Thứ Hai, 18 tháng 9, 2017

Cassava and Vietnam: Now and Then


Hoàng Kim

First, we can show some pictures is the latest record of cassava cultivation on four months after planting in the field in Phu Yen in August 2017. Then, we can learn from Dr. Claude M. Fauquest, Dr. Reinhardt Howeler and Professor Kazuo Kawano, the leading experts on international cassava, commented on cassava in Vietnam. Finally, we can read on the subject "Cassava conservation and sustainable development in Vietnam: an overview and direction"; “Achievements of research and development of cassava in Vietnam of 1975-2017"; "Cassava conservation and sustainable development in Vietnam: a key study in DakLak province in Central Highland"; "Cassava conservation and sustainable development in Vietnam: a key study in Phu Yen province in South Central Coast".

We learn more questions on cassava and root crops and tell them where to learn more…

On 21 -25 August, 2017, Dr. Claude M. Fauquet, Director of the Global Cassava Partnership for the 21st Century (GCP21), who cassava trip in Vietnam, do a road trip for five days to visit four key provinces and city Dong Nai, Ho Chi Minh city, DakLak, and Phu Yen. We look at cassava research and production and processing and shared meeting with presentations and discussions on collaboration between GCP21, CIAT and IAS, NLU for the ‘Cassava Conservation and Sustainable Development in Vietnam’.

"I have learned a great deal about cassava in Vietnam and I have a better view of what the near future will be in your country! The road from Daklak to Phu Yen was indeed very interesting and the cassava plantations are quite impressive. I was also quite interested to see the decline in cassava plantations with the competition with sugarcane and pepper, that is quite a concern! And the future will tell us what will happen. And thanks for organizing the visit to the village with the vice-king of cassava and his colleagues, very interesting and very enthusiastic lunch! I hope that his example will teach other farmers to adopt new varieties and that you can help in the process". Dr. Claude said.

After cassa trip in Vietnam. Dr. Claude send email to Dr. Hoang Kim and VNCP group:

"Hoang, I am coming to you, because you know everything in Vietnam and therefore you can probably advise on the next phase.
In our exchange of information prior to my visit, I said that the outcome of such visit was mostly unpredictable, and I believe now that the outcome could be to set-up a regional task force to control CMD in the region!
The following points are clear to me:
1.   The disease is now spreading quickly; mid 2016 the infection was located in a few places in Cambodia and now it is in 5 provinces in East Cambodia and at least one in Vietnam.
2.   The disease is mostly spread by cuttings, although whiteflies are present they play for now a minor, but important role.
3.   There are several initiatives that have been taken; JIICA, CIAT, FAO, ACIAR, but none at the level required to control the disease.
4.   We need to set-up a regional project simply because viruses do not know about borders and there is a lot of traffic of cuttings, at least Cambodia-Vietnam.
5.   Thailand, Laos, Cambodia and Vietnam should all be enrolled in the plan.
6.   GCP21 could serve as a catalyzer to promote the development of this regional plan.
I have contacted all parties, including Thailand (TTDI and KU), waiting for more comments. So far the idea is shared by many people.
My question to you are:
·     Do you share my views about the necessity of the regional plan?
·     Who are the very key Vietnamese institutions and persons in Vietnam who should be involved in the preparation of such plan.
·     Is there anybody in charge of CMD in Vietnam to collect and centralize samples, information…
Many thanks

Claude M. Fauquet,
Director of the Global Cassava Partnership for the 21st Century (GCP21)

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from research to practice
Reinhardt Howeler và Tin Maung Aye, 2015.



Like other crops, cassava can suffer from serious pest and disease problems that reduce yields. But being a long-season crop that is exposed to these problems over a long period, it is hardly ever economic, nor effective, to control these problems through frequent applications of pesticides. Most pests and diseases can be kept under sufficient control through integrated pest and disease management (IPM). This may include the following:

