Marin Rose Society

FAST FACTS - SCALE
by Nanette Londeree, Master Rosarian

SIGNS

Small, grayish to white, round to oval encrustations on canes, ranging in size from 1/8 to 1/4 inch (armored scale)

Orange, yellow, or brown elongated, fluted, white cottony egg sac attached to body (soft scale)

SYMPTOMS

Scale

Darkening of cane

Decline of plant health and vigor

Dieback of twigs or stems

Honeydew on leaves, canes; sticky, sooty mold on leaves and ants (soft scale only)

CAUSE

Armored scales, Aulacaspis rosae (rose scale) and Quadraspidiotus perniciosus (San Jose scale)

Soft scale (cottony cushion scale), Icerya purchase

OPTIMAL CONDITIONS

Roses that are not heavily pruned each year

Nut and stone fruit trees infected with the pest in the area; spread by wind from almond orchards (San Jose scale)

Cottony cushion scale on citrus, nandina, and pittosporum in the area

TREATMENT

Prevention:

Provide good growing conditions and cultural care to help roses be more resistant to scale

Monitor susceptible varieties of plants for infection and treat immediately

Maintain good garden sanitation, and dispose of any infected plant materials

Control ants

Limit use of insecticides that may harm beneficial insects

Garden to encourage natural enemies (parasitic wasps and flies; the vedalia beetle, Rodolia cardinalis

Elimination:

Prune away and destroy infected canes

Apply horticultural oil spray after pruning in the winter; repeat spraying may be necessary

GOOD GUY / BAD GUY?

Can be a bad guy if infestation is severe

The photos of Scale are by Baldo Villegas from the extraordinary website: http://members.tripod.com/buggyrose/irosepests.htm

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