The white pine weevil is a native North American insect that poses a serious threat to spruce and pine trees across the continent, mostly in the northern US and Canada. Not to be confused with western pine beetle, the white pine weevil infests and kills the terminal leader of young trees. This leads to bushy-topped trees, stunted growth, and trees with multiple leaders. In our area, the white pine weevil is most common in Colorado or blue spruce.
The adult weevil is an inconspicuous brown ¼ inch weevil. At this stage, they can be seen crawling on trees, but its other life stages occur beneath the bark of trees, making it impossible to spot until the damage becomes evident. The larvae are white grubs with reddish-brown heads. These can only be seen by scraping away the outer bark of infested trees. Adult weevils overwinter in soil litter under host trees. Once spring temperatures rise to 50 degrees F consistently, they become active. Egg-laying females crawl up the host trees and lay eggs in tiny holes that they have chewed into the tree’s terminal leader. The eggs hatch into larvae that burrow into the stem, just underneath the bark. Larvae feed on the host tree’s phloem tissue, wilting and eventually killing the terminal leader.
Later in the summer, the larvae pupate and the new adults emerge from underneath the bark. These new adults then drop to the ground and make their homes in the soil underneath the host tree for the winter where they live until the cycle begins again the following year.
Timing is of critical importance when managing white pine weevil. Once the damage is noticed, it is too late to reverse it. Preventative spraying in the spring (when daytime temperatures reach 50 degrees F consistently) to target adults before they lay their eggs is very effective. Soil treatments with systemic insecticides also work but should be timed so that the tree has time to draw up the insecticide into its tissues. Infested leaders need to be pruned out and destroyed. A new leader from one of the side branches can be staked into its place. Trees that have been infested with white pine weevil and trees close to those that have been infested should be treated yearly to end the cycle.
Keeping the trees on your property healthy with routine maintenance and inspection will help them to resist white pine weevil infestation. Healthy trees will recover faster if they do get attacked.
Our garden center staff can help you select the correct preventative treatment for white pine weevil or let our professionals do the work for you! Our certified and experienced tree care team can help.
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