Olive Scale

Olive scale is an armored scale and like all armored scales, resembles a small encrustation on the plant. The adult female scale is about 0.10 (2.5 mm) inch long, with a grayish, oval, waxy covering. The male scale is more elongate with a black spot at one end. If the coverings are removed, the scale bodies of both sexes are reddish purple. Olive scale feeds on twigs, leaves, and fruits. However, it is most often noticed at harvest; dark purple spots occur on otherwise green to yellowish fruit where the scale has settled. There are several generations a year.

Early in the growing season (late May and June) first brood olive scale feed on and consequently deform young, rapidly growing fruit. A later brood, in July and August, causes the pronounced purple spotting of green fruit, rendering it worthless for most markets except perhaps black ripe process. Heavy olive scale infestations will also occur on branches, twigs, and leaves. Such infestations substantially reduce the productivity of a tree.

Olive scale can be effectively controlled by natural enemies and does not usually cause economic damage. Preserve natural enemies by selecting insecticides for other pests that do not kill beneficial insects. Control ants in the orchard because they disrupt biological control (for more information, see ANTS).

Olive scale is effectively controlled by two parasites Aphytis maculicornis and Coccophagoides utilis. Where insecticides such as carbamates (IRAC Group 1A), organophosphates (1B), and pyrethroids (3) are used, biological control will be disrupted. Be sure to monitor scale populations if disruptive insecticides are used.

Biological control and certain oil sprays are acceptable to use in an organically certified crop.

If olive scale was detected in the previous season or if disruptive chemicals are used in the orchard or on nearby crops, watch closely to detect crawlers moving onto fruit in spring and summer. Double-sided sticky tape can be applied to branches to help detect the presence of crawlers. If treatments are needed, control the first brood in late May and June or the second brood in late July and August. Apply first brood treatment when scale crawlers are seen moving on to the fruit. Treating scales in early July, between broods, is not recommended. A postharvest treatment is also effective. One of these treatments is usually all that is needed.