Gardenias often suffer from insect infestations that can damage their health and appearance. Mealybugs are a common gardenia pest and look like white, oval-shaped spots on infested plants. Mealybugs are very small, covered in white wax, and are usually found on the stems of gardenias or the undersides of leaves.
Mealybugs are very small, measuring about 1/10 inch in length. This bug is flat and related to aphids and scale insects. Mealybugs received their name because the white waxy coating on their backs resembles ground meal. Mealybugs cause injuries to gardenia leaves from feeding on them with their sharp mouth parts that they use to pierce plant leaves and suck out plant sap.
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While there are over 275 different species of mealybugs in the United States, according to Iowa State University, only two species are common pests. The longtailed mealybug received its name for the long tail of wax that extends from its body. The citrus mealybug is a serious pest of ornamental plants and shrubs. This pest multiplies rapidly, producing a large amount of eggs during its short lifespan.
Mealybugs injure gardenias through feeding, causing the green leaves to appear stippled and distorted. Gardenia leaves may also turn yellow and drop from the plant prematurely. Gardenias infested with mealybugs often develop a condition known as sooty mold or gray sooty mold. This condition causes a gray or black coating of fungus to develop on gardenia leaves, flowers and stems. Sooty mold is the direct result of insect infestations. Mealybugs produce honeydew when feeding on plant sap, which is very sticky. Sooty mold fungi adhere to honeydew and the fungus grows on the gardenia's surface. While sooty mold is not usually harmful to gardenias, it is unattractive and a sign of heavy insect infestation.
Mealybugs are often eliminated by spraying your gardenia with a forceful stream of water from the garden hose, several times each week. This knocks mealybugs from the leaves and stems of gardenias, reducing their population. Another way to eliminate small numbers of mealybugs is to dab your gardenia with an alcohol-soaked cotton swab and remove the insects. Heavy mealybug infestations on your gardenia may warrant the use of insecticidal soaps. Wash your gardenia with this product and rinse the residue away. Horticultural oils are another way to reduce insects and remove sooty mold fungi. Oil products work on contact to smother mealybugs and loosen sooty mold, making it easier to remove.