Scale & Mealy Bugs on Gardenias

Mealybugs are the most common pest found on gardenias.

Gardenias, with their dark, glossy foliage and large, fragrant flowers, are popular among gardeners, but unfortunately, they are also popular among insects. They are often grown indoors, and the confined environment encourages infestations of mealybugs and scale insects. These insects are difficult to control and can result in the death of the plant.

Detecting Insects

Mealybugs are probably the most common pest found on gardenias. They look like masses of cotton and are found where the leaves attach to the stem. Scale insects don't look like insects at all. They appear as raised brown bumps on leaves, stems and twigs. Both insects secrete a sticky substance called honeydew, which is host to the unsightly sooty mold fungus.

Infestations that are caught early are the easiest to control, so inspect gardenia bushes regularly. Once a plant is infested, the insects quickly spread to other plants, especially when grown indoors. Avoid exposing other plants by isolating infested gardenias whenever possible.

Mealybugs

A mealybug's body is about 1/4 inch long and is hidden inside a mass of filaments that give it a cottony appearance. It sucks sap from the plant through a long beak used to pierce the plant tissue. Heavily infested gardenias are weakened by the loss of sap and may die. Gardenias grown indoors, in sun rooms or in greenhouses are more susceptible to mealybugs than those grown outdoors.

Scale Insects

Like mealybugs, scale insects feed by piercing the plant tissue and sucking the sap from gardenia bushes. Leaves and stems will turn yellow and the shrub will decline. Scale insects are covered by a hard shield composed of shed skin and wax. The insect sits under this shield and remains in the same place most of its life.

Integrated Management

The best control for light infestations of mealybugs is to pick off the insects or dab them with a cotton swab saturated with alcohol to kill them. Because of their hard shell, scale insects are more difficult to kill with a contact method. The scales can be scraped off if the infestation is light, but pruning off infested parts of the shrub may be the only solution in severe infestations.

Insecticides

When a mealybug infestation is severe, use an insecticide that contains insecticidal soaps, neem, or pyrethrin. For gardenias grown indoors, choose a spray designed for houseplants and follow the instructions on the label. Scale insects are not affected by contact sprays because of their protective covering. Use a dormant oil spray in early spring to kill overwintering nymphs that have not yet formed a shell. Dormant oil sprays are only effective when every part of the plant is covered to the point where it drips from the leaves and branches.

Systemic insecticides work from within the plant to kill scale and mealybugs. Some are injected into the plant and others are used to drench the soil around the shrub. Foliar sprays are also available, but not recommended because these insecticides are toxic. In some cases, systemic insecticides are only effective against insects that are feeding on leaves.

References

• University of Florida IFAS Extension: Growing Gardenias in Florida
• Iowa State University Extension: Mealybugs Make a Meal of Your Houseplants
• Iowa State University Extension: Scale Insects on Ornamentals