·         Plant cassava varieties with tolerance or resistance to the most important diseases and pests
·         Use high-quality planting material cut from mother plants that are free of pest and disease symptoms.
·         As an extra precaution, treat the stakes with a mixture of fungicides and insecticides before planting
·         Apply adequate amounts of fertilizers or manures to stimulate vigorous growth, which enhances resistance or tolerance
·         Do not apply insecticides to the crop as these may kill the natural biological control agents that will keep some major pests and diseases under control. Pesticides should only be used as short-term localized applications in “hot spots” where the pest is first observed, and only when the pest is in its early stage of development.  Pesticides can be used to control soil-borne pests, such as termites, as this will not affect the natural enemies of foliar pests
·         To reduce soil-borne diseases, mainly root rots, rotate cassava with other crops, especially cereals or grasses
·         Monitor the crop regularly and pull out plants with symptoms of disease or pest problems. Burn infected plant residues after harvest
·         Prevent the movement of diseased or pest-infested planting material from infested to non-infested fields
·         Do not purchase planting material from unknown sources, as pests and diseases may be a risk.

Major cassava pests

The most important pests found in all three continents include whiteflies, mealybugs, green and red mites, scale insects, white grubs, termites, and several pests attacking dried cassava during storage. Other important pests that are found only, or mainly, in Latin America include cassava hornworm, burrowing bugs, leaf-cutter ants, shoot flies, fruit flies, and lace bugs. Great care should be taken to not accidentally introduce these pests from Latin America to Africa or Asia, where they can cause tremendous damage due to the absence of their natural enemies. For that reason, it is absolutely prohibited to take vegetative planting material from one continent to another – as well as from one country to another. 
Some of the pests as well as certain diseases can also be accidentally introduced on other plant species, closely related to cassava, such as Jatropha curcas, used as fences in Asia and recently popularized for biofuel. Special care must be taken in the movement between countries of vegetative planting material of these related species, and that large Jatropha plantations are not located in cassava growing regions.


Whiteflies are considered one of the most damaging agricultural pests, both as a direct feeder and a virus vector; they are probably the most damaging pest on cassava in all three continents. The whitefly species Bemisia tabaci is the vector of several serious virus diseases in Africa, and the vector of the Indian and Sri Lankan cassava mosaic viruses found mainly in India. Another species, Aleurodicus dispersus or spiraling whitefly, is found in several countries in Asia and Africa, where it can cause serious feeding damage and possible yield losses.

White flies are one of the most serious cassava pests.

Whiteflies have six life stages – the egg, four nymphal stages, and the adult. The three types of damage they can cause are:
·         Direct damage – by piercing and sucking sap from the foliage, resulting in weakening and early wilting, yellowing, and necrosis of the lower cassava leaves
·         Indirect damage – by the accumulation of honeydew produced by the whiteflies, which serves as a substrate for the growth of black sooty mould on leaves, resulting in reduced photosynthesis 
·         As a virus vector – by the transmission of plant viruses from one plant or crop to another. Over 40 diseases of crops are transmitted by whiteflies worldwide. The yield losses in cassava can be as high as 76% if the plants are seriously affected.

To control high populations of whiteflies, many farmers spray insecticides, but this is ineffective as some whitefly species can double their population in only 4.2 days. They can only be controlled with very frequent applications – this is uneconomical and disrupts the natural biological control process. To control whiteflies effectively, integrated pest management (IPM) must be implemented, including:

·         Plant whitefly-resistant varieties
·         Enhance the function of natural enemies, among which are many species of parasitoids, predators, and entomopathogens. These techniques will be further developed in the future
·         Intercrop cassava with cowpea
·         Implement a “closed season” in which no cassava should be present in nearby fields in order to break the whitefly development cycle. This may not be as effective with whitefly species that have multiple hosts, such as Bemisia tabaci
·         Treat planting stakes by immersion for 7 to 10 minutes in a solution of 1 g of Thiamethoxam (Actara) per liter of water
·         Make foliar applications of Thiamethoxam at a high dose of 0.8 liter/ha or 0.6 liter/ha of Imidacloprid as a drench, but only on young plants (less than 6 months after planting) and when whitefly populations are still low.

Cassava stakes are treated in a solution of insecticides, fungicides, and micro-nutrients before planting.
Cassava mealybugs

Of the approximately 15 species of mealybugs attacking cassava plants, there are two species causing major damage to cassava in the Americas, i.e. Phenacoccus herreni and  Phenacoccus manihoti. The latter species was inadvertently introduced into Africa in the early 1970s, where it spread rapidly throughout the cassava growing regions of that continent. The same species was recently accidentally introduced into Thailand and within a year it had spread throughout the country and into neighboring Lao PDR and Cambodia, and later into Vietnam. It is now also reported in Indonesia.  

