Scales can ravage entire populations of gardenias (Gardenia jasminoides), which grow in U.S. Department of Agriculture plant hardiness zones 8 through 11. They suck the essential nutrients from the soft, green parts of the plant and leave behind wounds, excretion and carcasses that can attract mold and fungus. Fortunately, several natural and man-made control methods are available that protect gardenias from scales.
1. Recognizing Scale Infestation
Gardenias with the beginnings of a scale infestation may show no outward sign. In these cases, identifying scales by close physical examination may be the only method of detection. Entrenched and extensive infestations cause leaves to wilt or drop prematurely. Soft scale infestation is identifiable by the presence of honeydew, a sticky substance that can contaminate the plant and attract infectious agents such as sooty mold.
2. Immediate Control
If adult scales are detected on the stems, leaves or green parts of gardenias, they are already sapping essential juices. Removing these scales by scraping them off with your fingernail prevents immediate damage to the plants. The removal and destruction of the scales ensure they do not reattach themselves or rot and attract mold. This method works for the visible scales currently feeding on your gardenias but does not kill off younger scales, which are not sedentary.
3. Natural Predators
Insects such as the ladybird beetle, also known as the ladybug, are voracious predators that can hunt down scales for you. Natural predators are hunger-motivated protectors of your gardenias, hunting out and controlling populations of scales and other insect pests. Predator insects are especially beneficial because they attack adult scales that are immune to many chemical controls, as well as younger scales in the crawler stage. Scales that emit honeydew can attract ant colonies that defend the scales as a food source. This reduces the effectiveness of ladybugs as a control method.
4. Home Remedies
Some basic home remedies can help control scale populations on gardenias. Coating the green parts of gardenias with rubbing alcohol or soapy water makes removing attached scales less difficult and damaging to stems and leaves. Additionally, spraying the gardenias and surrounding soil with a solution of 1-percent canola oil mixed with water can suffocate scales in their crawler stage before they attach themselves to the plant.
After scales reach their adult stage and attach themselves to gardenias, they do not respond to most chemical controls. Because of this, many chemical control methods focus on scales while they are still in the crawler stage. Chemicals including bifenthrin, permethrin or carbaryl are applied directly to the plant as spray oil and can control scale infestations throughout the season. Soil-based insecticides, such as dinotefuran and imidacloprid also provide season-long scale control and prevent infestation without coating the gardenias.
- Missouri Botanical Garden: Gardenia Jasminoides
- Clemson University: Home & Garden Information Center: Gardenia Insects & Related Pests
- University of Hawaii: Cooperative Extension Service: Common Gardenia
- University of California Agriculture & Natural Resources: Pests in Gardens and Landscapes: Gardenia (Cape jasmine)
- University of California Agriculture & Natural Resources: Pests in Gardens and Landscapes: Scales
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