Most pine trees suffer from the much the same insect problems, whether they are dwarf pine trees or not. Popular dwarf pines, such as mugo pines (Pinus mugo), hardy in U.S. Department of Agriculture plant hardiness zones 2 through 7, or Siberian dwarf pines (Pinus pumila), hardy in USDA zones 4 through 7, grace many landscapes within their growing zones, and most are relatively trouble free. Occasionally, they may become infested by insects enough to require treatment with insecticides or other controls. Always use insecticides with caution and follow all label instructions.
Some pine insects feed exclusively on the fleshy needles. The pine sawfly is first observed as masses of spotted caterpillars and causes rapid defoliation. Controls include removing caterpillars, or horticultural oil or insecticidal soap sprays at rates recommended on their labels. The pine needleminer feeds inside needles, causing them to yellow and die. Control them using contact spray insecticides such as those containing permethrin, which is found under several brand names and concentrations, when you see the adults emerge, or apply a systemic insecticide such as those containing imidacloprid, available as a liquid, granules, or dust, to the roots so the tree can take it up into its system and fight the infestation.
Trunk and Bark Insects
Bark beetles bore into the trunks of dwarf pines, making small holes. Zimmerman pine moths also bore into the trunks, leaving popcorn-like pitch masses near the entry holes. Both feed on the plant juices flowing just under the bark. There is little that can be done once the larvae are feeding inside the tree. If larvae are visible, usually around April or August, sometimes drenching the bark with sprays containing permethrin is effective. Permethrin is found under a number of brand names and its concentrations differ; apply according to label directions.
Certain insects prefer the new shoots or leaders (usually the tallest part of the tree) of dwarf pine trees. Some dwarf pine trees may have no leader. European pine shoot moths are often found on pine shoots in May. They eat small buds, causing them not to open in spring. Pesticides are only effective when caterpillars are moving to new shoots. Pine weevils feed on the sapwood of the leader branches, causing distortion and death. They leave behind white drops of resin. Control by pruning out infested leaders in July.
Twig and Branch Insects
Scale insects may infest dwarf pines. Pine tortoise scale are insects that hide under brown, helmet-like coverings with spots or patterns on the back, and striped pine scale has a similar appearance. If the infestation is light, trim infected branches or remove scale by hand. Horticultural oil sprays applied when the scale infestation is overwintering may be successful. Insecticides that act systemically, such at imidacloprid, which comes in various forms and concentrations, may provide long-term control. It's applied directly to the roots, which transport the insecticide throughout the tree.
- Forest Service Department of Agriculture: Pinus Mugo
- Missouri Botanical Garden: Pinus Pumila "Compacta"
- Washington State University: Dwarf Conifers
- U.S. Forest Service: Pinus Banksiana
- Iowa State University Extension: European Pine Sawfly, an Early Season Pest
- Colorado State University: Leafmining Insects
- University of California Agriculture and Natural Resources: Bark Beetles
- Colorado State University: Zimmerman Pine Moth
- Ohio State University: European Pine Shoot Moth
- University of Minnesota: Pine Tortoise Scale
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