Several other species of mealybugs have been identified in Asia, including Phenacoccus gossypii, Phenacoccus grenadensis, and Phenacoccus jackbeardsleyi. Shortly after initiating feeding, the young nymphs produce a white waxy material which forms a cover over the insects. These mealybugs cause two types of damage to cassava: 

·         Mechanical or direct damage caused by their sucking-feeding habits, resulting in leaf yellowing and defoliation 
·         Indirect damage caused by the build-up of sooty mould on the leaf surface due to the mealybugs’ excrements, resulting in reduced leaf photosynthesis.

Phenacoccus herreni is found mainly in northern South America, while Phenacoccus manihoti was first found in Paraguay, Bolivia, and southern Brazil, where it was causing little damage due to effective biological control. However, once it found its way into Africa, and later into Asia, where its natural enemies were not present, it multiplied quickly and spread fast and far. Only after the introduction into Africa of several biological control agents, mainly parasitoids and predators from their area of origin in southern South America, was it possible to bring the mealybug population under control. From this experience, it was found that the parasitoid Anagyrus lopezi, a tiny wasp, was the most effective in attacking the Phenacoccus manihoti mealybug. When the females of the Anagyrus lopezi wasp lay their eggs in the mealybug, the developing larvae of the parasite will kill their host in the process. Thus, when the same species of mealybug also arrived in Asia, Thai researchers quickly introduced Anagyrus lopezi from Africa, learned how to mass-rear the wasp, and distributed millions of wasps into their cassava fields with excellent results. The Thais also taught farmers how to soak planting stakes in a solution of 4 g Thiamethoxam in 20 liters of water for ten minutes before planting. This treatment kills the mealybugs present on the stakes and prevents any mealybug from feeding on emerging leaves for at least one month after planting.
There are several species of mealybugs that can do serious damage to cassava plants.

For the effective control of mealybugs the following measures can be recommended:

·         Treat cassava stakes in a solution of Thiamethoxam at 0.5–1 g/liter before planting
·         Minimize the movement of planting material from infested to non-infested fields
·         Avoid spraying of chemical pesticides to conserve the population of natural enemies
·         Monitor the cassava fields every 2–4 weeks to detect the focal points of infestation (hot spots)
·         Remove the infested parts (apical buds) of the plants and burn these
·         Avoid the movement of planting material from one region to another.

Cassava mites
More than 40 species of mites have been reported feeding on cassava, of which the most important are the green mites, Mononychellus tanajoa and Mononychellus caribbeanae; and the red mites, Tetranychus cinnabarinus, Tetranychus kanzawai, and Tetranychus urticae. These can cause serious damage, especially in lowland areas with a prolonged dry season. The red spider mites, Tetranychus sp. are the most prevalent dry season pest in Asia. The most common species are Tetranychus urticae and Tetranychus kanzawai. However, the green mite has also been reported recently in Asia.

The cassava green mite prefers to feed on the underside of young leaves which become white-yellow and may be deformed and smaller in size. This may result in defoliation, starting at the top of the plant. Once the rains come, green mite populations are markedly reduced and cassava sprouts new leaves again.

Red mite populations may build up to high levels when favorable environmental conditions exist, especially in the dry season. Depending on plant age and the duration of attack, the yield losses can be between 20 to 50%. Red mites initially attack the mature leaves at the lower part of the cassava plant, before moving to the upper leaves. The first symptoms generally occur at the base of the leaf and along the midribs, seen as yellow dots along the main leaf vein, eventually spreading over the whole leaf, which turns reddish, brown, or rusty in color. Severely infested leaves dry and drop off, and plants may die.

Red mites (on the left) are a common cassava pest during the dry season in Asia, but the green mites (on the right) have now also been reported.
When confronted with heavy mite infestations in their cassava fields, many farmers start applying insecticides. However, this is not economic and may actually be counter-productive as even low doses of insecticides could kill the natural enemies before killing the mites. Mite damage is mainly controlled by the planting of resistant varieties. Further research is urgently needed to determine the most effective natural enemies of red spider mites, especially in Asia. But to be effective, moderate levels of host plant resistance should be combined with effective biological control. This is only possible as long as no chemical pesticides are used to control pests like whiteflies or mealybugs.

