Q. I have a tropical hibiscus plant that has developed white sticky spots on the leaves and stem. We had the plant outside during the summer, and then brought it indoors last fall. What’s going on?
A. Sounds as if you have mealy bugs on your hibiscus. Mealy bugs are pests of ornamental crops indoors and outdoors across the world. They are most active in warm, dry weather, so your indoor environment is perfect for them to develop. Mealy bugs damage plants by inserting their threadlike mouthparts into any part of the plant and sucking out sap. Like aphids or scale insects of trees, mealy bugs excrete honeydew, a sweet, sticky liquid. Sooty molds often grow in the honeydew causing infested plants to turn black.
Female mealy bugs have no wings and must be transported directly to or near the next host plant. They can travel short distances by crawling or may be blown about by the wind or carried on the feet of birds. This is how your plants became infested outdoors. Often there is a lag period between the first infestation and when eggs hatch and the pest becomes noticeable.
Each female mealy bug usually lays from 200 to 600 eggs. Some species of mealy bugs give birth to live young. Male nymphs secrete a tiny, fluffy cocoon and develop into winged adults. Males then fly about seeking females to mate with. Female mealy bugs are soft oval insects without wings. Very young nymphs are flat, oval and yellow. Older nymphs of some species are covered with fluffy, white wax.
Mealy bugs are usually found at the base of stems or petioles. After the first batch of eggs hatch, the infestation becomes very noticeable. As their numbers increase, mealy bugs of all sizes can be found crawling around or feeding on all surfaces of the plant.
Mealy bugs are not easy to control. This is because the eggs are enmeshed in waxy fluff and thus relatively waterproof. Likewise, adults and nymphs can be covered in wax to varying extents and obscured in plant nooks and crannies where it is difficult to get thorough pesticide coverage.
For this reason systemic insecticides might offer the most reliable control because they make the plant toxic to feed on rather than relying on contacting the insect directly. Bonide sells an indoor systemic insect control – available at some garden centers and on the Internet. It is important to use a product that states For Use Indoors on the label. I would still isolate the plant and treat it in a well-ventilated indoor area. One can also take the plant outdoors briefly to treat if the outside temperatures are above 45 degrees.
If an infestation is discovered early enough, the mealy bugs may be removed by a cotton swab dipped in alcohol or fingernail polish remover. Keep an eye on the plants for a few weeks to make sure no mealy bugs are overlooked.