Hevea Problems In Southeast Vietnam: The Weather and the Disease Factor

Geography:

In general, Vietnam’s terrain facilitates not only agricultural, industrial and urban development but also transport systems and their construction. The West and South-West, bordering the Mekong Delta, have the greatest potential for agriculture, in effect the country’s granary.

Within the country’s southern climatic region, the South-eastern part features an equatorial or tropical climate with high temperatures, almost unchanged throughout the year. The annual monsoon, however, makes for a defined seasonal distribution or precipitation, average annual rainfall at about 1,500 – 2,000 mm.

Agricultural land dominates the region. About 27% of the land area is allocated for agricultural purposes, there being twelve groups of land made up of three essential soil groups: reddish brown on basalt, yellow-brown on basalt and grey silt. These groups are extensive and of good quality, making them favourable for many kinds of crops such as coffee, cashew, peanut, sugarcane, food crops and especially rubber. Due to its nature, the rubber tree develops best at 22-27 °C, with rainfall of 1,500 – 2,500 mm/year. The area is suitable because of its basaltic soil and its terrain being favourable for people to move about. . With a sufficient labour force, experienced in planting, caring for and exploiting rubber latex, there are many rubber processing factories in Tay Ninh, Binh Duong and Binh Phuoc, which is why most of the rubber plantations are concentrated in the South East. There are significant difficulties in the development of rubber trees and the price of their product, however, in the form of storms, flooding, unusual weather and, most worryingly, disease in the crop itself.

Weather:

The South has only two seasons, dry and wet, each of them lasting about six months. The rainy season starts in May and lasts through the end of October. The dry summer starts in November and lasts to the end of April. Every year, Vietnam will suffer 12 to 14 tropical cyclones and tropical depressions. In 1964, there were 16 storms, already more than the average of previous years. 2013 was considered as the record year for the number of storms created by tropical low pressure in the East Sea, with 17 storms and four tropical depressions. 2017 repeated that record with exactly the same number of storms and tropical depressions. According to the Hydrological Forecast Centre, the number of storms and tropical storms operating in the South China Sea and directly impacting Vietnam in 2018 is likely to be comparable to the average of many previous years. Specifically, there will be about four to six of these directly affecting the mainland.

At the beginning of the season, typhoons and tropical cyclones tend to occur in the northern part of the South China Sea, which will then transfer to the south of the South China Sea in the final months of 2018. The typhoon season began early under the impact of La Nina in the first half of 2018. In the early months, regular and tropical storms affected the Central Region. From now to the end of the year there will be about eight to ten storms, created by the tropical low pressure in the South China Sea, four or five of them directly impacting land areas, with typhoons likely to be stronger towards the end of the season. By the end of the year, however, the impact of tropical cyclones and typhoons on the southern coast will not have been as substantial as in 2017. Due to seasonal factors, however, it is likely that un-seasonally heavy rain with thunderstorms and hail will appear, densely, over the whole country, especially in the Central Highlands and Southern Vietnam.

But now to the crux of the matter, a cautionary one already explored elsewhere and in detail by my colleagues in Indonesia and highlighted in a recent post from our CEO, Mr. Meyer: 

Typical Diseases:

White Powdery Mildew
The causative agent is Oidium Heveae Steinm. The disease is common in the period when rubber trees produce new leaves from January to March every year, especially when the temperature is down to 23 – 25ºC and the ambience foggy or misty. Diseases harm rubber trees of all ages from garden, through the nursery, to the rubber plantation. Areas with elevations above 300m suffer more severely due to low temperatures and frequent fogs. At present, the white powder frequently causes damage to the rubber plantations from the Southeast to the Central Highlands and extending to the Central region, significantly reducing production for the rubber plantations. Symptoms are leaves turning brown or light green. Young, infected leaves will fall off in large numbers. If leaves are slightly infected or infected at a later stage, they won’t fall, but there will be lesions with various types of brown patches on the leaf blade. After a fungal infection of seven to ten days, multiple spores form on the spot with white powder on both sides of the leaves. The stems also fall. If the leaves do not fall, the entire blade is deformed and turns first yellow, then deciduous. This results in reduced growth and yield, due to a gradual loss of the photosynthetic area and nutrient concentration to regenerate the leaf layers.

Leaf Rot
The diseases Phytophthora Botryosa Chee and Phytophthora Palmivora occur during the rainy season causing old leaves and fruit to rot. The petiole exhibits a white pus, the affected rubber becomes rotten and the fungus kills both new plants and seedlings. The diseases also spread to the tapped area of the trunk, so when the trees are 50% defoliated, it reduces the rate of latex flow (yield), including that during the wintering season.

Anthrax (Anthracnose) Fungus
A common disease causing significant harm during the rainy season. Fungal diseases are harmful to young plant parts, their leaves and shoots; a severe outbreak of the disease can lead to dry leaves, leaf fall, dying buds and dead tops.

An urgent solution is needed.

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Brandon Pham Cong Danh
General Manager, Representative Office in Vietnam