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.
1. Introduction
Vietnam has made great strides in regreening the country in recent decades
[1][2]. Due to national policies and targets for afforestation and the rehabilitation of natural forests, the forest area expanded from 9.40 million ha in 1990 to 14.67 million ha in 2020
[3]. Vietnam’s 2006–2020 Forest Development Strategy expressed the goal of increasing the total forest cover from 37% in 2006
[4] to 42% by 2020
[3]. Forest development efforts of the past 10 years have greatly contributed to Vietnam’s sustainability strategy
[5]. In particular, the plantation forestry sector has made a significant contribution to the growth in forest cover and now comprises 26.4% (ca. 4.4 million ha) of the total forest area in Vietnam
[3]. About half of the forest plantations are managed by small stakeholders and the remainder by private companies
[3][6]. Therefore, the plantation forest sector is vitally important to the livelihood of millions of rural households
[7][8]. Exotic species, mainly acacias and eucalypts, have been widely planted in Vietnam
[6]. It has been estimated that fast-growing
Acacia hybrids can provide 33–56% of the total household income
[9]. Furthermore, the export of wood and forest products earned US$9.4 billion in 2018
[6] and increased to US$12.3 billion in 2020
[10]. Even though the plantation area has continued to increase over time, it is insufficient to meet the demand of the local wood processing industry
[11]. Reducing losses from damage caused by insect pests and pathogens can help to secure the future wood supply that Vietnam needs for its domestic and international markets.
Over time, the incidence of pest and disease problems in
Acacia and
Eucalyptus stands has increased globally
[12][13][14][15], including in Vietnam. Old et al. described 13 fungal pathogens associated with
Eucalyptus plantations in Vietnam
[16][17]. The most common
Eucalyptus diseases were caused by
Cryptosporiopsis eucalypti,
Cylindrocladium reteaudii, and
Ralstonia solanacearum. Illustrations of the most common biotic problems (21 pests, 23 pathogens) in
Acacia,
Eucalyptus, and
Pinus plantations were provided in a field guide for advisors and growers
[18]. With the exception of native
Pinus, most of the studies on forest health in Vietnam have focused on exotic species, mainly
Acacia and
Eucalyptus [19][20]. Currently, there are five major pest species (
Ericeia sp.,
Helopeltis sp.,
Phalera grotei, Pteroma plagiophleps, and
Xylosandrus crassiusculus) and four major pathogens (
Ceratocystis sp.,
Corticium salmonicolor,
Phytophthora cinnamomi, and
Pythium vexans) threatening the productivity of
Acacia plantations in Vietnam. Furthermore, six major pest species (
Aristobia testudo,
A. approximator,
Biston suppressaria,
Leptocybe invasa,
Sarothrocera lowi, and
Trabala vishnou) and five major pathogens (
Cylindrocladium sp.,
Cryptosporiopsis eucalypti,
Ralstonia solanacearum,
Teratosphaeria destructans, and
T. zuluensis) have been damaging
Eucalyptus plantations. As the research effort on forest health in Vietnam has increased over the past two decades, many reports focusing on individual pests or pathogens of interest have been published
[18][20][21][22][23][24][25][26][27].
2. Field Surveys—General Procedures
Forest health surveys were undertaken annually from 2011 to 2020, in the eight forest geographic regions of Vietnam (Figure 1), with support from the Ministry of Agriculture and Rural Development. Field observations were carried out on forests planted with 16 tree species (Table 1). We relied on information gathered by local foresters as well as our own observations to select the surveyed plantations in each studied forest region. Three fixed plots (40 × 25 m) were randomly set up in plantations comprising the tree species present in each region and they were assessed over ten years. Selected plots were at least 20 m from plantation edges, roads, or forest gaps. About 25% of trees (at least 30 trees) in each plot were randomly selected and assessed for damage from insect pests and/or pathogens. Surveys usually involved three repeat visits a year undertaken in spring (February–April), summer (May–July), and autumn (August–October). Where tree injury was observed (e.g., defoliation, leaf senescence, shoot dieback, tree death), we quantified the damage.
Figure 1. Map of Vietnam showing the eight forest geographic regions.
Table 1. Details of forest plantation species that were surveyed for pests and pathogens.
