The yields in many citrus fruit and dragon fruit orchards in the Mekong Delta have fallen after they have been infected by new diseases.
Nguyen Van Tam’s 4,000-sq.m grapefruit orchard in Tien Giang province’s Cai Lay District has seen its output fall by one-third in the last harvest season compared to previous seasons because of the destruction caused by a worm, Citripestis sagittiferella, known locally as “nam hong”.
Tam says he has lost about 10 million VND (470 USD) from the yield decline.
About 405ha of Tien Giang’s 10,721ha of citrus fruits have been infected by the worm. The province’s Department of Agriculture and Rural Development estimates the infection rate at 10-20 percent of the trees in each orchard.
The worm, which penetrates citrus fruits and damages them, has been seen in the Delta provinces of Tien Giang, Vinh Long, Ben Tre, Hau Giang and Dong Thap only since 2011, according to the Southern Fruit Research Institute.
The institute has instructed farmers to apply several measures to protect their grapefruits, including using plastic to cover the fruit and painting the tree trunks white with lime.
Some orchard owners said they have also used nets with lights that attract insects, but they have not been able to catch the worm.
A new disease has also attacked dragon fruit orchards in Tien Giang, infecting young branches and fruits.
Le Van Minh in Cho Gao District’s Dang Hung Commune said 80 percent of his 2,000sq.m orchard were affected by the disease in the last harvest season.
Nguyen Van Sinh, head of the Tien Giang province’s Plant Protection Department, said the disease has been identified as the brown spot disease caused by the Neoscytalidium dimidiatum fungi.
The disease spreads rapidly, especially in the rainy season, and in orchards that maintain poor hygiene and use too much nitrogenous fertiliser and other chemicals to stimulate growth, he said.
The disease, which cannot be treated, has affected both the quality and yield of dragon fruit, he added.
In Long An province, about 967ha of 2,200ha of dragon fruit orchards have been infected by the disease.
The disease was first appeared in the southern central province of Binh Thuan, the country’s largest dragon fruit producer, in 2009.
Local officials have told farmers that they need to drain water from dragon fruit orchards, destroy disease-infected branches and fruits and use fertilisers properly to restrict the disease from spreading.
Besides the new diseases, many fruit orchards, including those growing milk apple, mango and sapodilla have suffered from a condition in which the roots of many trees rotted and the leaves and branches of others dried up.
Many orchard owners attributed it to fake fertiliser, while others blamed it on inclement weather, stagnant water and the soil losing nutrition because of the closed dyke systems built to control floods.
However, local officials say orchard owners applying techniques to force their trees to produce many fruits is the major reason for the damage.
Trinh Cong Minh, deputy director of Tien Giang province’s Department of Agriculture and Rural Development, said the price of milk apple and sapodilla was high in previous seasons and many orchard owners had applied techniques to make the trees to bear fruits during their off season.
“This has caused the weakness of fruit trees, causing many trees to die,” he said.
The department is working with the Ministry of Agriculture and Rural Development’s South Plant Protection Department to find measures to rescue the trees and orchards, he said.