Over the past 30 years many surveys have been conducted in 14 countries of the Americas to collect and evaluate potential natural enemies of the green spider mite. Of these, 87 are collected species of phytoseiids – these are mites feeding on mites. These were found to have the greatest potential for controlling mites. Some of these phytoseiid species were shipped from Colombia and Brazil, via quarantine in England, to Africa in 1993, where at least three species from Brazil became established and were successful in controlling the cassava green mite population enough to reduce their damage to non-economic levels. Similar research should be conducted for the control of the red spider mite in Asia.

Current recommendations for the control of cassava mites include:

·         Plant resistant or tolerant varieties if available
·         Treat stakes before planting with Thiamethoxam in those areas where mites are a serious pest
·         Plant in the early wet season to enhance good establishment
·         Apply adequate and well-balanced fertilizers to improve plant vigor
·         Apply foliar sprays with water at high pressure to reduce mite populations
·         Apply only selective insecticides to protect natural enemy populations, as phytoseiid mite predators are very sensitive to even low dose applications of pesticides
·         Strictly enforce quarantine regulations.

Other pests that can be important locally include white grubs, scale insects, and termites. 

Major cassava diseases

Until recently, Asia had few serious pest and disease problems, but this is changing as production of the crop is intensified and cassava is planted throughout the year for industrial processing. The following are the most important cassava diseases in Asia:

Indian and Sri Lankan cassava mosaic disease

The Indian cassava mosaic virus (ICMV) and Sri Lankan cassava mosaic virus (SLCMV) are distinct begomoviruses, closely related to the virus that causes cassava mosaic disease (CMD) in Africa. There are several ICMV-tolerant cassava varieties, but many farmers in Kerala State of India prefer to plant their local varieties because of better eating quality. The recent introduction of lines resistant to CMD from CIAT, such as MNga-1 (developed by IITA in Nigeria) and other lines are now being used extensively in the Indian breeding program to produce ICMV-resistant varieties with other desirable characteristics.

Symptoms of Indian or Sri Lankan cassava mosaic disease.

Mosaic disease-resistant varieties (on the right) are now being developed in India.
The symptoms of these two diseases include chlorotic mottling of green leaves with leaf deformation, which may lead to leaf fall and severe stunting of plants. Leaves can also be reduced in size, twisted and deformed. Symptoms appear mainly during the wet season, making identification of diseased plants very difficult during the dry season. The disease is spread mainly through the use of infected planting material, as well as by the whitefly Bemisia tabaci. 

To effectively control the disease, the following practices are recommended:

·         Plant field-tolerant cassava varieties such as H-97, H-165, and Sree Visakham
·         Select disease-free meristem-derived planting materials, followed by clonal multiplication with periodic screening and pulling out of newly infected plants
·         Select disease-free planting material before the beginning of the hot dry season
·         Multiply disease-free planting material on a large scale at higher altitudes, where whitefly populations are very low or non-existent
·         Plant stakes first in a nursery at close spacing before transplanting only plants without disease symptoms to the field to prevent the spread of the disease
·         Follow strict phytosanitary practices, such as timely harvesting, prompt destruction of crop residues and pulling out of self-sown plants and weeds that may harbor both the disease and its vector
·         Cultural practices such as intercropping or a change of planting dates should be further investigated to determine their effectiveness.

Cassava bacterial blight (CBB)
This disease is wide-spread and can be serious during the rainy season. It is caused by the bacteria Xanthomonas axonopodis pv. manihotis.  Symptoms of the disease are the presence of water-soaked, angular spots and necrosis of leaves. The branches may partially or totally wilt and gum exudates may appear on the main stem or immature branches. There may be stem die-back and necrosis of some vascular strands of the stems and roots. The degree of plant damage varies depending on the degree of tolerance of the varieties and the growth stages of the plant.
Cassava bacterial blight (CBB) is one of the most common cassava diseases, 
but high-yielding varieties with good CBB tolerance are now available.
The disease is transmitted mainly through the use of infected planting material, or the use of infested tools. The disease can also spread from one plant to another by rainfall splash, and by the movement of people, machines, or animals from infected fields to healthy fields.  Fortunately, many high-yielding varieties with good tolerance to CBB are now available.  Other measures to control the disease are:

