Growing eastern white pine under a hardwood overstory with 40-50 percent crown closure can reduce weevil attacks while still providing sufficient light for healthy growth. Shade reduces high temperatures that are preferred by females. Growing trees in the shade also reduces the growth of the leader, causing it to be less vigorous with thinner bark, which is not as attractive to white pine weevil.
Growing eastern white pine in high densities can also significantly reduce the chance of weevil attack. Creating competition with high planting densities forces rapid height growth with minimal terminal diameter growth, causing trees to reach heights of 20 feet faster and be less attractive to weevils. Competition also forces lateral shoots to straighten if the terminal leader is killed by white pine weevil.
In small plantations or Christmas tree farms, monitoring for and destroying infested terminals might be worthwhile. Monitor for wilting terminals on warm, sunny days in the spring. Wilting terminal leaders can be pruned and destroyed before late July. Alternatively, removing all but one live lateral shoot directly below any affected terminal will promote single-stem dominance.
If any white pine weevil damage is unacceptable to you, insecticides can reduce local populations. If resin droplets from adult feeding on the previous year's growth are detected on two to five percent of trees in late March and April, apply to the terminal leader only, using an insecticide labeled for use on trees.
A combination of chemical control with pruning provides the best results. Several natural enemies and predators (e.g., birds, voles, parasitic flies) exist but do not provide enough control to prevent attacks.
White pine weevils are only threatening when white pines are young. A little white pine weevil damage is not detrimental to a young white pine's health, and the damage can simply be pruned away. If several lateral branches are competing to be the terminal leader, all but one can be pruned away. This will help the tree correct its form.
There are two ways to lessen weevil populations on young white pines in yards:
- Monitor for wilting terminal shoots in early summer, and prune out and destroy infested terminal shoots before late July, when adult weevils emerge to overwinter; or
- Apply an insecticide to the ends of upper branches to target egg-laying adult weevils in the spring, generally in April.
Other Sources of Information
How to manage eastern white pine to minimize damage from blister rust and white pine weevil -USDA Forest Service »