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
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 titer 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. Xytect 10%or Transtect Infusible as a tree injection treatment for trees that cannot be treated with foliar sprays or other systemic options
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.
Xytect and Transtect will provide a high level of control of all soft scales. Arborists should 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 spring 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.
Signs of Damage
Lecanium scales can cause twig dieback, stunted plant development, and premature leaf drop. The presence of sooty mold on the excreted honeydew may also give a blackened appearance to foliage and branches in severe cases. Ants, bees, and wasps may be attracted to the honeydew, and could be a cue to look for lecanium scales. The insects themselves are typically hemispherical or turtle-shaped, brown, and range in size from 3 to 12 mm in length. They can be found in abundance on small twigs of host species.
- Heavily infested trees may display dieback of branches and twigs
- Premature leaf drop may occur in late summer
- During severe stress, a heavy infestation of lecanium scales could kill an entire tree
- Heaviest damage occurs in spring and early summer
- Honeydew is excreted on twigs, branches, and leaves
- Adult females have a hemispherical body that is approximately 0.4 inches in diameter
- 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
Photo: James Johnson
Georgia Forestry Commission, Bugwood.org
Photo: Haruta Ovidiu
University of Oradea, Bugwood.org
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.
A few examples include:
- Fletcher scale–arborvitae and yew
- Terrapin scale–maples and peach
- Hickory lecanium scale–hickory and elm
- Globose scale–stone fruits
- 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(700-1645 GDD, N. Catalpa bloom)and migrate to the undersides of leaves where they feed until late summer.
- At this time they move back to the twigs where they overwinter.
- There is one generation per year.
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.