·         Use only healthy planting material from disease-free crops or plants derived from meristem culture, or rooted buds or shoots
·         Treat stakes by immersion for 10 minutes in a solution of cupric fungicides such as copper oxychloride or Orthocide at 3–6 g/liter; or immersion in hot water (49 °C) for 49 minutes. This treatment does not seriously affect sprouting
·         Plant at the end of rainy periods
·         Sterilize tools in hot water or in a dilute solution of sodium hypochlorite after their use in CBB-infected plots
·         Apply fertilizers, especially potassium
·         Pull out and burn any diseased plants and infected crop residues
·         Intercrop cassava with other species to reduce plant-to-plant dissemination of CBB by rainfall splash; fast growing crops like maize will also reduce dissemination by wind
·         Rotate cassava with other crops or leave the field in fallow for at least six months between cassava crops to prevent the carry-over of the disease in the soil.

Cassava root rots

This disease complex is widespread in all three continents, but is found mainly in heavy, poorly drained soils with high organic matter content, and during intense rainy periods. The disease can be caused by a wide range of fungal or bacterial pathogens that attack woody plants such as cassava, and cause root deterioration, either as the crop grows or after harvest when roots are stored.

The most common root rots are caused by a variety of species within the genus Phytophthora, especially Phytophthora drechsleri. The disease can attack both young and mature plants, causing sudden wilting, severe defoliation, and soft root rot. The infected roots exude a pungent, watery liquid, and they decompose completely.

Root rots are commonly found in heavy or compacted soil and in areas with heavy rainfall
The disease is best controlled by planting resistant varieties in combination with practices such as:

·         Plant preferably on light-textured, moderately deep soils with good internal drainage
·         If necessary, improve drainage by the use of a subsoiler
·         If the soil is rather clayey and flat, plant on top of ridges
·         Rotate cassava with cereals or grasses when more than 3% of plants show symptoms of root rot
·         Eradicate diseased plants by removing infected roots from the field and burning them
·         Select healthy planting material from disease-free mother plants
·         If no disease-free planting material is available, treat stakes with a solution of 0.3 g active ingredient of metalaxyl/liter, or immerse stakes before planting in hot (49 °C) water for 49 minutes
·                  Use biological control by immersing stakes in a suspension of Trichoderma harzianum and Trichoderma viride at 2.5 x 108 spores/liter, followed by application of the same suspension in drench form. 
Other methods of control of root rots, more suitable for smallholder farmers, include:

·         Application of 200 g/plant of a 1:1 mixture of ash and dry leaves
·         Stake selection
·         Intercropping with cowpea (Vigna unguiculata) 

These practices eliminated root rots in farmer participatory trials conducted in the Colombian Amazon region where root rots are a serious problem.

Witches’ broom disease
Recently (2008) symptoms of a new disease have been observed on cassava in many Asian countries, especially in southern Vietnam, Thailand, Lao PDR, Cambodia, and the Philippines. Plants show excessive sprouting of small leaves having short petioles. If plants are infected early in the growth cycle, they remain small.  Many different varieties are affected, but some more than others. In general, plants are dwarfed and show an exaggerated proliferation of buds, as well as shoots and small branches growing from a single stake. Sprouts have short internodes and many small leaves. The roots of affected plants are thinner and smaller with drastically reduced starch contents.

Witches’ broom disease is mainly spread by the use of infected planting material.

This disease is mainly transmitted by the use of stakes cut from infected plants. It may also be spread by insect vectors, but this is not yet confirmed. To prevent the disease from spreading, the following measures are recommended:

·         Plant varieties that are resistant or that show tolerance to the disease
·         Use only healthy planting material cut from mother plants without any symptoms of the disease
·         Eliminate any diseased plants from the field
·         Rotate cassava with other crops to prevent the transmission of the disease from   infected cassava crop residues left in the field
·         Prevent the movement of planting material from areas where the disease is prevalent to other areas where the disease does not exist 
·         Also, prevent the movement of planting material of related species such as Jatropha, which have a similar disease complex as cassava. 


