive crops of rice, as well as crop diversification schemes, are also included in IRRI recommendations.

To support farmers in their new approach, IRRI is calling on its partners in national governments and the private sector to regulate the marketing and improve the use of insecticides. The call is to change the classification of pesticides as consumer goods to being regulated materials, and to ban or restrict the use in rice of broad-spectrum pesticides that contain active ingredients known to contribute to planthopper outbreaks, including cypermethrin, deltamethrin, abamectin, and chlorpyrifos.

Certifying and training pesticide retailers is also recommended to prevent sales of fake, banned, or unapproved products, and to foster the promotion of integrated pest management and proper pesticide use.

Date published: January 2012


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