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Rice pests multiply post-floods

Damage from the brown planthopper, a rice-devouring pest, is evident in this central plains rice field
(Sylvia Villareal/IRRI)

Heavy flooding across parts of Thailand in 2011 has fuelled outbreaks of a rice pest that can decimate harvests, experts say.

The pest, known as brown planthopper (BPH), transmits two viruses that hit yields as well as eating away at rice plants.

"The floods have certainly made things worse," Kong Luen Heong, principal scientist for the Manila-based International Rice Research Institute (IRRI) told IRIN.

"Moreover, they will impact [on] upcoming harvests as well."

"BPH is attacking the rice bowl of the country for the eighth time in a row [over the past four years]," said Kukiat Soitong, from the Thai government's Rice Department, based in the Agriculture Ministry, adding that "150,000 hectares have already been seriously damaged in the central plains, in the basin of Chao Phraya river".

Affected provinces lost 30 percent of their rice production due to BPH in early 2010, amounting to around 1.3 million tons for the country, or more than 15 percent of the nationwide harvest, which takes place twice a year, reported the Rice Department.

According to the Thai Rice Exporters' Association, Thailand produces 4-5 percent of the world's rice, and is the largest exporter, with 10.8 million tons in 2011.

Last year's flooding, which affected more than two million people across 28 provinces and damaged more than two million hectares of farmland, worsened the longstanding pest problem by drowning natural enemies of BPH, including insect parasites and spiders.

"Because of the floods and the killing of BPH's natural enemies, farmers are more dependent on insecticides for several seasons. And the fact is that using insecticides makes BPH even stronger," added Kukiat.

Most insecticides kill BPH's natural enemies, rather than BPH itself. The brown planthopper has an "unmatched" capacity to become resistant to any molecule used against it, according to Keng Hong Tan, a retired entomology professor based in Malaysia.

He says the pest has even developed resistance to one of its own hormones when applied as a control measure.

And while IRRI and Thailand's Rice Department launched a campaign in July 2011 to ban the two insecticides most often used in rice cultivation, cypermethrin and abamectin - known to cause BPH's resurgence - the ban is unlikely to have a significant impact.

"This campaign will have limited immediate effects because of the floods," said Heong. "It will take some strong will to break the vicious circle that helps BPH."

Yet banning insecticides is the only way to control BPH outbreaks in the long term, said Ho Van Chien, director of the Vietnamese government's plant protection centre for southern Vietnam.

According to IRRI, BPH damaged hundreds of thousands of hectares across Asia, leading to hundreds of millions of dollars in lost production.

Since 2009, Bangladesh, Cambodia, China, India, Indonesia, Japan, Malaysia, Myanmar, the Philippines, Thailand and Vietnam have been severely affected at least once.

"BPH puts the whole rice ecosystem in jeopardy," said Erma Budiyanto, director of plant protection in Indonesia's Ministry of Agriculture.

"There could be a humanitarian situation because of this pest in the future if insecticides remain as widely used as today," said Heong.


This article was produced by IRIN News while it was part of the United Nations Office for the Coordination of Humanitarian Affairs. Please send queries on copyright or liability to the UN. For more information:

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