Gardenia Insects & Related Pests

Prepared by J. McLeod Scott, HGIC Horticulture Extension Agent, and Joey Williamson, HGIC Horticulture Extension Agent, Clemson University. (New 08/10; Revised 08/11)

HGIC 2059

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With their wonderfully fragrant blossoms and lustrous, dark green leaves, gardenias (Gardenia angusta, previously known as G. jasminoides) are popular shrubs with many southern gardeners. Their positive qualities compensate to a large extent for the fact that gardenias are somewhat high-maintenance plants with fairly specific cultural requirements. To learn more about growing healthy gardenias, see HGIC 1065, Gardenia. In addition to problems resulting from improper growing conditions, gardenias are also susceptible to several diseases, insect pests and other problems. For information on diseases and other problems that affect gardenias, see HGIC 2058, Gardenia Diseases & Other Problems.

Insect Pests

Whiteflies: Whiteflies are not true flies, but are more closely related to scale insects, mealybugs and aphids. They are very small – about 1/10 to 1/16 inch long. They have a powdery white appearance and resemble tiny moths. When at rest, the wings are held at an angle, roof-like over the body. The immature stage is scale-like and does not move. When plants that are infested with whiteflies are disturbed, the whiteflies flutter around briefly before settling again.

Both adults and immature forms of the citrus whitefly (Dialeurodes citri) feed by sucking plant sap. The damage that they cause is similar to that caused by aphids. The infested plant may be stunted. Leaves turn yellow and die. Like aphids, whiteflies excrete honeydew, which makes leaves shiny and sticky and encourages the growth of sooty mold fungi. See Sooty Mold section in HGIC 2058, Gardenia Diseases & Other Problems for detailed information.

Whitefly adults on underside of gardenia leaf
J. McLeod Scott, ©2010 HGIC, Clemson Extension

Control: A low-technology, non-toxic method for reducing the number of whiteflies involves first brushing against an infested shrub. Then, as the adult whiteflies hover above the plant briefly, they can be vacuumed out of the air.

Insecticidal soap is effective against whiteflies, but the plant must be sprayed thoroughly so that the soap contacts the insects. If stronger insecticides become necessary, products containing pyrethrin, bifenthrin, cyfluthrin, permethrin, esfenvalerate, acephate, imidacloprid and disulfoton can be used. See Table 1 to identify products that contain these insecticides.

Scale Insects: Various scale insects feed on gardenias, including the soft scales – Japanese wax scale (Ceroplastes ceriferus) and cottony cushion scale (Icerya purchasi); and the armored scales – tea (Fiorinia theae), greedy (Hemiberlesia rapax) and oleander scales (Aspidiotus nerii).

Japanese wax scale, a soft scale that attacks gardenias is typically found on twigs and branches.
Giuseppina Pellizzari, Faculty of Agriculture, Dept. of Entomology, www.insectimages.org

Scales are unusual insects in appearance, and as a result are sometimes misidentified by gardeners either as parts of the plant itself or as disease organisms rather than insects. Adult female scales are small and immobile, with no visible legs. They secrete a waxy coat that varies significantly in shape and color depending on the species. Adult males tend to be very small and have wings which allow them to fly so they can locate females.

Cottony cushion scale, a soft scale
Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org

Scales feed on plants by piercing the leaf, stem or branch with their mouthparts and sucking sap. Their feeding can weaken or kill branches. Heavily infested gardenias are often stunted with small flowers and leaves. Leaves may yellow and drop early. Like aphids, soft scales excrete honeydew. Armored scales do not excrete honeydew. The growth of the sooty mold fungus on honeydew results in leaves that are covered in dark fungal growth. See the Sooty Mold section in HGIC 2058, Gardenia Diseases & Other Problems for detailed information.

Tea scale is an armored scale that feeds on gardenias. This scale is found mainly on the lower surfaces of leaves.
Clemson University - USDA Cooperative Extension Slide Series, www.insectimages.org

Adult scales are relatively well protected from traditional insecticides by their waxy covering. Their immature forms, called crawlers, are susceptible, however.

