New and emerging insect pest and disease threats to forest plantations in Vietnam

The planted forest area in Vietnam increased from 3.0 to 4.4 million hectares in the period 2010–2020, but the loss of productivity from pests and diseases continues to be a problem. During this period, frequent and systematic plantation forest health surveys were conducted on 12 native and 4 exotic genera of trees as well as bamboo across eight forest geographic regions of Vietnam. Damage caused by insects and pathogens was quantified in the field and laboratory in Hanoi. The threats of greatest concern were from folivores (Antheraea frithi, Arthroschista hilaralis, Atteva fabriciella, Hieroglyphus tonkinensis, Lycaria westermanni,Krananda semihyalina, and Moduza procris), wood borers (Batocera lineolata, Euwallacea fornicatus, Tapinolachnus lacordairei, Xyleborus perforans, and Xystrocera festiva), sap-sucking insects (Aulacaspis tubercularis and Helopeltis theivora) and pathogens (Ceratocystis manginecans, Fusarium solani, and Phytophthora acaciivora). The number of new and emerging pests and pathogens increased over time from 2 in 2011 to 17 in 2020, as the damage became more widespread. To manage these pests and diseases, it is necessary to further invest in the selection and breeding of resistant genotypes, improve nursery hygiene and silvicultural operations, and adopt integrated pest management schemes. Consideration should be given to developing forest health monitoring protocols for forest reserves and other special-purpose forests

Nothophytophthora gen. nov., a new sister genus of Phytophthora from natural and semi-natural ecosystem

During various surveys of Phytophthora diversity in Europe, Chile and Vietnam slow growing oomycete isolates were obtained from rhizosphere soil samples and small streams in natural and planted forest stands. Phylogenetic analyses of sequences from the nuclear ITS, LSU, β-tubulin and HSP90 loci and the mitochondrial cox1 and NADH1 genes revealed they belong to six new species of a new genus, officially described here as Nothophytophthora gen. nov., which clustered as sister group to Phytophthora. Nothophytophthora species share numerous morphological characters with Phytophthora: persistent (all Nothophytophthora spp.) and caducous (N. caduca, N. chlamydospora, N. valdiviana, N. vietnamensis) sporangia with variable shapes, internal differentiation of zoospores and internal, nested and extended (N. caduca, N. chlamydospora) and external (all Nothophytophthora spp.) sporangial proliferation; smooth-walled oogonia with amphigynous (N. amphigynosa) and paragynous (N. amphigynosa, N. intricata, N. vietnamensis) attachment of the antheridia; chlamydospores (N. chlamydospora) and hyphal swellings. Main differing features of the new genus are the presence of a conspicuous, opaque plug inside the sporangiophore close to the base of most mature sporangia in all known Nothophytophthora species and intraspecific co-occurrence of caducity and non-papillate sporangia with internal nested and extended proliferation in several Nothophytophthora species. Comparisons of morphological structures of both genera allow hypotheses about the morphology and ecology of their common ancestor which are discussed. Production of caducous sporangia by N. caduca, N. chlamydospora and N. valdiviana from Valdivian rainforests and N. vietnamensis from a mountain forest in Vietnam suggests a partially aerial lifestyle as adaptation to these humid habitats. Presence of tree dieback in all forests from which Nothophytophthora spp. were recovered and partial sporangial caducity of several Nothophytophthora species indicate a pathogenic rather than a saprophytic lifestyle. Isolation tests from symptomatic plant tissues in these forests and pathogenicity tests are urgently required to clarify the lifestyle of the six Nothophytophthora species.info:eu-repo/semantics/publishedVersio

Emerging disease problems in eucalypt plantations in Lao PDR

Surveys of nurseries and plantations of Eucalyptus species were conducted within Lao PDR in 2009. A range of pathogens were isolated including species within Phytophthora, Pythium, Fusarium, Colletotrichum, Neofusicoccum, Lasiodiplodia, Pilidiella, Calonectria, Cryptosporiopsis, Corticium and Teratosphaeria. Some diseases caused significant defoliation and loss of stock within nurseries and plantations. The presence of these diseases in combination with a changing climate poses many challenges for the future sustainable and profitable management of plantations in Lao PDR

