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
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
Photos of scale by Baldo Villegas