Obscure scale, Melanaspis obscura, is a serious pest of landscape oaks, but also attacks a wide variety of other hosts. This armored scale drains contents of cells from plants with their long thread-like mouthparts. This feeding of the cells 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.
Obscure scale is very difficult to manage after the 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. Heavy obscure scale populations will require two years of systemic soil treatments of Transtect to reduce populations.
A combination approach of a systemic Transtect treatments and a crawler stage foliar spray may be used to provide additional control of heavy initial scale populations. As scale population is reduced in following years consider applying a stand-alone soil treatment of Transtect.
Multiple applications of spray treatments of Distance and or Up Star Gold may be needed because of the extended egg laying period. Heavily infested branches should be pruned and destroyed.
Other Treatment Practices
- Promote health and vigor with proper irrigation, mulching, proper pruning and prescription based fertilization practices.
- Adequate water is a key factor in maintaining stress free plants. A slow, deep watering event once every few weeks during dry conditions will help maintain soil moisture levels and minimize stress.
- Mulch is very beneficial for all trees because it reduces competition with turf and moderates soil temperature and moisture levels. The addition of 3 inches of wood chips or shredded bark under the drip line can have a very beneficial effect by holding in moisture and promoting healthy fibrous roots.
- Cambistat can be also be used to promote tree health and reduce the incidence and severity of stress mediated diseases and insect problems on trees growing in urban areas.
- Do not over fertilize, as it can lead to increased scale populations.
Trials using Transtect as a soil/lower systemic bark spray has displayed excellent control with gloomy scale, which is closely related to obscure scale.
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
- 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 is not a pest of trees growing in the forest
Photo: John A. Weidhass
Virginia Polytechnic Institute and State University, Bugwood.org
Trees At Risk
- Landscape oaks, especially Pin oaks (Quercus palustris), and red oaks (Quercus rubrum), in urban areas
- Also attacks chestnuts (Castanea spp.), pecan, and other hickories (Carya spp.), beech, (Fagus spp.), dogwood (Cornus spp.), maple (Acer spp.), and willow (Salix spp.)
- Adult females mature by early May. Adult males mature by late May.
- Males emerge from their waxy covering to mate with females, before dying.
- Crawlers emerge in mid-late summer (1500-2500GDD) over the course of several (4-6) weeks.
Always refer to product label for rates and approved uses. Some images courtesy of forestryimages.org or Wikimedia Commons. Use of the images does not imply endorsement of treatments.