Sustainable management of plantation eucalypts and acacias in Asia

The long-term productivity of short-rotation plantation eucalypts and acacias in Asia requires ongoing investment in the biology of current and new genetics and constraints that climate change may impose. Understanding site fertility constraints has the potential to further lift productivity through precision application of inorganic fertilizers, management of beneficial bacteria and fungi and appropriate slash management. It remains a concern that nutrient disorders, especially micronutrients, which could be easily corrected in acid soils, are still being widely reported in the region. The low genetic diversity in many plantations heightens the risk of productivity loss due to incursions of pathogens and pests. In the past decade, a number of new biotic eucalypt threats have appeared within the region and are rapidly spreading. No plantation estate can be considered to be risk-free from such incursions. Furthermore, abiotic stresses (e.g. water, nutrients) are likely to exacerbate damage from biotic agents. With climate change, plantations established on marginal lands and sites with poor soils are likely to experience stresses that are more frequent and a more diverse group of stress agents than those in areas that are more resilient to climate change. Future breeding programs should include selection for tolerance to key abiotic and biotic stress agents that have the highest risk to plantation productivity

Ceratocystis sp. causes crown wilt of Acacia spp. planted in some ecological zones of Vietnam

The plantation area in Vietnam of Acacia auriculiformis, A. mangium and their hybrid has expanded greatly in the last decade. Recently, a new stem canker disease causing symptoms of crown wilt, followed by wood discoloration then death of infected trees has occurred in many ecological zones. Ascomata were obtained by incubating discolored wood pieces in moist chambers or by carrot baiting. Isolates of fungi were obtained on PDA medium by taking spores emerging from the tips of ascomata necks. Ceratocystis was identified based on ascospore morphology and conidial types. Twenty six isolates of Ceratocystis were used for pathogenicity assessment on 8-month old seedlings of A. mangium in a nursery, with 5 seedlings per isolate. Stems were inoculated by inserting an 8 mm diameter PDA plug covered with 15-day old mycelia onto the cambium about 50 cm above the ground. Five seedlings were inoculated with sterile PDA plugs to serve as the control. The wounds and plugs were sealed with parafilm to protect them against desiccation and rain. After 60 days of inoculation, based on lesion development and tree death, the pathogenicity of the isolates were identified: 2 isolates (AA8, AMH12) nil, 4 isolates (AAHX1, AMH40, AMD26, AHDL1) low, 4 isolates (AA22, AMH9, AMMB7, AHXL3) moderate, 3 isolates (AMBL3, AMPL2, AMH5) high, and 13 isolates (AA54, AA62, AMH24, AMH26, AMH41, AMHX1, AMQN1, AMBL4, AHBB1, AHBD1, AHBP1, AHXL1 and AHXL2) very high level of pathogenicity causing plant death. This is the first record of Ceratocystis causing damage to Acacia plantations in Vietnam. The origin of the pathogen is unknown. Work is progressing to determine whether the species is the same as that known to cause damage to A. mangium plantations in Indonesia

Management of needle-eating caterpillars associated with Pinus massoniana and P. merkusii in Vietnam

Pine tussock moth (Dasychira axutha Collenette (Lymantriidae)) and masson pine caterpillar (Dendrolimus punctatus Walker (Lasiocampidae)) cause serious damage to Pinus massoniana and P. merkusii plantations in Vietnam. An integrated pest management (IPM) program is required to control these pests. Therefore, this study was undertaken to identify damage thresholds and to evaluate control options for implementing IPM in the Northeast and North Central regions of Vietnam. Three damage thresholds were considered: 50% loss of leaf area. Control options were manual collection of eggs and pupae and the use of light traps and biological agents. An initial IPM model was developed for each pest and these gave control efficacies of 82.4% (Da. axutha on P. massoniana) and 77.8% (De. punctatus on P. merkusii). Six extended IPM models were undertaken by forest companies giving pest control efficacies of 79.2%–85.9%. The collection of pine resin provides an important source of income to local communities and the resin yield in the IPM models increased by 20.9%–22.7% compared to untreated control plots. The IPM protocols would help in developing policies that promote a more sustainable management of forest pests in Vietnam, thus reducing dependence on the use of insecticides of environmental and public health concerns

