How to Manage Pests

Irregular pine scale—Toumeyella pinicola

Irregular pine scale (family Coccidae) is a serious insect pest of various pines, especially Monterey pine.

Identification

Adult females are about 1/4 inch long and irregularly hemispherical with a roughened surface. The scale females and nymphs lack obvious legs or other appendages. The bodies of female adults and nymphs occur on twigs and are yellowish-white with brown and gray and sometimes pink. The scales can appear blackish when heavily covered with sooty mold that grows on the abundant honeydew they excrete.

The crawlers (mobile first instars) are flattened, oval, and orange to yellow. They can be observed on needles during late winter through spring.

Large numbers of male cocoons can be found on needles and resemble grains of rice. The cocoon is elongate oval, somewhat flattened, and has a raised central ridge extending from one end to the other. Adult males are delicate insects with one pair of wings, long antennae, and tail filaments. Adult males are easily overlooked.

Lookalikes. Monterey pine scale, Physokermes insignicola, and pine tortoise scale (PDF), Toumeyella parvicornis, also infest pines and resemble irregular pine scale. In comparison with the Toumeyella species, the Monterey pine scale is dark­er, less irregular, more spherical, and causes little or no damage. Monterey pine scale is found mostly in the San Francisco Bay Area.

Pine needle scale, Chionaspis pinifoliae, is an armored scale (family Diaspididae) that resembles the males of the three species named above. However, this species has no dark, globular individuals as with the females of the soft scales (family Coccidae) above. Pine needle scale infests all species of pines and sometimes cedar, Douglas-fir, and spruce.

Life cycle

Irregular pine scale develops through 3 life stages: egg, nymph, and adult. The scale overwinters as immature females on 1- or 2-year-old shoots, typically in colonies blackened by sooty mold and encrusted with honeydew. Females mature and produce eggs beginning in late winter. Each female can produce up to 1,000 eggs during her lifespan. The eggs hatch into mobile first instars (crawlers) during February through May in Southern California and from late April through June in the San Francisco Bay Area.

The crawlers that will become males mostly settle and begin feeding on pine needles. Crawlers that will mature into females settle and feed on young shoots. The scale has one genera­tion per year.

Damage

The scales suck and feed on pine needles and small twigs. They excrete abundant honeydew on which black sooty mold grows. Ants are attracted to feed on the honeydew and attack beneficial parasitoids (parasites) and predators that otherwise would help to control the scale. The scales themselves can become so heavily covered with blackish sooty mold that the fungal growth can completely cover the bodies of female scales.

Prolonged feeding by an abundance of irregular pine scales can virtually stop a pine's production of new shoots. Large infestations of the scale cause needles to turn yellow or brown and drop prematurely. Premature needle drop can seriously weaken trees and sometimes kill young pines.

Solutions

If the scale has been abundant and damaging, monitor for crawler emergence by wrapping several infested twigs with double-sided sticky tape traps. Inspect and replace these tape traps weekly or inspect foliage weekly with a hand lens beginning in February in Southern Cali­fornia or in April in Northern California. See the "Tape Traps" section in Pest Notes: Scales for details on using this method.

Thoroughly spray shoot terminals with horticultural oil when crawlers first become abundant and spray again about 3 weeks later. Alternatively if the trees are large or located where spray drift would be a problem, in late winter a systemic insecticide such as imidacloprid can be applied preferably by drenching the material onto soil around the base of the trunk as directed on product labels. Always be sure to read the product label and wear appropriate personal protective equipment when making applications.

Adapted from Insects Affecting Ornamental Conifers in Southern California, University of California Agriculture and Natural Resources, and Pests of Landscape Trees and Shrubs: An Integrated Pest Management Guide, University of California Integrated Pest Management Program (UC IPM).

Adult females of irregular pine scale.

Cocoons of male irregular pine scale.

Irregular pine scale male cocoons on needles and adult females on the twig.