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Obscure Scale Diagnostic Guide

Melanaspis obscura

Obscure scale, Melanaspis obscura, is a serious pest of landscape oaks, but also attacks a wide variety of other hosts. This armored scale drains the sap from plants with their long thread-like mouthparts. This feeding of the sap can weaken infested trees causing premature leaf drop and die-back. Infestations are rarely fatal, but it can decrease the aesthetic value of the tree, as well as increase susceptibility to secondary infestations by other insects and diseases that could be fatal.

Trees at Risk

Landscape oaks, especially pin oaks, and red oaks in urban areas are at risk. This pest also attacks chestnuts, pecan and other hickories, beech, dogwood, maple, and willow.

Birch

Hickory

Maple

Oak

Signs of Damage

  • Premature leaf drop and dieback.
  • Sunken areas on bark creating a rough appearance.
  • Branches appear to have small silver flakes sprinkled on them.
  • Under severe infestations, the trunk or branches may be disfigured.
Obscure Scale

John A. Weidhass, Virginia Polytechnic Institute and State University, Bugwood.org

Physical Appearance

  • The protective covering on this scale is circular in shape, somewhat convex, about 3mm in diameter, and dirty gray with an occasional small black cap near the center.
  • Patches of scale several layers deep that create rough encrusted areas on bark.
Obscure Scale

Bugwood.org

Biology

  • Adult females mature by early May.
  • Adult males mature by late May.
  • Males emerge from their waxy covering to mate with females, before dying.
  • Nymphs overwinter.
  • Crawlers found mid-July through September.
  • One generation per year.

Treatment Strategy

Obscure scale is very difficult to manage after populations have established. Early detection is critical for best management of infested trees. Monitor three to four year old twigs for the gray protective covers of this armored scale insect. Multiple applications of Distance™ may be needed because of the extended egg laying period.  Heavily infested branches should be pruned and destroyed.

  • Foliar Spray using Distance

    Dosage: 8-12 oz/100 gallons water
    Timing: During summer apply Distance™ + Hort. Oil as crawlers emerge in July. Mobile crawlers appear on pin oak in early July, but they are not found on white oak for another four weeks.
    Re-Treatment: Reapply Distance™ + Hort. Oil if persists after 14 days
    Distance
    Distance
    $269.00
  • Foliar Spray using RTSA Horticultural Oil

    Dosage: 0.5-1%100 gallons water
    Timing: During summer apply Distance™ + Hort. Oil as crawlers emerge in July. Mobile crawlers appear on pin oak in early July, but they are not found on white oak for another four weeks.
    Re-Treatment: Reapply Distance™ + Hort. Oil if persists after 14 days
    RTSA Horticultural Oil
    RTSA Horticultural Oil
    $39.00
  • Systemic Bark Spray using Transtect

    Dosage: 6 packets/gallon
    Timing: Spring
    Re-Treatment: Annually
    Transtect
    Transtect
    $326.00
  • Systemic Bark Spray using RTSA Horticultural Oil

    Notes: Winter/Dormant
    Dosage: 2.5-4 oz/gallon water
    Timing: Apply during dormancy to control immatures and eggs covered by females.
    RTSA Horticultural Oil
    RTSA Horticultural Oil
    $39.00
  • Systemic Bark Spray using RTSA Horticultural Oil

    Notes: Summer
    Dosage: 1-2.5 oz/gallon water
    Timing: Apply as crawlers emerge in July. Mobile crawlers appear on pin oak in early July, but they are not found on white oak for another four weeks.
    RTSA Horticultural Oil
    RTSA Horticultural Oil
    $39.00
  • Foliar Spray using Up-Star Gold

    Dosage: 1.7 oz/100 gallons water
    Timing: Apply as crawlers emerge in July. Mobile crawlers appear on pin oak in early July, but they are not found on white oak for another four weeks.
    Re-Treatment: Multiple applications of Up Star Gold may be needed because of the extended egg laying period.
    Up-Star Gold
    Up-Star Gold
    $33.33
  • Foliar Spray using Distance

    Notes: Combined with RTSA Horticultural Oil
    Dosage: 8-12 oz/100 gallons water
    Timing: During summer apply Distance + Hort. Oil as crawlers emerge in July. Mobile crawlers appear on pin oak in early July, but they are not found on white oak for another four weeks.
    Re-Treatment: Reapply Distance + Hort. Oil if only during crawler stage
    Distance
    Distance
    $269.00
  • Foliar Spray using RTSA Horticultural Oil

    Notes: Combined with Distance
    Dosage: 0.5-1%/100 gallons water
    Timing: During summer apply Distance + Hort. Oil as crawlers emerge in July. Mobile crawlers appear on pin oak in early July, but they are not found on white oak for another four weeks.
    Re-Treatment: Reapply Distance + Hort. Oil if only during crawler stage
    RTSA Horticultural Oil
    RTSA Horticultural Oil
    $39.00

Treatment Expectations

Treatment with foliar sprays at crawler stage is critical for success.

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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