Pine bark adelgid (Pineus strobi) is an aphid like insect that feeds on the plant juices of white pines and occasionally Scotch and Australian pines. You are not likely to see the insect itself but rather the white cottony wax the insect covers itself with. Heavily infested tree trunks and branches can look white washed. Adelgids are native to Europe but widely occur throughout North America. In Canada they are mostly found in British Columbia and Eastern Canada.
Identification and Damage
Pine bark adelgids are tiny purplish insects that are less than1mm in length (1⁄32″). They may be winged or non-winged. The female adelgids cover themselves and their eggs in a white cottony wax. Look for them on the trunk, branches and at the base of needles. The eggs are light brown and laid close to the female. Damage includes shoot and branch injury. Entire branches may die back with heavy feeding. Typically a mature healthy tree can manage the feeding damage but newly planted trees and trees weakened by other stressors such as drought or root damage etc. are at greater risk.
Life Cycle of Pine Bark Adelgid
Pine bark adelgid typically over winter as immature, wingless females; although they can over winter at any stage of development. In the spring they begin feeding and and cover themselves in a white cottony wax for protection from predators. They mature to adults around April or May then lay their eggs (about 25) and die shortly after. The eggs hatch into nymphs which begin feeding on the host plant or can be blown to other nearby pines. These nymphs mature into either winged or wingless adults. The wingless ones settle in on the host plant and remain stationary the duration of their life. The winged adelgid either remain on the host or fly to another near by white pine or sometimes as scotch or Australian pine. There can be as many as 5 generations per year and all stages of development can be present at the same time.
Control and Management of Pine Bark Adelgid
Beneficial insects: Populations can vary considerably from year to year. Encouraging beneficial predators such as dusty wings, hoverflies, and lady beetles may be enough to control small populations.
Dormant oil: applied in early spring, before bud break, will kill overwintering nymphs. Heavily spray the trunk and branches. Temperatures must be at least 5 degrees C or greater with no rain in the forecast for 24 hours.
Insecticidal soap: may be sprayed in mid-April to May while the nymphs are crawling. Heavily spray the trunk and branches until dripping, with a forceful sprayer. Since there is more than one generation per year this spray may need to be repeated several times. Do not apply on hot days or when the sun is shining brightly on the foliage. Early morning is usually the ideal time to spray.
Chemicals: For very heavy infestations in regions permitted chemicals an insecticide labeled for use against pine bark adelgid, such as malathion, diazinon, endosulfan, or dimethoat may be applied according to manufacturers instructions.
Photo Credits: all photos by the author.
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