“What will kill white pine weevils? In the spring, they bore into and kill the leader on my white pine trees.
Thank you for the email regarding White Pine Weevils (Pissodes strobi). Chemical control should be considered when 2 to 5% of the trees are weeviled in a single season. Before making the decision to reduce the weevil population, a biological and economic evaluation is highly desirable. Information such as stand stocking, non-weeviled tree height, growth rate, and stand location relative to sensitive habitats should be used in the process of decision making.
The interval between treatments depends on the level of infestation. In low or moderate weevil hazard areas, a second treatment will usually not be needed for 4 to 6 years. In high weevil hazard areas, the interval between treatments may need to be shorter. Timing of the application and optimal coverage of the terminal buds and leaders with insecticide are critical to the success of a chemical control program.
Chemical insecticides are effective only against adult weevils, because all the immature stages are spent inside the leader. Because of the short residue properties of most insecticides, it is important that applications be well synchronized with periods of peak adult activity. Chemical control measures can be undertaken either in spring (when the adults emerge from hibernation and start feeding and oviposition) or in fall (after the new adults emerge). Applications in spring can be concentrated to cover the leader and upper branches. Weevils are especially susceptible to control measures during fall when they are feeding on new growth in the upper crown. Using backpack mist-blowers or other ground equipment has been more
successful than aerial application. Chemical application in conjunction with pruning of infested leaders gives the best results.
Spray the leaders in the spring before the buds open. Make sure they are thoroughly covered. Most control operations will require 2-3 gallons of mixed spray per acre. Refer to the insecticide container label for mixing instructions. Spray all leaders each time an area is sprayed and whenever current damage approaches 10% of total number of trees. High value Christmas trees may need to be sprayed every year. Spacing and tree height will greatly influence the time necessary to spray each area. If spraying is done in the fall, add the recommended extender to the insecticide.
We currently do not sell any products that are labeled for White Pine Weevils. However, depending on the volume of trees you have to spray, there are other options available.
–For Commercial Grower Use: Diflubenzuron or oxydemeton methyl are currently registered for white pine weevil control in plantations, and require an applicator permit or license as noted below. Diflubenzuron is an insecticide which is an insect growth regulator and acts by interference with deposition of insect chitin. Efficacy of diflubenzuron against the weevil is greatly enhanced by the addition of 6-7 oz. of dormant oil (without ethion) per gallon of spray mixture. Caution: dormant oil may cause a reduction of blue color when applied to blue spruce.
–For Home Gardener Use: I recommend Bonide Borer and Miner Killer. The active ingredient is Permethrin and can also be used for birch leaf miner, flat and round headed borers, peach tree borers, bark and wood boring beetles, and taxus and strawberry root weevils. It should be found in your local garden center or hardware store or online (Google search for online sites to purchase from:
I hope this information helps you out. If you have any other questions, please feel free to ask.
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