Spruce Beetle Management

Detection

Spruce beetle infestations are usually located first by aerial surveys (aerial overview or detailed heli-GPS) or other sources, and are surveyed on the ground using a two-stage system:

  • The first survey, the walkthrough, is a “coarse filter” that quickly determines the extent of the infestation and any options available based on sanitation harvest index thresholds calculated according to a formula. In most cases, sufficient information for selecting a management option can be obtained from walkthrough data. A treatment decision is then based on the intensity of infestation, beetle life cycle, and other management considerations
  • If more detailed information is required to describe the location and size of an infestation, detailed probes gather more precise information to clarify management alternatives.

Strategies

Choice of management strategies will depend on:

  • size and pattern of the infestation
  •  severity of the attack in each of the last three years
  • vigour and survival of the new broods
  • stand hazard
  • integrated resource management issues/constraints
  • existing and future access
  • harvesting operability

Treatment

Some spruce beetle treatments differ from those of other bark beetles. Treatment timings may differ due to variations in life cycle. Timings of management activities for spruce beetle are given in the following table:

After detection, treatment options are limited to a few general tactics:

  • sanitation harvesting — maximizes extraction of currently infested spruce stands to reduce the existing population and prevent spread.
  • salvage harvesting — primarily conducted to recover damaged timber before it loses its value. This tactic does not reduce spruce beetle populations, but is the first step in returning the site to forest production.
  • trap trees (conventional only) — are living, large-diameter spruce that are felled to attract spruce beetle, which prefer downed material. Trap trees may absorb up to 10 times the number of beetles of a standing tree, and from up to 0.4 kilometres away. 
  • prevention (including hauling restrictions) — restrictions on hauling and milling of infested logs may be necessary if the hauling destinations are adjacent to high-hazard spruce stands. If hauling is permitted at the beginning and end of the spruce beetle flight, logs must be milled within 24 hours. In sanitation-logged areas, long butts, tops greater than 10 centimetres in diameter, decked logs, and stumps containing mature spruce beetle adults may exist. Maturing beetles will emerge to attack new hosts unless the infested material is either burned or removed and milled, or otherwise treated. Stumps should be cut as low as possible.

Hazard and risk rating

Hazard rating identifies stands where substantial losses can be expected if an outbreak occurs, and which are highly susceptible to attack. Once all spruce stands in an area are rated, resources can be directed toward those with the highest hazard, so losses can be minimized. Hazard rating considers stand age, host basal area, stand density, and elevation. Ratings can be used to set priorities for surveys and treatments, and may be used during preparation of forest development plans as a tool in preventive management. High hazard stands have: 

  • an average spruce dbh greater than or equal to 41 cm
  • a spruce volume exceeding 300 m³ /ha
  • more than 65 per cent spruce in well-drained creek bottoms

Stand risk is the probability a stand will be attacked or re-attacked based on proximity and incidence of a spruce beetle infestation. If not currently infested, the stand may be attacked by spruce beetle adults immigrating from adjacent infested stands. Any susceptible stand within two km of a spruce beetle infestation would be at high risk. Stands with high hazard and risk values have a high priority for management.

Further Reading