American elm scale

Taxonomic classification: The American elm scale (Chionaspis americana) is a member of the order Hemiptera and the family Diaspididae. It is a specialized scale insect that infests the bark of woody plants, living underneath a protective waxy cover that protects it from environmental stressors and many predators.

Host plants: This pest primarily targets trees within the genus Ulmus (elms). While it is most commonly associated with American elm species, it can occasionally be found on other deciduous trees in urban landscapes, parks, and nurseries where dense plantings allow for rapid colonization.

Biology and life cycle: The insect typically overwinters as an inseminated female beneath the protective scale. In the spring, after the sap begins to flow, the female produces eggs. These hatch into mobile nymphs, commonly called "crawlers," which emerge from under the scale, migrate to new areas of the tree, settle down, and insert their mouthparts to feed, eventually forming their own protective covers.

Damage symptoms: The primary damage is caused by the nymphs and females feeding on the tree's phloem, which depletes essential nutrients and water. Heavy infestations result in bark cracking, premature yellowing and dropping of leaves, stunted branch growth, and general crown decline. In severe cases, large portions of the tree may experience branch dieback or total death.

Control measures: Effective management relies on a combination of cultural and chemical tactics. Pruning infested branches is a key sanitation step. Chemical control is most successful when timed with the "crawler" emergence stage, as this is when the insect lacks a fully developed protective shield and is highly susceptible to contact and systemic insecticides.

• Regular monitoring of bark for white scale encrustations.
• Application of horticultural oils during the dormant or crawler phase.
• Targeted insecticide treatments specifically during the crawler emergence period.