European elm scale

The European elm scale (Gossyparia spuria) is a significant scale insect belonging to the family Eriococcidae within the order Hemiptera. It is characterized by the white, cottony or felt-like wax secretion that encircles the female during the reproductive stage. This distinctive appearance makes the infestation relatively easy to identify on the bark of host trees during the spring and summer months.

The primary hosts of this pest are species of the genus Ulmus (elm trees). While it is most commonly found on elm, it can occasionally affect other ornamental trees under specific environmental conditions. Urban landscapes and nurseries are particularly vulnerable because the pest thrives in environments where host trees are planted in close proximity, facilitating the spread of mobile crawlers.

The insect typically completes one generation per year. It overwinters as second-instar nymphs sheltered in bark crevices, pruning wounds, or branch crotches. As spring temperatures rise and sap flow begins, nymphs migrate to leaves and young twigs to feed. Adult females become sessile and produce the characteristic white egg sacs, from which the next generation of crawlers emerges in early summer.

Damage is caused by the insect extracting phloem sap, which deprives the tree of essential nutrients. Infested elms often exhibit chlorosis, stunted growth, foliage drop, and branch dieback. Furthermore, the excretion of honeydew promotes the growth of sooty mold, a dark fungal layer that covers leaves and twigs, reducing photosynthesis and leaving the tree in a weakened, unsightly state.

• Prune and destroy heavily infested branches during the dormant season.
• Apply dormant horticultural oils to smother overwintering nymphs.
• Use systemic insecticides when crawlers are active in early summer.
• Promote tree vigor through proper watering and fertilization practices.
• Encourage beneficial insects, such as lady beetles, which are natural predators.