Invasive plant species in the national parks of Vietnam

The impact of invasive plant species in national parks and forests in Vietnam is undocumented and management plans have yet to be developed. Ten national parks, ranging from uncut to degraded forests located throughout Vietnam, were surveyed for invasive plant species. Transects were set up along roads, trails where local people access park areas, and also tracks through natural forest. Of 134 exotic weeds, 25 were classified as invasive species and the number of invasive species ranged from 8 to 15 per park. An assessment of the risk of invasive species was made for three national parks based on an invasive species assessment protocol. Examples of highly invasive species were Chromolaena odorata and Mimosa diplotricha in Cat Ba National Park (island evergreen secondary forest over limestone); Mimosa pigra, Panicum repens and Eichhornia crassipes in Tram Chim National Park (lowland wetland forest dominated by melaleuca); and C. odorata, Mikania micrantha and M. diplotricha in Son Tra Nature Conservation area (peninsula evergreen secondary forest). Strategies to monitor and manage invasive weeds in forests and national parks in Vietnam are outlined

Market and policy setting for the trade in Dalbergia tonkinensis, a rare and valuable rosewood, in Vietnam

Dalbergia tonkinensis (Fabaceae) is one of the most valuable rosewood furniture species in the world and, although threatened in the wild, is being traded in local markets in north Vietnam. Trade in D. tonkinensis was investigated by compiling information from interviews, published and unpublished articles, and reports of forest rangers and market regulators. Goods traded included seed, seedlings, living trees, heartwood, handcrafts and furniture. Trees for transplanting ranged in value from 43.5-87.0 USD for a small tree to 434.8-4,347.8 USD for larger trees. The price of heartwood varied greatly depending on size, from 13.0 USD/kg (diameter = 6 cm) to 152.2 USD/kg (diameter = 20 cm). High quality furniture sold for 0.4-1.1 million USD. In the period 2011 to 2018, 905.2 tons of heartwood was traded valued at 16.5 million USD. Two thirds of D. tonkinensis wood being traded came from home gardens in 18 provinces. Vinh Phuc province was the largest provider of trees and also had networks of wood purchasing and processing villages. There is now a more open policy towards an emerging D. tonkinensis industry in Vietnam and regulations encourage communities and households to plant D. tonkinensis

Vegetative propagation of Dalbergia tonkinensis, a threatened, high-value tree species in South-east Asia

Dalbergia tonkinensis (Fabaceae) is one of the most valuable rosewood furniture species in the world. Although all species of Dalbergia are now included in Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora, the threat from illegal harvesting remains. Plantation establishment of D. tonkinensis is in its infancy and requires the development of clonal propagation and nursery technology. Cutting experiments were therefore conducted to identify the efficacy of rooting hormones (IAA, IBA and NAA at 0.5, 1.0, 1.5 and 2.0 g L−1), rooting substrate (gravel, river sand and soil), season (spring, summer, autumn and winter), cutting length (10, 20 and 30 cm) and age of the mother tree (1, 5, 10, 15 and 20 years). Cuttings treated with IBA at a concentration of 1.5 g L−1 had the highest rooting percentage and number of roots, attaining 92.2% and 12.3 roots cutting−1 after 45 d, respectively. Rooting percentage and number of roots increased when cuttings were taken in spring and autumn, with the highest mean root length in spring. The rooting ability of cuttings was highest when collected from mother trees at 1 and 5 years old, after which the rooting ability decreased with age. The substrate did not affect the rooting percentage of cuttings but mean root numbers and mean root lengths of cuttings in river sand were higher than those in the other two substrates. Cutting length did not affect the rooting ability of D. tonkinensis cuttings. These results will be used to establish clonal propagation of superior mother trees for commercial and conservation planting of this threatened species in Vietnam

Management of Ceratocystis manginecans in plantations of Acacia through optimal pruning and site selection

Wilt disease has become a threat to Acacia plantations in SE Asia. There are about 1.3 million ha of Acacia auriculiformis, A. mangium and Acacia hybrid plantations in Vietnam that require management of wilt disease caused by Ceratocystis manginecans. To identify options for management, we examined affect of pruning (tree age, pruning time and pruning technique) and site traits (altitude, slope and position) on disease expression from natural infections. Ceratocystis wilt disease and disease indices were more serious in younger than older pruned trees. Pruning in the rainy season resulted in heavier infection by Ceratocystis than pruning in the dry season. Decreasing bark tearing during pruning reduced the levels of infection and disease. Tip pruning of branches reduced disease compared to pruning close to the trunk. The interaction effects of terrain factors showed that A. auriculiformis and Acacia hybrid plantations were most severely affected when trees were planted in foot-hills, at altitudes below 300 m and on slopes below 15o. Results for the pruning time and pruning technique trials have application for reducing the impact of Ceratocystis wilt disease in Acacia plantations in Vietnam