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Competence Network Climate Change, Risk Management and Transformation in Forest Ecosystems

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Forest Research Institut Baden-Württemberg (FVA)
Department of forest economics

Wonnhaldestr. 4
D-79100 Freiburg

Tel:  +49 761 4018 231
Fax: +49 761 4018 333

Article

Author(s): Hansjochen Schröter, Holger Veit, Jutta Odenthal-Kahabka
Editorial office: FVA, Germany
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Prevention and Control of Wood Boring Insects

Conifer ambrosia beetle (Trypodendron lineatus) and large timberworm (Hylecoetus dermestoides) are particularly important wood boring species. They can do considerable economical damage mostly to stored timber.

Werftkäfer-Larve
Pic. 1: Larvae of the conifer ambrosia beetle. (Photo: H. Veit)

The rise in beetle populations over the last years is based on the following factors:

  • Due to rising economic pressures and high costs, timber harvesting operations have been rationalised. Modern, close-to-nature forestry practises result in higher amounts of residual and dead wood, an ideal breeding ground and habitat for wood boring insects.
  • Timber felled during fall/ winter, (whether by storm or logging) which is not removed but left unprotected in the forest, will be extremely susceptible to infestation due to low wood moisture the next spring. Storm damaged timber which was felled by late winter/ spring storms (e.g. "Wiebke" and "Vivian" 1990) proved to be a lot less susceptible, especially to infestation by early flying species, as it was still too moist.
  • Insufficiently irrigated timber in wet storage is also at high risk in spring.
  • Insects have developed well during the comparatively warm and dry recent summers. Many species were able to complete more and shorter generation cycles. Trees were under stress and therefore more susceptible to infestation.

General preventive measures

  • Removal of (coniferous) timber to a place outside the forest (or into hardwood stands) as quickly as possible during times of insect flying and where infestations have already started.
  • Use storage sites free from local insect populations; storage outside of the forest, avoid sites with infestations in the previous year.
  • Storage of roundwood: dry storage of debarked timber, wet storage on irrigation sites or conservation under oxygen exclusion.

Protection of individual objects

Apply insecticides which are permitted for use against wood boring insects and labelled "straight after beginning infestation" to protect high-value timber in storage. Limit application to a few exceptional cases based on experiences from the previous year, e.g. for the protection of valuable timbers like oak stems. At the time of writing, the only insecticide approved for use against the large timberworm in Germany is KARATE ZEON by Syngenta. It may be applied to soft- and hardwood as a precautionary measure before the beetles fly. After large-scale calamities like "Lothar", forest enterprises usually reach the upper limit of their organisational, as well as labour, machinery and storage, capacities. Infestations by wood boring insects may not always be prevented. Forest enterprises will have to decide whether to accept considerable economic losses due to the degradation of high quality timber or to take measures to protect and preserve timber quality.

Future prospects

Timberworms can occur on stump and stocks of all managed sites (especially wet and shady sites). They are therefore potentially present almost area-wide. Storms and other large-scale calamities can expand breeding ground capacities dramatically. Therefore the large timberworm will primarily have its highest impact after calamities which bring with them problems with logging and conversion of damaged timber and flooding the timber market. Serious infestation is not to be expected during "regular" logging operations which involve speedy removal of logs.

Guideline for integrated forest protection against wood boring insects

Aim Basic principle Measures
Clean forestry practice
  • Lower reproduction rate by depriving breeding grounds
  • Prevention
  • Strategic planning of labour, machinery, timber market and storage capacities
  • High degree of conversion
  • (e.g. using harvesters)
  • Speedy removal of timber to somewhere outside the forest
  • Burning, chaffing or mulching of residual timber
  • No accumulation of fresh dead wood
Storage of roundwood
  • Preserving quality of high-value timber
  • High-value timber only (no compromises!), green timber only: moisture 30 - 120%
  • Not exclusively for prevention of wood-breeding insects
  • No general wood-breeding insect control measures
  • Avoid humid sites (wood-boring beetles, fungi), especially sites with infestations during the previous year, even for short-term storage
  • Never put already infested timber in storage
  • Storage over bark is not recommended where high beetle populations are expected, risk of infestation is too high
  • Dry storage of debarked heavy softwood logs cut in winter: put in storage before March/April, airy and warm locations, shaded or roofing, with the long side facing windward side, continuous monitoring, maximum length of storage one vegetative period. See also Dry Storage
  • Wet storage: speedy (within 14 days after cutting) rolling in of untreated (!) timber; timber with infestation of wood boring insects only when processed at an early stage (crown still intact)
Infestation monitoring
  • Basis of planning effective counter measures (Start and progression of infestation)
  • Proper identification of the insect species is very important due to the differing living and breeding conditions and hence differing remedial measures required. Seek specialist advice if unsure.
  • Continuous monitoring throughout the whole vegetative period, beginning mid-February (depending on weather development, 12 °C); all wood-boring insects (including the early flyers) can infest timber well into autumn
  • White bore dust, consistency is a pointer to the species, accumulation on log surfaces
  • Bore holes (diameter and density) in bark (not all species) and wood
  • Larval galleries in wood, to some extent in bark
Pheromone traps
  • Monitoring swarm progression of conifer ambrosia beetles (careful timing of infestation checks)
  • Facultative
  • Monitoring purposes only
  • Personnel and material planning
  • One monitoring series per forestry department (map elevation), trap sites should be easily accessible
  • Begin mid-February (in warmer localities)
  • Not in the immediate vicinity of timber storage sites
  • Check every 1-2 weeks, depending on swarm progression and weather conditions
  • Single traps for monitoring purposes
  • Empty and check lure regularly, renew lure twice per vegetative period, record bycatch
  • Documentation (swarm progression)
Insecticides
  • Quality assurance for high-value timber (protection of individual objects)
  • Protection of adjacent stands
  • Legal basis: expertise, distance to water bodies, regulations on protected areas, certification requirements (FSC, PEFC,…), occupational health and safety
  • Approved agents only (consider: verification of effectiveness is not legally required of supplier)
  • Check regulatory approval of agents for respective species
  • Consider customers’ requests
  • Not a preventive measure

  • Application only after all other means are exhausted
  • Only where danger is imminent (after primary infestation is found), check with customer
  • Application to roundwood both over and under bark possible
  • No application inside the stands, only apply to roundwood concentrated on roadsides
  • Insecticides are designed for single stem application, stack application will result in lower effectiveness depending on stack height (approx. 60 % effectiveness for 3.5 metres height). This is usually adequate for the beetles
  • Time application according to life cycle of the target species
  • Protection of adjacent stands by preventive spraying only where target species are wood borers that can switch to infestation of standing trees, e.g. larch borer, small white-marmorated longhorned beetle, oak-infesting wood borers. Seek expert advice if unsure.
  • Marking of treated stacks (agent, species, date), documentation in timber lists

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