Calico scale, Eulecanium cerasorum, is a pest of variety woody plants. Introduced into the San Francisco area in the early 1900’s, it has continued to spread throughout the Pacific Coast states and several eastern states, including Pennsylvania, Maryland, Delaware, Virginia, and Long Island. Calico scales produce large amounts of honeydew in the spring which can coat tree leaves, branches, sidewalks, and cars, This sticky sap soon turns black from sooty mold fungi growing on it and in severe cases may interfere with the trees ability to photosynthesize, making it more susceptible to woodborers, drought, and other stresses.
Transtect soil applications or basal systemic bark sprays can be applied in spring and early summer. Xytect 10% or Transtect Infusible can be used tree injection treatments for trees that cannot be treated with foliar sprays or other systemic options. Distance can be used beginning at crawler emergence starting at 400-1200 GDD.
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 moisturelevels 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.
Transtect will provide a high level of control of all soft scales. The only reason arborists should apply foliar sprays is for immediate activity vs. crawlers. Properly timed applications of Transtect will work extremely well for most soft scales.
For heavy infestations, in the first year a combination approach of a systemic application of Transtect 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.
Signs of Damage
- Large amounts of honeydew in the spring
- Sooty mold fungi growing on the honeydew
- Stunted, yellowing leaves leading to premature leaf drop and dieback
- Large dark brown and white globular scale about ¼’ in diameter on twigs and branches in May and June
- Presence of white crawlers on the underside of leaves during summer
Photo: University of KY
Trees At Risk
- Calico scale can be a pest to all stone fruit and ornamental fruit trees, elm, maple, zelkova, honeylocust,, sweetgum, magnolia, pyracantha, dogwood, buckeye, Boston ivy, and tuliptree.
- In late winter to early spring the crawlers molt to the third instar.
- The nymphs move to the leaves to feed along the leaf veins before maturing to adults.
- In mid spring, the females continue to feed, producing eggs beneath them, and eventually turning brown and crusty.
- After egg hatch occurs in late spring (400-1200 GDD), crawlers move to the leaves and settle to feed for the summer months.
- By late summer, the crawlers move back to the woody tissue where they molt to the second instar, which is black and has a harder waxy coating.
- One generation per year.
University of Tennessee
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.