Fine threads of white wax dangling from the undersides of your hibiscus leaves indicate the shrubs are under attack from giant whiteflies (Aeleyrodicus dugesii.) If the waxy substance covers the upper leaf surfaces, the infestation is serious. Hibiscus, especially red and yellow varieties, attract whiteflies and eradicating these insects can be challenging. Because many whitefly species are now resistant to the insecticides that once controlled them, removing the pests from your hibiscus may require a multipronged approach.
Examine the undersides of newly infested hibiscus foliage. Look for leaves with large numbers of small, white oblong eggs and flat, oval stationary nymphs. Cut off the affected leaves with stem clippers and put them in plastic bags for disposal.
Dislodge heavier whitefly infestations by syringing -- targeting the leaves with a strong blast of water from a spray hose -- once a week. As the populations diminish, reduce syringing to every two or three weeks.
Remove large adult populations with a hand-held vacuum when they are lethargic from cool weather. Kill the insects by placing the vacuum's filter bag inside a plastic bag, leaving it in the freezer overnight and discarding it in the morning.
Treat chronic whitefly infestations by saturating your hibiscus foliage with a spray of insecticide, such as neem oil, that suffocates the nymphs or interferes with their metabolic processes. Spray at a temperature below 80 degrees when drought is not stressing the plants. Direct the spray where it will cover the nymphs, usually on the plant's lower leaves.
Make sticky-coated yellow traps to snare the insects on the hibiscus using quarter-inch plywood cut into 3 by 10-inch rectangles. Spray paint the traps brilliant yellow and nail them to wooden stakes. Mix a sticky coating using one part petroleum jelly to one part liquid dish detergent and apply it to one side of each trap with a paint brush. Position the traps in the ground with their painted surfaces facing your infested hibiscus. Shake the shrubs to agitate the insects; as they swarm, many will land on the yellow traps instead of returning to the plants. Clean the traps with soap and water and reapply the petroleum mixture as needed.
Things You Will Need
- Stem clippers
- Plastic bags
- Hose with sprayer attachment
- Hand-held vacuum
- Plastic bag
- Insecticidal soap or insecticidal oil spray
- 1/4-inch plywood
- Wooden stakes
- Brilliant yellow spray paint
- Petroleum Jelly
- Liquid dish detergent
- Paint brush
- Whiteflies often spread from hibiscus to other plants. Regular inspection and syringing of your entire garden minimizes their presence.
- When used to control giant whiteflies, clipping off affected leaves is more effective control on yellow than on red hibiscus.
- Hibiscus plants may be sensitive to neem oil spray; follow manufacturer's precautions.
- County of San Diego Department of Agriculture, Weights and Measures: Whiteflies
- UC IPM Online Managing Pests in Gardens and Landscapes: Giant Whitefly Management
- University of California Riverside Center for Invasive Species Research: Giant Whitefly
- UC IPM Online Managing Pests in Gardens and Landscapes: Hibiscus
- UC IPM Online Managing Pests in Gardens and Landscapes: Whiteflies
- Colorado State University Extension: Insect Control: Horticultural Oils
- Medioimages/Photodisc/Photodisc/Getty Images