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Lecanium Scale Diagnostic Guide

Parthenolecanium spp.

Lecanium scales are common insect pests that infest a wide range of species. There are approximately one dozen different species of these soft scales that are difficult to distinguish from one another visually. Fortunately, life history and management of these species are quite similar to each other. Lecanium scales suck sap out of the leaves and twigs, and the honeydew they excrete often becomes covered with sooty mold.

Trees at Risk

Lecanium scales may be found on a wide range of trees including, but not limited to, oaks, maples, linden, and birch. Different species of lecanium scales show preference for different host species.

Paper Birch

Linden

Silver Maple

Willow Oak

Signs of Damage

  • Dead twig tips.
  • Stunted plant development.
  • Premature leaf drop.
  • Sooty mold from excreted honeydew.
  • Presence of ants, bees and wasps.
Lecanium Scale signs

James Johnson, Georgia Forestry Commission, Bugwood.org

Physical Appearance

  • Adult females have a hemispherical body that is approximately 1/8”-1/6” in diameter.
  • Settled adults are brown in color, often with a shiny outer surface.
  • Most frequently seen adhered to small twigs – may be found there in abundance.
  • Crawlers may be found migrating to undersides of leaves in early summer.
Lecanium Scale signs

Haruta Ovidiu, University of Oradea, Bugwood.org

Lecanium Scale signs

Eric R. Day, Virginia Polytechnic Institute and State University Bugwood.org

Biology

  • Lecanium scales overwinter on twigs and branches in an immature/nymphal stage.
  • In the spring they continue development, and mature females produce large numbers of eggs.
  • Crawlers emerge in late spring/early summer and migrate to the undersides of leaves where they feed until late summer.
  • They move back to the twigs where they overwinter.
  • There is one generation per year.

Treatment Strategy

Monitor host plants for the presence of adults, crawlers, and honeydew during the season. Xytect™ and Transtect™ soil applications must be timed to ensure high insecticide levels are within the tree at the time of the first generation crawler hatch and feeding. When infestation reaches an undesirable level the primary goal is to control the crawler stage of the insect’s life cycle using foliar sprays. Crawlers are most active in the early summer, and are very susceptible to insecticide control. Once settled on leaves or twigs, they secrete a waxy covering that provides protection, so timing of sprays is important.

*NOTE: Do not apply Xytect 2F in the state of Oregon, by any application method, to linden, basswood or other Tilia species.

  • Soil Application using Xytect 2F

    Dosage: 6ml/inch of DBH
    Timing: Xytect™* should be applied in late summer/early fall of the previous year to control next year’s crawlers. Spring soil applications of Xytect™ may provide acceptable levels of control if applied early enough in the growing season.
    Re-Treatment: Annually
    Xytect 2F
    Xytect 2F
    $69.60
  • Soil Application using Transtect

    Dosage: 1 packet/5 inches of DBH
    Timing: Transtect™ can be applied to the soil in early spring to kill current year crawlers
    Re-Treatment: Annually
    Transtect
    Transtect
    $326.00
  • Foliar Spray using RTSA Horticultural Oil

    Dosage: Dormant: 2.5-4oz/gal Summer: 1-2.5oz/gal
    Timing: Apply as a dormant spray to smother second instars overwintering on twigs. Apply dormant oil to trunk and branches in spring before leaves emerge.
    Re-Treatment: As needed
    RTSA Horticultural Oil
    RTSA Horticultural Oil
    $39.00

Treatment Expectations

  • Xytect™ and Transtect™ will provide a high level of control of all soft scales. Use foliar sprays for immediate activity against crawlers or for management of overwintering females on twigs with dormant sprays. Properly timed soil applications of Xytect™ or Transtect™ will work extremely well for most soft scales.
  • Females grow rapidly in spring and produce 1,000 to 5,000 eggs. Eggs hatch in April and May and crawlers migrate to the leaves where they feed until late summer. The nymphs molt and overwinter as second instars on dormant twigs making dormant oil applications a good option, especially if soil applications of Xytect or Transtect have not been previously applied.

A Diagnostic Guide is designed to help you identify a pest issue and management solutions. Always refer to product label for all rates and approved uses. Some images courtesy forestryimages.org. Use of the images does not imply endorsement of treatments by forestryimages.org

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