Scale & Mealy Bugs on Gardenias

Large and fragrant, gardenia blooms were once favored for corsages.

Large and fragrant, gardenia blooms were once favored for corsages.

Gardenias (Gardenia augusta) produce abundant white blooms up to 5 inches across, making them an amazing stand-out in the landscape. These dark green plants with their fragrant blooms are a favorite of many gardeners, who sometimes use the largest cultivars as living screens. When scale insects and mealybugs threaten to defoliate these magnificent plants, the home gardener must take action.

Scales and Mealybugs

Scales and mealybugs are both sap-sucking insects with specialized mouth parts that pierce the surface of plant tissues so the insect can reach the liquid inside. Scale insects stop moving once they begin feeding, whereas mealybugs move very slowly, but both can appear to be abnormal growths on a gardenia if you don't look too closely. Gardenias are attractive to a wide variety of scale insects and mealybugs -- strictly speaking, specific identification is unnecessary since treatment is the same for each.


Mealybugs and scales in number cause premature leaf wilt or drop due to stress on the plant. These insects also secret a sticky substance called honeydew that attracts ants and grows black sooty mold, which can interfere with photosynthesis. High populations can decrease plant vitality to the point that an already stressed gardenia will die from the feeding activity.

Non-Chemical Control

Small numbers of scale or mealybug can be hand-picked from young gardenia. A blast of water from a garden hose can also dislodge these insects -- they move too slowly to reattach before they starve. If ants are tending the scales or mealybugs, they should be lured away with ant bait so that predatory insects can move in to destroy the troublesome sap-suckers. Feeding and watering a gardenia properly will increase its vigor so it can withstand scale and mealybug attacks long enough for predators to eliminate the trouble insects.

Chemical Control

Systemic insecticides should be applied if scales or mealybugs are causing significant stress to the gardenias. Apply imidacloprid in late winter or early spring to control most of these insects (armored scale and cottony cushion scale seem to be resistant), then water the plant thoroughly. to encourage it to take in as much insecticide as possible. Insecticidal soaps or horticultural oils are extremely effective if used during the late spring when crawlers (young scale and mealybugs) are just emerging.

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