Striped Pine Scale on Scotch Pine twig.
Striped Pine Scale With Bee Feeding on "Honeydew" excreted by Scale
Scale
Scale insects on trees fall into the soft and hard (armored) scale categories. Long term infestations are very damaging to tree health. They are difficult to control without pesticides, but not impossible.
European Elm Scale- Siberian Elm and American Elms
Striped Pine Scale- Scotch Pine
Oystershell Scale- Aspen
Kermes Scale- Red Oak
Cottony Maple scale- Maple
Juniper Scale- Junipers (on the needles)
Pine Needle Scale- Pinion Pines (on the needles)
Scale is typically found on the trunks, limbs and smaller twigs of plants. They are also found on the needles of some coniferous plants (Juniper Scale). They look like barnacles or oyster clusters and are usually found in great numbers. When rubbed with the hand they will smear and "bleed". A black chalky substance called Sooty Mold is often found where scale has been present for years. Sooty Mold grows on the sticky excretion released from the scale that covers any surface under the critters (Notice the black sooty mold covering the base of the needles in the photos to the right, click to enlarge). It will appear as a shadow and generally covers the entire area directly under the canopy of the tree.
Scales overwinter under the protection of their "shell". They leave this shelter during their crawler stage in the spring when they move to new locations on the host plant where they secrete a waxy substance that is the "scale" and begin feeding on the plant by piercing and sucking through the epidermis and extracting nutrients.
Common effects of severe infestations include: Twig and branch dieback. Epicormic sprouting (sucker growth)
Conventional: The most effective treatment is a systemic insecticide called imidicloprid. Because the scale are under their shell they are well protected from most methods of control. Systemic treatments act through the vascular system of the plants themselves and become available to feeding insects in the cells where they feast.
Organic: not organic but non-toxic: Dormant Oils reduce populations by killing the insects during the crawler stage and overwintering stage of their life cycle.
Cultural Practices: Proper watering. Annual soil treatments. Power washing or otherwise physically removing them from the plant.