Originally published on September 6, 2013

Swollen shoot disease is pushing deep into Ivory Coast's primary cocoa-growing regions despite government efforts to combat it and could hurt output from the world's top grower over the long term, Reuters reported.

The news agency reported that, in the decade since it struck the centre-west growing regions, the disease has spread to 12 percent of all Ivorian cocoa farms, the government says. For now, experts say the impact on output is being masked by production from new plantations.

"It's progressing without a doubt," said Francois Ruf, an economist with French agricultural research centre CIRAD.

"It's already been devastating around Gagnoa, Guitry, Fresco and outside the Tai national park as well," he said, describing an area that straddles some of Ivory Coast's most productive cocoa farmland in the southwest.

The viral disease, first identified in neighbouring Ghana in the 1930s, causes a drastic reduction in yields in the first season following infection and then typically kills trees within a few years.

When it emerged in the centre-west region, the disease soon killed off 8,600 hectares of cocoa in Sinfra and Bouafle, leading to a 66 percent drop in output there, Ivorian authorities said.

It has since also been found near Issia, in the Daloa region that accounts for a quarter of the Ivorian crop, according to the cocoa marketing board, CCC.

Farmers said the disease was also gaining ground in the east along the border with Ghana, an area known for producing high-quality cocoa.

"We started seeing it two years ago. In the beginning, I didn't know what it was," said Noudoun Silue, who farms eight hectares near the western town of Duekoue. "We had to cut down the sick trees so the others wouldn't be contaminated."

The CCC in 2008 started a project to map the affected zones, which is still unfinished. Its preliminary surveys show the disease has affected 12 percent of cocoa farms across Ivory Coast, the governmen