Ask Mr. Smarty Plants

There are a number of hibiscus native to North America and to Florida, including Hibiscus aculeatus (comfortroot), Hibiscus grandiflorus (swamp rosemallow), Hibiscus laevis (halberdleaf rosemallow) and Hibiscus moscheutos (crimsoneyed rosemallow). There are many more hibiscus that are tropical in nature, and not native to North America. At the Lady Bird Johnson Wildflower Center, we are dedicated to the care and propagation of plants native to North America and to the area in which they are being grown.

Since we have no idea which or what hibiscus you have, we can only give you some very general information on what we think may be causing your problem.

Aphids and ants (from the University of California Integrated Pest Management site) are frequent pests of hibiscus.  Ants farm the aphids for "honey", a  secretion from the aphids. This secretion, on the underside of leaves, may eventually develop a sooty mold and give a dark color to the underside of the leaves.

Spider mites (from Ohio State University Extension) are so tiny they are difficult to see with the naked eye, but if you tap a leaf over a white sheet of paper, you will see little red dots if the spider mites are present. 

Mealy bugs (from Minnesota Dept. of Horticulture) are small flattened oval insects covered with a white powdery wax.

Whiteflies (from University of Missouri Extension) are sometimes referred to as "plant dandruff" and might be the reason for the white effect on your plant's branches. Like most of the others above, they suck on the plants juices, and can produce shriveling and browning. 

The good news is that most, if not all, of these pests can be controlled by directing a hard spray of water onto the plant, especially on the undersides of the leaves. Once washed off, the insects have difficulty getting back up. You can also use a weak solution of Safer insecticidal soap. 

Pictures of Hibiscus grandiflorus (swamp rosemallow)

Hibiscus aculeatus

Hibiscus laevis

Hibiscus moscheutos