Lecanium scale

Lecanium scales appear as small, dome-shaped, brownish bumps on the twigs and branches of numerous ornamental and fruit trees in Western Washington. The female scales are immobile, shell-like structures that do not look like living insects until you examine them closely. Heavy infestations coat twigs with these bumps and produce copious honeydew that attracts ants and supports sooty mold.

Apply dormant oil in late winter or early spring before scale eggs hatch to smother overwintering females and eggs. For active-season populations, horticultural oil targets the crawler stage emerging in mid to late spring. Prune out severely infested branches. For high-value trees, a second oil application in early summer targets new generations; timing to crawler emergence is critical.