The Scale insect Parthenolecanium corni is usually known as the European fruit Lecanium and can be found throughout Southern Canada and United States. This species infests a wide range of hardwood trees including elm, oak, maple, mountain ash, white ash, beech, apple and hawthorn, as well as fruit trees. Infestations of the insect can be identified by the presence of numerous, small (3 mm), brownish, hemispherical scales on the bark of twigs and branches.
In its nymphal stage of growth, the European fruit Lecanium is spindle shaped with a smooth brownish red cover. Both the male and female of this species have the presence of a waxy cover, which on the female is a fine white powder, and the male is more transparent. The damage caused by this species will result in curling of lower leaves and yellowing, with ultimately the dropping of the leaves. The feeding of this species will also result in the formation of honeydew (sugar rich substance), which can lead to subsequent infection or colonization of the leaf surfaces. The possible infection can lead to a declined rate of photosynthesis, thus greatly affecting the overall health, yields and quality of the crop.
Scouting should take place in early June in order to get control early of any possible infestations. Examine all possible infested trees frequently to determine when crawlers (the youngest-only mobile larvae) may hatch from eggs. The application of insecticide in early spring is usually recommended to get a hold of this pest, before it takes advantage and the infestation becomes generalized in the trees. At this point, efficient control is very difficult.