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.
Melaleuca leucadendra and M. cajuputi are grown widely in Vietnam, with plantation areas in 2020 of 32,000 ha and 36,000 ha respectively. A stem borer, Neurozerra conferta (Walker) (Lepidoptera: Cossidae), has significantly damaged plantations of both species. Field surveys in 2021 found N. conferta damage to M. leucadendra in the four provinces of Ninh Binh, Long An, Dong Thap and Kien Giang with a damage incidence (P%, percentage of plants attacked) of 22.4–33.2% and an average damage index (DI) of 0.77–1.01. In Long An province, surveys in 2022 found frequent damage to M. leucadendra plantations at the age of 2–3 years with P% ranging from 22.7 to 27.3% and DI from 0.46 to 0.54. Beauveria bassiana and Metarhizium anisopliae were identified as potential biological agents with control effectiveness of 59.6–63.3%. Screening to identify resistant varieties of M. leucadendra and development of an integrated pest management strategy for N. conferta are recommended.
Acacia mangium plantations account for more than 50 % of the exotic plantations in Vietnam. A new black butt symptom was discovered in 2012, followed by the wilting sign in Acacia seedlings in Tuyen Quang Province. Isolations recovered two Phytophthora species, the well-known Acacia pathogen P. cinnamomi, and an unknown species. The new species is described here as Phytophthora acaciivora sp. nov. Phylogenetically this species resides in clade 2d and is most closely related to P. frigida. Phytophthora acaciivora is a heterothallic species, oospores are aplerotic and antheridia are amphigynous. It produces predominantly elongated ovoid, semi papillate, persistent sporangia, no hyphal swellings and no chlamydospores. Optimum temperature for the growth is 25–30 °C and the maximum temperature is over 37.5 °C. Studies are underway to determine the impact of this new species on Acacia plantations 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: <25%, 25%–50% and >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.
Table S1: Sequences of Euwallacea spp. used for phylogenetic analysis in this study Scientific name Common name Location Accession number Reference Euwallacea fornicatus PSHB Phu Yen -Vietnam KU727011 (Smith et al. 2019) Euwallacea fornicatus PSHB Yen Bai -Vietnam KU727021 (Smith et al. 2019) Euwallacea fornicatus PSHB Dong Nai -Vietnam KU727022 (Smith et al. 2019) Euwallacea fornicatus PSHB Okinawa -Japan KU727027 (Smith et al. 2019) Euwallacea fornicatus PSHB Ilan County -Taiwan KU727028 (Smith et al. 2019) Euwallacea fornicatus PSHB Ninh Binh -Vietnam MN266861 (Cognato et al. 2020) Euwallacea fornicatus PSHB Yen Bai -Vietnam
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