- Whiteflies are tiny sucking insect pests that grow 1/10 to 1/16 inch long. They have pale yellow bodies covered in a white waxy powder and white wings. When disturbed, whiteflies immediately take flight from the host plant but resettle once the danger is over. Adult whiteflies lay eggs on the underside of leaves that hatch into nymphs. The nymphs go through four stages of development until they become adult whiteflies. The insect at each stage saps essential fluid from the foliage and secretes honeydew, a sticky substance that promotes the growth of sooty mold. Whitefly infestations cause gardenia leaves to appear yellow, wilt and drop prematurely. Spray infestations with neem oil or an insecticidal soap. Alternatively, spray a registered insecticide containing acephate, cyfluthrin or imidacloprid to control large infestations.
- Similar to whiteflies, aphids are sucking insects that sap essential juices from the foliage of a gardenia plant. Measuring less than 1/8 inch in length, the insects appear in a range of colors including green, black and yellow. Unlike whiteflies, aphid infestations do not respond immediately to sudden movement. Although a few aphids cause only aesthetic damage, large infestations cause malformed or yellowing foliage, leaf loss, bloom drop and galls. Release natural predators such as ladybugs for a biological control against aphids, or spray infestations with neem oil or a low-toxicity insecticide.
- Different types of soft scale insects and armored scales feed on gardenia plants. They pierce through stems, leaves and branches and suck essential sap, resulting in stunted plant growth and yellowing leaves. Soft-bodied scales also secrete honeydew on infested leaves, thus increasing chances of sooty mold fungus that inhibits photosynthesis. Introduce parasitic wasps and ladybird beetles for biological control against scale insects. Alternatively, apply horticultural oil to suffocate and kill the insects.
- Different species of thrips, including flower and Western flower thrips, damage gardenias. Visible only under a magnifying glass, these insects are commonly found on leaves and between petals. Adults and nymphs scrape leaf surface to suck sap. While light infestations cause leaves to appear streaked, heavy infestations cause stunted flowers and yellow leaves that drop prematurely. To treat thrips, apply a foliar systemic insecticide spray containing cyfluthrin, permethrin or spinosad on infected parts of the gardenia plant every seven to 10 days.
- Other insect pests that damage gardenias include mealybugs, root nematodes and spider mites. Although chemical formulations to control the different types of insects are readily available, use organic control options whenever possible. Because healthy gardenias are less likely to become infested with insects, adopt good cultural practices so they withstand pests on their own.