Agriculture officials blame poor management of plants by growers for outbreak

Tshering Palden

A farmer in Martshala gewog, Samdrupjongkhar, Sonam Yeshey, cut down 19 orange trees after they were detected with citrus greening.

He feared how much of his over 1,000 mandarin trees he would lose. “I never heard of a disease like that, but had to cut down those dying orange trees, as I feared the disease would spread to the rest of the other trees,” Sonam Yeshey said.

His two neighbours, whose orange trees had the same symptoms, refused to fell the infected trees, despite the gewog agriculture officer’s repeated recommendations.

This, agriculture officials said, was one of the main problems in dealing with pest control, after its first detection in Punakha and Wangduephodrang in 2001.

Sonam Yeshey said village elders believe the infected trees would regenerate after some years.

“Agriculture officials feel otherwise,” he said. “Which is true?”

The disease is caused by a bacterium (Candidatus liberi- bacter asiaticus) and spread by an insect, a psyllid called Diphorina Citri, which is easily transmitted to other trees if the host is not removed.

Deputy chief plant protection officer Namgay Om said there was no cure for the dis-ease.

“We have to terminate the source of the infection, by cutting down infected trees, and spraying insecticides, to control the pests thereafter,” she said.

Her office, National Plant Protection Centre at Semtokha, Thimphu, carries out sample collection, detects plant dis- eases and provides technical support.

In 2006, a testing laboratory for the samples was established, but the human resource shortage persists.

Of the 16 mandarin-growing dzongkhags, the disease had been detected in 12 as of 2010.

“It doesn’t mean that all orchards in the respective dzongkhags are infected,” Namgay Om said. “It shows that the samples collected from these dzongkhags have tested positive.”

Tsheten Dorji from Nanong under Pemagatshel has over 40 orange trees infected in his or- chard of over 150.

“I sprayed insecticides or cared for the trees by watering and clearing the bushes around them, only after the trees were infected,” he said. “No one had told me about the disease until I learnt that the orchard had been attacked.”

Agriculture officials said they carry out awareness campaigns though fairs, and extensions officials and that they have a full program under the ministry solely to address citrus issues.

Surveys and sample collections are also carried out annually to detect the presence of the disease.

Agriculture department director Chencho Norbu said Bhutanese orange orchards in general lacked management.

“We need to give back to the soil what is used through the harvests,” he said. “Lack of nutrient deficiency also makes the crop susceptible to diseases.”

He said the movement of saplings was restricted, except for those from government nurseries.

“We discourage private nurseries in developing saplings and provide those, who would make an orchard, with specially cultivated saplings,” he said.

There are about four nurseries.

The department carried out a mass awareness campaign in 2004 on the disease distributing sprayers and insecticides for pest management.

Mandarin production ranks with potato as the two major ex-port crops of Bhutan.

“However, farmers pay no attention to pruning and crop management, so that the national average is the second lowest in the region,” the director said.

Citrus is the highest-value export crop for Bhutan.

Mandarin cultivation in Bhutan is categorised into Sikkim mandarin (found in south-west dzongkhags) and Khasi mandarin (found in south-central and south-east dzongkhags).

About the disease:

The disease was first reported in China as early as 1890s.
Huan Long Bing (HLB), known as citrus greening, has the following symptoms: stunt- ing, twig dieback, sparse yellow foliage, severe fruit drop, severe decline seen mainly with Asian greening which is the kind of disease spread in Bhutan.

Why the name Greening? The fruits of the infected trees do not have proper colour, remaining green on the shaded side (the part of the fruit that does not face the sun) hence the name greening. The shoots of the infected trees are yellow, hence the Chinese name ‘Huang-lung-pin’ or yellow shoot.