Vietnam: Disease strikes Delta longan crop

Witches' broom disease is sweeping through more than 60 per cent of the longan-growing area in the Cuu Long (Mekong) Delta, leaving many farmers with severe losses, according to the Plant Protection Department.

Can Tho City and Soc Trang, Tien Giang, Tra Vinh, Vinh Long, Dong Thap, and Hau Giang provinces have all announced epidemics, with 24,000 ha out of their 39,000ha under the fruit being affected.

"Witches' broom, which causes an abnormal brush-like cluster of shoots arising from or near the same point on branches, affecting fruiting, is caused by a bacteria," said Dr Nguyen Van Hoa of the Southern Fruit Research Institute.

The vector of the bacteria is nhen long nhung (Eriophyes dimocarpi), an insect that is 0.12-0.17mm long and cannot be seen with the bare eye, Hoa said.

The disease appeared in Viet Nam in 2003 from infected longan strains imported from neighbouring countries, according to experts.

There are no effective measures to prevent or control the disease.

Nguyen Minh Hai of Tien Giang Province's Chau Thanh District said 85 per cent of the 130 longan trees in his 0.4ha orchard were affected.

"I have to cut down all the infected trees and spray disinfectants to prevent the disease from spreading," the farmer, whose trees are more than 10 years old, said.

Support

Nguyen Van Liem, deputy director of the Vinh Long Province Department of Agriculture and Rural Development, said since the disease outbreak occurred, his department has been actively taking measures across the province to contain it.

Vinh Long is the worst affected in the delta with 9,020ha out of its 9,840ha affected by 30-100 per cent, according to its Department of Agriculture and Rural Development.

"The department has also studied growing other fruits such as green-peel grapefruit, king orange, and Nam Roi grapefruit in severely affected areas," Liem said.

It has also organised training courses for 2,010 farmers on measures to control witches' broom this year.

The measures include trimming branches after harvest to remove infected parts, providing adequate water and proper fertilisers for longan trees, and not planting infected saplings.

The Tra Vinh Province People's Committee has earmarked VND12 billion (US$570,000) to help control the disease.

The money will be used to survey infected areas, organise disease-prevention courses for affected farmers, and give them financial support.

Cau Ke District accounts for well over half of the province's 3,000ha of longan. In its Hoa Tan, An Phu Tan, Ninh Thoi, and Tam Ngai communes, all 1,700ha have been affected by witches' broom, reducing fruit output by more than 60 per cent.

Many farmers have suffered losses and are in debt, according to agriculture departments in the region.

In April the Government decided to provide farmers assistance worth VND7 million per ha if more than 70 per cent of their longan orchards are affected by the disease and VND5 million if it is 30-70 per cent.

The subsidy is meant to enable farmers cut down diseased trees and buy chemicals to kill nhen long nhung.