This common scale (Coccus hesperidum) attacks a wide range of houseplants, including anthuriums, citrus, dieffenbachia, ferns, orchids, and ornamental figs. The insects' small size, immobility, and close resemblance to bark or buds mean that they often become well established before their presence is noticed, making them one of the most destructive of houseplant pests.
BIOLOGY: Female brown soft scales are 3/16 of an inch long and yellow to brown, depending on age. They are ovoviviparous (giving birth to live young). Males are rarely seen. The 1/16-inch-long, colorless to yellowish, pancake-shaped crawlers, or nymphs, are active for two to four weeks before settling down and feeding to complete their development. Once secured to a leaf or twig, they produce a waxy covering and never move again. Like many sucking insects, brown soft scales excrete honeydew, a sweet, sticky liquid. They mature in about 60 days. In houses or greenhouses, there are up to seven generations per year.
SYMPTOMS: The first indication of a problem is often shiny and sticky leaves onto which honeydew has dripped. This honeydew, in turn, is often colonized by sooty mold fungi, creating a black coating. The leaves on which the scales are actually feeding will eventually turn yellow and drop. The scales themselves appear as yellowish-brown bumps on stems, leaves, petioles, and occasionally fruit. Dislodging the hard shell with a pin will reveal legs and antennae on the underside.
CONTROL: Soft scales are difficult to control. Adults can sometimes be picked off by hand or with a pair of tweezers. Small populations can be killed with a cotton-tipped swab dipped in rubbing alcohol. Heavily infested branches are usually best pruned off. Pesticides are most effective on the crawler stage. Horticultural oils, insecticidal soaps, and pyrethrin products are recommended for houseplants and should be thoroughly applied to both surfaces of the leaves and the twigs and branches. Severely infested plants should be discarded.
From Horticulture Magazine