Host |
Area in 2020 (ha) |
Planting Region * |
Native/Exotic |
Commercial Use |
Acacia spp. and hybrids |
2,000,000 |
NE, NW, NP, NC, SC, HC, SE, SW |
Exotic |
Paper, plywood, timber for construction and furniture |
Ailanthus triphysa |
500 |
NE, NC, SC, SE |
Native |
Plywood |
Chukrasia tabularis |
35,000 |
NE, NW, NP, NC, SC, HC |
Native |
Timber for furniture |
Cinnamomum cassia |
210,000 |
NE, NW, NC, SC |
Native |
Bark for export and seasoning, oil for medicine |
Dalbergia tonkinensis |
2000 |
NE, NW, NP, NC, SC, HC, SE |
Native |
Timber for furniture and handcrafts |
Dendrocalamus barbatus |
120,000 |
NE, NW, NP, NC |
Native |
Culm for construction, activated carbon, handcrafts and paper, young shoots for food |
Dendrocalamus latiflorus |
15,000 |
NE, NW, NP, NC, SE |
Exotic |
Young shoots for food, culm for paper |
Dipterocarpus alatus |
20,000 |
NC, SC, HC, SE |
Native |
Timber for furniture, construction |
Eucalyptus spp. and hybrids |
400,000 |
NE, NW, NP, NC, SC, HC, SE, SW |
Exotic |
Paper, plywood, timber for construction |
Fernandoa brilletii |
6000 |
NE, NW, NC |
Native |
Timber for furniture |
Hopea odorata |
20,000 |
NC, SC, HC, SE |
Native |
Timber for furniture and boat |
Illicium verum |
42,000 |
NE, NW |
Native |
Fruit for export and seasoning, oil for medicine |
Melaleuca cajuputi |
36,000 |
NE, NP, NC, SC, SW |
Native |
Paper, activated carbon, poles for construction |
Melaleuca leucadendra |
32,000 |
SE, SW |
Exotic |
Paper, activated carbon, poles for construction |
Nauclea orientalis |
500 |
SE, SW |
Native |
Plywood |
Neolamarckia cadamba |
1000 |
NE, NC, SE, SW |
Native |
Plywood |
* Forest zones (see Figure 1): NE, North East; NW, North West; NP, North Plain; NC, North Central; SC, South Central; HC, Highland Central; SE, South East; SW, South West.
3. Field Surveys—Insects
Insect survey methods included eye tracking, sweep netting, suction sampling, and lure traps. Adult folivores were captured with collecting nets on aluminum poles, and placed in killing jars. Plastic boxes (VietNhat Plastic Joint Stock Company, Hanoi, Vietnam) with nylon mesh covers were employed to transport the living larvae, pupae, and eggs to the laboratory. Fresh leaves were included for the larvae to feed.
For wood borers, samples were mostly obtained by the felling of affected trees, then chopping logs to obtain collections. When adults were not present, logs 1.0–1.5 m in length were transported to the laboratory in Hanoi. Some logs were dissected to capture the adults and/or larvae. The cuts of other logs were sealed with Parafilm® (Bemis Company Inc., Neenah, WI, USA) and were taken to the laboratory for rearing adults for identification.
In addition, more intensive sampling was undertaken through trapping in the field for adult ambrosia beetles. Black funnel Lindgren traps (BioQuip Products, Inc., Compton, CA, USA) and self-made plastic-bottle traps baited with 70% ethanol and para-menthenol (1S, 4R)-p-menth-2-en-1-ol) (Synergy Semiochemicals Corp. (Burnaby, BC, Canada) were used to attract adults. Propylene glycol (Merck, Darmstadt, Germany) and water (50:50) solution was used in the collection cups. Each trap was suspended at least 10 m apart in a plantation and 1.5 m above the ground to avoid damage by wild animals. The baits were replaced once a week. Baiting was undertaken from April to June. Trap collections were stored in 70% ethanol in Eppendorf® (Eppendorf Manufacturing Corp., Hamburg, Germany) tubes and then sorted in the laboratory.
4. Change over Time
Forest health surveys undertaken from 2011 to 2020 on the plantations of different tree species in Table 1 revealed 14 new or emerging insect pest species and major disease threats from two plant pathogens (Table 2). The total number of new or emerging insect pest species and pathogens increased from 2 in 2011 to 17 in 2020 (Figure 2). Hence, on average, 1–2 new pests per year were recorded damaging forest plantations in Vietnam. The temporal and geographical occurrence of the observed pests and pathogens is detailed in Table 3. Of particular note is the apparently rapid spread of Aulacapsis tubercularis in Cinnamomum cassia, Euwallacea fornicatus in Acacia spp. and C. cassia, Tapinolachrus lacordairea in Chukrasia tabularis, and Xyleborus perforans in Acacia and Eucalyptus. The two main types of damage from insect pest species are from foliar feeding by folivores (5 species of Lepidoptera), and bark and/or wood feeding (6 species of Coleoptera). The fungal pathogen Ceratocystis manginecans has extended its host range from exotic Acacia and Eucalyptus to the native Dalbergia tonkinensis and C. tabularis.
Figure 2. Change in the number of pest and pathogen species recorded each year.
Table 2. Pests and pathogens recorded in forest health surveys in Vietnam causing significant damage to host trees.
