With the Mekong delta province of Vinh Long failing to control witches' broom when it affected longan trees, the disease has now spread to the rambutan crop, causing farmers severe losses.

In recent years the disease, which causes an abnormal brush-like cluster of drafted, weak shoots arising from or near the same point on branches and affects fruiting, has infected large areas of longan in the delta.

Vinh Long was among the worst hit during the peak outbreaks between September 2011 and March 2012, with 9,000ha out of its 9,840ha of longan affected, according to the province's Department of Agriculture and Rural Development.

Nguyen Thi Anh, who has grown rambutan on 3,000sq.m in her 8,000sq.m orchard in Long Ho district's Hoa Ninh commune, said that three years ago the disease hit her longan trees and she had to cut them down and replace with rambutan.

This year the rambutan began to fruit but has been affected by the disease, she said.

All 60 rambutan trees in the 2,000sq.m orchard owned by Tran Anh Tuan in Hoa Ninh commune were severely affected by the disease during the flowering period this year.

The trees, which yielded fruits for the last two years, are unlikely to do so this year because the disease causes young rambutan fruits to fall.

"Would we have to cut down the infected rambutan trees like we did with infected longan trees since there is no effective treatment for the disease?" he asked.

More than 126ha out of the commune's 550ha of rambutan are diseased, Doan Ngoc Niem, an agricultural official in Hoa Ninh Commune, said.

Witches' broom is caused by a bacteria whose vector is nhen long nhung (Eriophyes dimocarpi), a tiny pest species that cannot be seen with the naked eye.

Authorities have warned farmers to apply measures to stop the disease from affecting rambutan, including cutting infected branches and using chemicals to kill nhen long nhung.

Nguyen Van Liem, deputy director of the Vinh Long province Department of Agriculture and Rural Development, said his department had instructed the Plant Protection Sub-department to take measures to treat and prevent the spread of the disease.

In the province, a large area of longan crop remained affected by the disease, which has the potential to spread to more rambutan trees, he said.

Therefore, preventive measures should be taken to control the disease in both cases, he said.-VNA