Black Dots on Garden Leaves: Scale Insects, Treat with Horticultural Oil

An NYC gardener with a crowded 2nd-floor garden (roses, honeysuckle, blueberries, lilacs, silverlace, climbing hydrangea, morning glories) saw raised, hard black dots on most leaves last summer, devastating hydrangea, eating lilac/silverlace leaves. Roses and honeysuckle unaffected. Asked for ID and preventive spray.

Identification and Treatment

Tom identified scale insects (protective hard shell). Horticultural oil spray controls them, but only effective before shell forms. Can be used preventively. He linked to an example product (Monterey Saf-T-Side) and suggested asking a trusted nursery.

Scale insects appear as hard bumps; horticultural oil works on crawlers; preventive spraying helps.