Pine needle scale crawlers will be emerging soon

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

We received a sample of Mugo a week or so ago that was heavily infested with pine needle scale Chionaspis pinifolia (Hemiptera: Diaspididae). Pine needle scale is a common, sometimes serious pest of two needle pines, especially Mugo and Scotch pines. Pine needle scale feeds by sucking plant juices from the needles causing the needles to turn yellow and eventually brown. As pine needle scale numbers build, the needles become covered with the tiny, white scale insects.

The insect overwinters in the egg stage under dead female scales. Because of this dormant oils are not effective against pine needle scale and other armored scales that overwinter as eggs. There are two generations of pine needle scale in Michigan. First generation eggs hatch and the tiny crawlers emerge when lilacs begin to bloom in the spring. The second generation crawlers appear in late July.

Mugo and Scotch pines should be inspected at least twice a year for yellowing and large numbers of scales. If pine needle scale becomes numerous and the tree shows signs of stress, then control measures should be considered. The least disruptive method is to apply summer horticultural oil spray when the crawlers are active during the bloom period of common lilac. Summer oils should be applied at a concentration of 1.0 to 1.5 percent. A more aggressive strategy is to apply a spray containing Sevin, malathion or cyfluthrin (sold as Bayer Advanced Garden Insect Control for homeowners or Tempo for commercial applicators) in the spring when the first generation crawlers are hatching.

It is important to provide full coverage of the insecticide to interior portions of the tree, particularly lower branches. Two applications of a registered insecticide may be necessary to manage heavy populations as female scales have a long egg-laying period. Be sure to read and follow all the instructions and safety precautions found on the pesticide label before using any pesticide.

Pine needle scale
A small branch of Mugo pine showing a heavy
infestation of pine needle scale.
Photo by J.Byrne, Diagnostic Services.

Pine needle scale upclose
A close up a pine needle scale. The arrows
point to the
exuviae or cast skins of the
nymphal stages attached to the
white scale
covering. Photo by J. Byrne, Diagnostic Services.

Pine needle scale detached
A close up a pine needle scale with the dead female insect
separated from the white scale covering.
Photo by H.Russell, Diagnostic Services.

Pine needle crawlers
Hundreds of pine needle scale crawlers.

Photo by J. Byrne, Diagnostic Services.

Pine needle crawlers
A close up of three pine needle scale crawlers. If you look
closely you can make out the antennae and eyes.
Photo by Jan Byrne, Diagnostic Services.

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