Control: A combination of various natural enemies, including ladybird beetles (ladybugs) and parasitic wasps, usually keep scale insects under control. With light infestations, scale can be scraped off or infested branches can be removed and destroyed. If chemical control is necessary, horticultural oils can be applied and work by suffocating the scales. In terms of traditional insecticides, only the crawler stage is susceptible. Recommended insecticides for use against crawlers include the following: permethrin, lambda cyhalothrin, cyfluthrin, bifenthrin, esfenvalerate, carbaryl and insecticidal soap. Apply these materials only when crawlers are present and repeat after 10 days.

Soil-applied insecticides can give season-long control of scale insects. Imidacloprid can control soft scales, and dinotefuran can control both soft and armored scales. These are applied as a soil drench or as granules which are watered into the soil. See Table 1 for products containing these insecticides. As with all pesticides, read and follow all label instructions and precautions.

Aphids: These small (about 1/8 inch long), soft-bodied, pear-shaped insects are sometimes referred to as plant lice. They vary in color according to species and can be shades of green, yellow, pink or black. Both the green peach aphid (Myzus persicae) and the melon (or cotton) aphid (Aphis gossypii) feed on gardenias. They are usually found in clusters on new growth of buds, leaves and stems.

Both winged and wingless adults as well as immature green peach aphids are present on a leaf. Green peach aphids infest a wide range of plants, including gardenias.
Whitney Cranshaw, Colorado State University, www.forestryimages.org

Aphids feed on plant sap with their piercing-sucking mouthparts. A low population of aphids does little damage to a gardenia; however, aphids reproduce very rapidly and can quickly reach numbers that cause damage. Their feeding results in distorted or curled and stunted growth. Heavy infestations can reduce the number and quality of blooms. As they feed, aphids excrete honeydew, a sugary substance that often attracts ants. In addition, honeydew supports the growth of unsightly, dark-colored sooty mold fungi on the leaves. See the Sooty Mold section in HGIC 2058, Gardenia Diseases & Other Problems for details.

Control: Aphids have several natural enemies, including parasitic wasps, ladybird beetles (ladybugs) and larvae, and green lacewing adults and larvae. Their natural enemies tend to keep aphid populations under control except in cool weather. Ants are sometimes present with aphid infestations and will protect them from their natural enemies. If ants are present, they should be controlled.

Aphids can be hosed off with a strong stream of water directed above and below the leaves. Spraying with water should be repeated frequently as needed, focusing in particular on new growth. Gardenias can also be sprayed with insecticidal soap or horticultural oil to control aphids. Insecticidal soap or horticultural oil must be sprayed onto the aphids to be effective. Repeat spray three times at 5-7 day intervals. Foliar injury from soaps and oils may occur on plants under drought stress. Water the plants well the day before spraying. Only apply horticultural oils or insecticidal soaps if temperatures are below 90 °F, and apply very late in the day to prevent foliar injury.

While higher toxicity insecticides are available, it is important to note that aphids are very difficult to control because they multiply so rapidly. Leaving even one aphid alive can quickly result in a population explosion. In addition, these insecticides kill the natural enemies of aphids.

If stronger insecticides are deemed necessary, the following are available in homeowner-size packaging. Sprays containing acephate, bifenthrin, cyfluthrin, permethrin, lambda cyhalothrin, esfenvalerate, malathion, neem oil, or pyrethrin will control aphids. Soil drenches or granular applications of imidacloprid, dinotefuran, or disulfoton will control aphids and last longer within the plant to prevent future infestations. See Table 1 for products containing these insecticides. 

Thrips: Flower thrips (Frankliniella tritici), Western flower thrips (F. occidentalis) and various other thrips species are pests of gardenia flowers. Thrips are slender, dark-colored insects, with fringed wings. Adults are less than 1/16 inch in length. To see these fast-moving pests, you need a magnifying lens. Thrips are typically found on leaves and between flower petals. Both adults and nymphs (immature insect stages that resemble the adult, but are smaller) feed by scraping surface cells to suck plant sap.

