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

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

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