Group |
Species |
Tree Species |
Damaged Part |
Pests |
Coleoptera |
Batocera lineolata |
Eucalyptus hybrids |
Boles |
Euwallacea fornicatus |
Acacia auriculiformis Acacia mangium Acacia hybrids Cinnamomum cassia |
Boles |
Lycaria westermanni |
Fernandoa brilletii |
Leaves |
Tapinolachnus lacordairei |
Chukrasia tabularis |
Boles |
Xyleborus perforans |
Acacia hybrids Eucalyptus urophylla |
Boles |
Xystrocera festiva |
Acacia mangium |
Boles |
Hemiptera |
Aulacaspis tubercularis |
Cinnamomum cassia |
Leaves |
Helopeltis theivora |
Acacia auriculiformis Acacia mangium Acacia hybrids Cinnamomum cassia Melaleuca cajuputi Melaleuca leucadendra |
Young leaves, shoots |
Lepidoptera |
Antheraea frithi |
Dipterocarpus alatus Hopea odorata |
Leaves |
|
Arthroschista hilaralis |
Neolamarckia cadamba Nauclea orientalis |
Leaves |
|
Atteva fabriciella |
Ailanthus triphysa |
Young leaves, shoots |
|
Krananda semihyalina |
Cinnamomum cassia |
Leaves |
|
Moduza procris |
Neolamarckia cadamba Nauclea orientalis |
Leaves |
Orthoptera |
Hieroglyphus tonkinensis |
Dendrocalamus barbatus Dendrocalamus latiflorus |
Young leaves |
Pathogens |
Fungi |
Ceratocystis manginecans |
Acacia auriculiformis Acacia mangium Acacia hybrids Chukrasia tabularis Dalbergia tonkinensis Eucalyptus camaldulensis Eucalyptus urophylla |
Boles |
Fusarium solani |
Dendrocalamus latiflorus |
Shoots, roots |
Oomycete |
Phytophthora acaciivora |
Acacia mangium Acacia hybrids |
Roots and dieback of seedlings |
Table 3. Temporal and geographical occurrence of pest and pathogen species in forest health surveys in Vietnam from 2011 to 2020.
Organism |
2011 |
2012 |
2013 |
2014 |
2015 |
2016 |
2017 |
2018 |
2019 |
2020 |
Pest |
Antheraea frithi |
|
|
|
|
|
|
SE |
SE, SW |
SE, SW |
SE, SW |
Arthroschista hilaralis |
|
|
|
|
SW |
SW |
SW |
SW |
SW |
SW |
Atteva fabriciella |
|
|
|
|
|
NE |
NE |
NE |
NE |
NE |
Aulacaspis tubercularis |
|
|
|
|
SW |
SW, SC |
SW, SC, NE, NP |
SW, SC, NE, NP |
SW, SC, NE, NP |
SW, SC, NE, NP |
Batocera lineolata |
|
|
|
|
|
|
|
|
NW |
NE, NW |
Euwallacea fornicatus |
|
|
NE, SC, HC |
NE, SC, HC |
NE, SC, HC |
NE, NW, NC, SC, SE, HC |
NE, NW, NC, SC, SE, HC |
NE, NW, NC, SC, SE, HC |
NE, NW, NC, SC, SE, SW, HC |
NE, NW, NC, SC, SE, SW, HC |
Helopeltis theivora |
|
|
|
|
|
|
|
|
|
NC, NW, NE, HC, SE, SW |
Hieroglyphus tonkinensis |
NW, NE, NC |
NW, NE, NC |
NW, NE, NC |
NW, NE, NC |
NW, NE, NC |
NW, NE, NC |
NW, NE, NC |
NW, NE, NC |
NW, NE, NC |
NW, NE, NC |
Krananda semihyalina |
|
|
|
|
|
|
|
|
|
NE, NP |
Lycaria westermanni |
|
|
|
|
|
|
|
NC |
NC, NE, NW |
NC, NE, NW |
Moduza procris |
|
|
|
|
SW |
SW |
SW |
SW |
SW |
SW |
Tapinolachnus lacordairei |
|
|
|
|
|
|
|
|
NW |
NE, NW, NC |
Xyleborus perforans |
|
|
|
|
|
|
|
|
NE |
NE, SE, SW |
Xystrocera festiva |
|
|
HC |
HC |
HC |
HC, SC |
HC, SC |
HC, SC |
HC, SC |
HC, SC |
Pathogen |
Ceratocystis manginecans |
NE, NW, NC |
NE, NW, NC |
NE, NW, NC |
NE, NW, NC, SE |
NE, NW, NP, NC, SE, SW |
NE, NW, NP, NC, SC, SE, SW |
NE, NW, NP, NC, SC, HC, SE, SW |
NE, NW, NP, NC, SC, HC, SE, SW |
NE, NW, NP, NC, SC, HC, SE, SW |
NE, NW, NP, NC, SC, HC, SE, SW |
Fusarium solani |
|
|
|
|
|
|
|
|
NE |
NE |
Phytophthora acaciivora |
|
|
NE |
NE |
NE |
NE |
NE |
NE |
NE |
NE |
Note: NE. North East; NW. North West; NP. North Plain; NC. North Central; SC. South Central; HC. Highland Central; SE. South East; SW. South West.