What Do You Use to Kill Scale on Gardenias?

Symptoms of Scale

• Scales are tiny insects that infest plants. They might resemble no more than bumps on the branches of a gardenia, but these tiny insects and their larvae can do a lot of damage. The insects suck sap from the gardenia, killing leaves and twigs, and leave behind a sticky substance called honeydew, which encourages the growth of mold and infestation by ants. Ants feast on the honeydew and protect the scales, but kill off beneficial insects.

Types of Scale

• Armored scales have a hard, protective outer covering, while soft scales lack this covering. Many scales are named for their colors -- black, red, brown and calico scale, for example. Cottony cushion scales resemble rows of miniature cotton balls arrayed along the stems of the plant. These balls are the eggs sacks of the insect, also called cottony cushion scale, that infests the plant.

Biological Controls

• Scale has a number of natural, biological enemies. Sometimes known as lady bugs, lady beetles, particularly a red-and-black version known as Rodolia cardinalis, lay eggs alongside the scale eggs. The lady beetle eggs hatch first, and the larvae eat the scale eggs. The larvae of Cryptochaetum iceryae, a parasitic fly, also thrive on scale eggs. To encourage the proliferation of these natural enemies, control ants, and avoid using pesticides.

Other Controls

• If the infestation is confined to a small area, cutting off the affected branches and burning them may be enough to control the situation. Spraying plants with dormant oil can be effective in killing adult insects and keeping the eggs from hatching. The University of California-Davis Department of Agriculture and Natural Resources recommends winding double-sided tape around branches near egg sacks. When the larvae emerge, the tape will catch them, and they'll die without doing more harm to the gardenias.