Scale insects are among the most destructive pests on ornamental plants, according to the University of Florida Cooperative Extension Program. The scale group of bugs includes many species, grouped as armored, soft and mealybug. Scale insects suck moisture from most parts of plants, although they tend to favor foliage and are particularly attracted to hibiscus, camellia and holly. Symptoms of a scale infestation range from small yellow spots on the leaves to complete die-back of entire branches. The newly hatched nymphs cause the most damage and control of them is challenging.
Watch the plant for evidence of crawlers. These are newly hatched scales. The best way to monitor the plant is by using sticky cards. You can also wrap double-sided tape around a stick, poke it into the soil and inspect the insects that become stuck to it. You may need a magnifying glass to look for the nymphs. They are identical to the adult, only smaller. The horticultural oil is best applied when the nymphs hatch and begin crawling.
Cut off all infested parts of the plant and dispose of them.
Spray the plants, including the undersides of leaves, with horticultural oil, until the insecticide drips from the plant.
Place the sticky card back into the plant and check for new pest activity. You may need to apply horticultural oil again.