White pine weevil management

• Weevil management 
• Sampling to assess weevil attack
• Hazard rating
• Silvicultural methods of control
• Better site selection
• Resistance to attack
• Fertilization and weevil attack

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Silvicultural methods of control

To reduce white pine weevil damage, three options are available:

Open-grown plantation

Close planting reduces damage to Sitka spruce by the white pine weevil in the early years of a plantation. Therefore, thinning should be delayed. High density plantations are also recommended for white pine when the weevil hazard is high and white pine blister rust is low. High density tends to improve tree form after weevilling but pre-commercial thinning will be required after trees have reached a height of 5 m (Stiell 1979). For Sitka spruce, the recommendation is to delay thinning to at least age 25 years. To concentrate growth on the best trees, thinning should be used to remove the most damaged trees. 

Planting under canopy

White pine may achieve a maximum height growth with as little as 45% full sunlight (Stiell 1985). Therefore for the white pine, different practices have been suggested such as the introduction of white pine under an existing overstory, in east-west strip-cuts in conifer or mixed stands (Stiell and Berry 1985). Weevils tend to avoid covered trees because they have small leaders and because the microclimate in dense shade is sub-optimal for the weevil. Growing under a canopy will enhance natural pruning and accelerate recovery following an attack. According to Stiell (1985), 50% full light could be a compromise for weevil control and seedling growth. However, this compromise is not fully accepted and is a matter of debate (Pubanz 1995). 

Mechanical control

Reduction of damage by clipping the infested leaders is a way to manage white pine weevil in small, isolated, young plantations.  This procedure is more effective when an infestation begins. Studies in Quebec demonstrated the efficiency of this technique when done properly at the correct time. Also, subsequent pruning can help correct tree form. Tests are being run to determine if keeping the predators in the plantation helps to further reduce the population and damage (Lavallée et al. 1998). However, attacked leaders should never be cut and left free on the ground because weevils will be able to emerge normally (Lavallée et al. 1993). Clipping in large plantations located in high hazard zones of the interior of British Columbia proved to be ineffective and logistically complicated (Rankin 1994).

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