See more...

Cassava conservation and sustainable development in Vietnam

  Hoang Kim[1], Nguyen Thi Truc Mai[2], Nguyen Bach Mai[3] and Reinhardt Howeler[4]


The project entitled “Vietnam Cassava Conservation and Sustainable Development” has been very successful, as indicated by the results of trials and demonstrations conducted in Tay Ninh, Dak Lak, Phu Yen and Dong Nai provinces, where farmers using the improved technologies and practices boosted cassava yields from 8.5 t/ha to 36 t/ha - a more than four fold increase.

During the period from 1975 to 2015 cassava has become the third most important food crop in Vietnam, after rice and maize. In 2013 the cassava area in Vietnam reached 544,300 ha, with a production of 9.74 million tonnes, and an average yield of 17.9 t/ha. Within Asia, Vietnam is now the third largest cassava producer, after Thailand and Indonesia. Between 1975 and 2000, cassava yields in the country ranged from 6 to 8 t/ha, and the crop was grown mainly for human food and animal feeding.
This changed markedly with the introduction by CIAT in 1988 of some high-yielding breeding lines and varieties from Thailand. Two varieties, Rayong 60 and KU 50, were selected for release in 1993 and 1995 and were named KM60 and KM94, respectively. During the 1990s and the first decade of the 21st Century, Vietnam produced several new cassava varieties, initially mainly selections from sexual seed from Thailand and CIAT, such as KM95-3, SM937-26, KM98-1, KM98-7, but our breeders also made crosses that resulted in the release of the latest new varieties: KM140, KM98-5, KM419 and others. The breeding and adoption of new varieties as well as the development and adoption of more sustainable production practices resulted in a complete transformation of cassava, from a poor man’s food crop to a highly profitable industrial crop. More recently, new advances in cassava cultivation techniques have focused on key demonstration sites in the provinces of Tay Ninh, Dak Lak and Phu Yen using mainly KM419 as a very promising short-duration cassava variety with a fresh root yield of about 35-55 t/ha (28% higher than KM94) and a starch content of about 28-31%. This and other new varieties, together with new advances in cassava cultivation techniques, have yielded spectacular results in trials organized in those three provinces.

The Vietnam National Cassava Program (VNCP) has introduced various methodologies, named “6M” and “10T”, as well as Farmer Participatory Research (FPR), as collaborative experiences that helped to bring advanced technologies into production for millions of poor farmers. This included the s
election of high-yielding varieties and the testing and selection by farmers of locally appropriate technologies. Cassava in Vietnam has great potential but also faces big challenges. At the national level, cassava has become one of the main export crops, which has provided for millions of smallholders an opportunity to increase their yields and improve their standard of living.

Key words:
Cassava, production, utilization, cultivation techniques, achievements, lessons and  challenges, conservation, sustainable development, Vietnam.

Báo Nông nghiệp Việt Nam: Giới thiệu 5 giống sắn mới 
Tuyển chọn 4 giống sắn mới;  Thu hoạch sắn ở Phú Yên

Cassava in Vietnam: Save and Grow, PhuYen

Cassava in Vietnam: Save and Grow DakLak video 1  2, 3
Cassava in Vietnam: Save and Grow, Tay Ninh, video 1

[1] Nong Lam University (NLU), Linh Trung, Thu Duc, Ho Chi Minh City, Vietnam;
2 Hue University of Agriculture and Forestry (HUAF), 102 Phung Hung, Hue, Vietnam;
3 Tay Nguyen University (TNU), 567 Le Duan - Buon Ma Thuot , Dak Lak , Vietnam; 
4 CIAT-Emeritus;

Farmer field day in Dong Xuan, Phu Yen: one of 10T

Bản dịch tiếng Việt
: Quản lý bền vững sắn châu Á, từ nghiên cứu đến thực hành. Tác giả Reinhardt Howeler và Tin Maung Aye. Người dịch: Hoàng Kim, Hoàng Long, Nguyễn Thị Trúc Mai, Nguyễn Bạch Mai, 2015.

(xem tiếp CÂY LƯƠNG THỰC. Bệnh virus khảm lá sắn và cách phòng trừ
Chương 6 Sâu bệnh hại sắn và cách phòng trừ.)



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