When thrips feed on flower buds, the flower may die without opening. With a light infestation, their feeding causes leaves to have silvery speckles or streaks. With severe infestations, flowers are stunted and distorted and may turn brown and die.Thrips feed also on expanding leaves, which creates purplish red spots on the undersurfaces and causes foliage to severely curl or roll, then drop prematurely.

As a result of their small size, thrips are difficult to detect before damage is obvious. To sample for thrips on gardenia flowers, hold a sheet of stiff white paper under injured flowers, and then tap the flower. Examine the paper in bright sunlight. Any thrips present will move around on the paper. In addition, blowing lightly into the blooms causes thrips to move around, making them easier to see.

Control: Several naturally-occurring enemies feed on thrips. To avoid killing these beneficial insects which reduce thrips populations, insecticides should be avoided as much as possible. Grass and weeds in the area should be kept mowed or removed when possible.

If it becomes essential to spray an insecticide, the following are available in homeowner-size packaging: bifenthrin, cyfluthrin, lambda cyhalothrin, permethrin, esfenvalerate, or spinosad. Acephate is a foliar, systemic spray insecticide that will better control thrips that are within flower buds than contact insecticides. Spray when thrips are present and again in 7 to 10 days. Soil drenches or granular applications of dinotefuran, disulfoton or imidacloprid will give some thrips suppression. See Table 1 for specific products.

Related Pests

Spider Mites: Mites are not insects. They are more closely related to spiders, having eight legs as adults rather than six. Spider mites are extremely small (about 1/50-inch long) and are somewhat difficult to see on a plant without a magnifying lens. One way to make them easier to detect is to hold a piece of white paper under a branch and then tap the branch sharply. If still not visible, wipe your hand over the paper. If mites are present, red streaks will be seen.

Two-spotted spider mites (Tetranychus urticae) are pests on gardenias in South Carolina. While these mites may be present throughout the growing season, their populations tend to reach damaging numbers during hot, dry weather.

Mites have piercing-sucking mouthparts. They suck plant sap, typically feeding on the lower surface of a leaf. Early damage is seen as yellow or white speckling on the leaf's upper surface. The shape of new leaves may be distorted as a result of their feeding. Fine webbing may be seen on the undersides of leaves. With severe infestations, webbing may cover both sides of leaves as well as branches. Webbing can collect dust and debris and makes the plant appear untidy.

Two-spotted spider mites on a leaf
David Cappaert, Michigan State University, www.forestryimages.org

Control: Both beneficial insects, such as lacewings and lady beetles, and predatory mites prey on spider mites. Predatory mites are about the same size as spider mites but can be distinguished from spider mites by their long legs and the speed with which they move. Several species of predatory mites, lacewings and lady beetles are available commercially for use as biological control agents.

A strong spray of water is a non-chemical control option that removes eggs, larvae (six-legged immature stage), nymphs (eight-legged immature stage) and adult mites. Be sure to spray lower surfaces of leaves and repeat as needed. This method is most effective with light infestations as seen with early detection. An important advantage of this control method is that populations of natural pest enemies are not harmed.

Insecticidal soaps and horticultural oils are effective control options for spider mites and are essentially nontoxic to humans, wildlife, and pets, and only minimally toxic to beneficial predators. When using these products, good coverage is critical to ensure contact with the pest, and reapplication may be needed as determined by follow-up monitoring for the pest. Foliar injury from soaps and oils may occur on plants under drought stress. Water the plants well the day before spraying. Spray very late in the day, and do not spray with soaps or oils if the temperature exceeds 90 °F.

When growing gardenias, the use of broad-spectrum insecticides should be avoided as much as possible as these products can kill off natural enemies that help keep spider mite populations in check. Also avoid pesticides that claim to "suppress" mites as they tend to be weak miticides. When stronger chemical control is needed, the following insecticides/miticides are available in homeowner-size packaging: tau-fluvalinate or bifenthrin sprays or granular applications of disulfoton. See Table 1 for products containing these insecticides.

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